Introduction

Light-emitting diodes (LEDs) are changing the lighting and display industry and have obtained significant advances compared to traditional lighting sources. Traditional material LEDs, e.g., III–V semiconductor LEDs1,2, organic LEDs (OLEDs)3,4, and quantum-dot LEDs (QLEDs)5, have achieved great success and gradually realized commercialization but still face some challenges. OLEDs have low carrier transport capability and exciton recombination, which hinders the improvement of the brightness. In addition, QLEDs show challenges in terms of the tedious manufacturing process, and the reliance on hydrophobic insulating long ligands also hinders their stability and electrical conductivity. Compared with these traditional materials, metal halide perovskites (MHPs) exhibit superior optoelectronic features that are beneficial for LED applications, such as high photoluminescence quantum yields (PLQYs), narrow full width at half maximum (FWHM), and feasible spectral tunability6,7,8,9,10. Perovskite LEDs (PeLEDs) have achieved impressive progress in the past few years since the first room-temperature PeLED was reported in 201411. Three types of perovskite materials with different dimensions (i.e., 3D perovskites, quasi-2D perovskites, and perovskite nanocrystals) are commonly included in the emitter layer of PeLEDs12,13,14,15,16. 3D PeLEDs have achieved EQEs of more than 20% in both the near-infrared and green regimes17,18. Simultaneously, PeLEDs based on perovskite nanocrystals have also shown prosperous development since they were first reported by Song et al. in 201519,20,21, achieving a record EQE of 23.4%22. Accordingly, the rapid progress achieved in high-performance PeLEDs indicates their promising applications, particularly in ultrahigh-definition displays, solid-state lighting, and photo-communication areas23,24.

Quasi-2D perovskites represent an important category of perovskites that possess self-assembled multi-quantum-well structures and have gained great success in light emission applications owing to their outstanding optoelectrical properties25,26. Calabrese et al.27 demonstrated that MAPbI3 (n = ∞) perovskite and (RNH3)2PbI4 (n = 1) perovskite represent two typical materials in the series of (RNH3)2MAn−1PbnI3n+1 (n = 1 to ∞). Thereafter, they reported the first quasi-2D perovskite, PEA2MAPb2I7, and the obtained crystallography data unambiguously confirmed the “bilayer” structure. Another pioneering work carried out by Mitzi et al.28 highlighted the structural “layered” characteristic of Sn-based perovskites (C4H9NH3)2(CH3NH3)n−1SnnI3n+1 (n = 1–5) through crystallographic characterization. Recently, substantial efforts have been made to obtain high-performance quasi-2D PeLEDs, which have facilitated unprecedented rapid development. In the past five years, we have witnessed the rapid development of quasi-2D perovskite optoelectronics, especially their tremendous success in LED applications. The recorded EQE of LEDs has soared to 21% and approached the efficiency limit22,29 since the first example was reported in 201630.

In particular, quasi-2D perovskites exhibit unique optical properties arising from their structural characteristics, which are different from those of conventional 3D11,31,32,33 and two-dimensional (2D) perovskites34,35. First, quasi-2D perovskites possess natural quantum-well structures, which can induce both dielectric- and quantum-confinement effects36,37,38,39,40. Such strong confinements thus afford a large exciton binding energy (Eb). In addition, quasi-2D films feature a mixed-phase rather than a single phase because the formation energies for different quasi-2D phases are quite similar41. During photoexcitation, the photocarriers transfer from higher bandgap species to lower bandgap species rapidly and efficiently, leading to accumulated carriers in the recombination centers. The increased carrier density then effectively passivates the defect states, thereby significantly improving the radiative recombination efficiency and the resulting PLQYs30,42. In addition, quasi-2D perovskites exhibit tunability of their spectra, which can be modulated through composition and dimensionality engineering respectively. These characteristics enable continuous photoluminescence (PL) wavelength tuning from violet to near-infrared (NIR) spectral regions29,43,44,45.

However, the performance and stability of quasi-2D PeLEDs still cannot meet the requirements for commercialization at the moment. More efforts need to be devoted to exploring the optical and electrical properties of these materials. In addition, investigation of the correlation between the device performance and the underlying photophysics of the materials appears to be particularly important. Following this trend, we discuss the inherent optical properties and corresponding photophysics of quasi-2D perovskites at the beginning of the review. We then summarize the progress in spectral tunability of quasi-2D perovskites, mainly to realize high-performance pure-red and pure-blue emission. Next, we discuss the newly emerged device engineering approaches to produce high-performance quasi-2D PeLEDs. Finally, we summarize the key challenges in the field and propose several promising research opportunities to facilitate the development of highly stable and high-performance quasi-2D materials and devices. The review article thus paves the way for future quasi-2D PeLED manufacture.

Characteristics of quasi-2D perovskites

Structural characteristics

Employing bulky organic cations to substantially replace the traditional small cations breaks the original continuous 3D structure and generates a stable quasi-2D geometry. The geometry can be understood as slicing the 3D structure in planes along the <100> crystallographic directions46,47,48. As shown in Fig. 1a, large organic amines are introduced during crystal growth, which cannot enter the gap between [BX6]4− octahedrons, thus inhibiting the growth of [BX6]4− along out-of-plane directions49,50. The sheets of quasi-2D perovskite unit cells are periodic along the basal plane and are constrained in the perpendicular direction. Generally, quasi-2D perovskites possess the chemical formula A′2An−1BnX3n+1 (1 ≤ n ≤ ∞), where A′ refers to a large organic cation, including monoammonium cations (R-NH3+) and diammonium cations (+H3N-R-NH3+) (R represents an alkyl chain or aromatic ligand); A stands for a small monovalent cation, e.g., methylammonium (MA+ = CH3NH3+), formamidine (FA+ = CH(NH2)2+), or cesium (Cs+); B is a divalent metal cation such as lead (Pb2+) or tin (Sn2+); X represents a halide, e.g., chloride (Cl−), bromide (Br−) or iodide (I−); and n refers to the number of [BX6]4− octahedral units. In brief, A′ acts as an insulating layer to isolate the inorganic layers (the metal halide [BX6]4− octahedral units) linked together by corner-sharing halide anions, and A cations occupy voids within the framework30,42.

Fig. 1: Structure and photophysical properties of a quasi-2D perovskite.
figure 1

a (i) Schematic representation of a quasi-2D perovskite, which can be obtained by slicing the 3D perovskite along the <100> crystallographic direction. (ii) Schematic crystal structures of quasi-2D perovskites with different n-values. (iii) Electronic properties of quasi-2D perovskites, which are determined by the degree of quantum- and dielectric-confinement effects. b Eb and PL emission wavelength of quasi-2D perovskites as a function of n-value. Panel b is reprinted from ref. 51 with permission from Wiley

Full size image

Quasi-2D perovskites consist of a series of alternately aligned inorganic and organic layers. Inorganic [BX6]4− octahedral sheets are sandwiched by two layers of large organic spacers with relatively low dielectric constants. Specifically, the inorganic [BX6]4− slabs act as quantum “wells”, while the organic cap** layers function as “barriers”. Thus, the “quantum-well” (QW) structures of a quasi-2D perovskite are formed naturally with an atomically sharp interface between “barriers” and “wells” (Fig. 1a). Due to the quantum- and dielectric-confinement effects arising from the QW structure, the Eb of a quasi-2D perovskite becomes larger than that of its 3D analog25,42. The carrier wave function is compressed in one direction due to the QW width limitation. Accordingly, the carrier movement is limited, which increases the resulting Eb and effective bandgap of quasi-2D perovskites. In particular, both electrons and holes are confined within the inorganic well; stronger binding energy facilitates the formation of stable excitons at room temperature, thereby increasing the radiative recombination efficiency. Furthermore, the confinement intensity is dependent on the thickness of the QWs, which provides additional flexibility to tune the corresponding bandgap and carrier recombination dynamics51 (Fig. 1b). The selection of barriers with different dielectric constants affects the Eb value, referred to as the “dielectric confinement” effect. Ishihara et al.52 noted that the large Eb (370 meV) was too large to be explained only by the quantum confinement effect. Therefore, the dielectric confinement effect was raised53. Kanatzidis et al. simulated a high-frequency dielectric constant (ε∞) profile for different n-values of the BA2MAn−1PbnI3n+1 (BA+ = CH3(CH2)3NH3+, MA+ = CH3NH3+) family54. They demonstrated an increasing ε∞ for inorganic slabs with increasing n-value. The dielectric confinement dominates at n = 1, weakens at n = 5, and completely disappears in the 3D perovskite (n = ∞). Therefore, the dielectric confinement in quasi-2D perovskites also accounts for the corresponding high Eb, and the dielectric confinement decreases as the n-value increases (Fig. 1b).

The robustness of the excitonic states at room temperature is the most prominent optical feature of quasi-2D perovskites, which originates from their large Eb. Fortunately, Eb can be regulated through composition and structure engineering. Basically, incorporating organic cations with different dielectric constants into the quasi-2D structure can significantly tune the dielectric confinement effect55,56. In addition, Eb can also be modulated due to confinement effects by varying the thickness of the QWs40. The large Eb and thus prominent excitonic luminescence are unique features of quasi-2D perovskites with application in LEDs.

Photophysical properties

Ishihara et al. successively grew quasi-2D single crystals with n = 1, 2, 3, and 427,28,52. Afterward, Kanatzidis et al. synthesized and structurally characterized the n = 5 (CH3(CH2)3NH3)2(CH3NH3)4Pb5I16 perovskite54. To date, the maximum n-value quasi-2D perovskite reported is the n = 7 (CH3(CH2)2NH3)2(CH3NH3)6Pb7I22 perovskite57. Significantly, the high-quality quasi-2D single-crystal confirms that the structure is thermodynamically stable, which lays the foundation for further optoelectronic applications. The carrier recombination dynamics of quasi-2D perovskite single crystals with various n-values were systematically studied to deeply understand the photophysical properties of quasi-2D perovskites.

The carrier recombination dynamics of quasi-2D perovskites can typically be described by the following Eq. (1)58,59:

$$\frac{{{\mathrm{d}}N(t)}}{{{\mathrm{d}}t}} = - k_1N - k_2N^2 - k_3N^3$$
(1)

Here, N represents the carrier density at delay time t; k1 refers to the monomolecular recombination constant; k2 is the bimolecular recombination constant, and k3 is the three-body Auger (nonradiative) recombination constant. Chen et al.60 studied the charge-carrier recombination in quasi-2D perovskite single crystals using transient reflection (TR) spectroscopy. TR kinetics at different excitation fluences were then globally fitted to obtain k1, k2, and k3 for different n-value PEA2MAn−1PbnI3n+1 crystals. They found that the existence of excitons and free carriers varied in quasi-2D perovskite single crystals with different n-values. The largest k1 was found in the n = 1 sample, which can be attributed to its large Eb, indicating that excitons were dominant in this species, while for the n = 4 sample, free carriers dominated; for the n = 2 and 3 samples, free carriers and excitons coexisted. Additionally, Delport et al.61 investigated the recombination dynamics in (C6H5C2H4NH3)2(CH3NH3)n−1PbnI3n+1 (n = 1, 2, 3, and 4) single crystals. They first studied the scaling law of PL0 (the PL intensity at t = 0 ns, at the instant of pulse excitation) with excitation fluence, which is a classical method used to analyze the recombination behavior. For the n = 1 2D single crystal, PL0 was linear with the excitation density, showing the predominant exciton recombination characteristic. However, for n > 1 single crystals, the nonlinear relationship between PL0 and the pump density proved the coexistence of free carrier and exciton recombination. The associated optical and electrical properties seemed to further diverge from those of the pure excitonic compound as the n-value increased. To conclude, in low n-value quasi-2D perovskites, Eb is large, which guarantees efficient exciton recombination. In high n-value species, the excitons tend to dissociate into free carriers as Eb decreases (Fig. 2b). The above carrier recombination dynamics in quasi-2D perovskite single crystals have established the potential use of quasi-2D perovskites as optoelectronic materials, such as in solar cells and LEDs.

Fig. 2: Charge-carrier recombination kinetics in quasi-2D perovskite films.
figure 2

a TA spectra at different timescales, b TA spectra at different wavelengths as a function of delay time, c PL spectra at distinct timescales, and d PL decay curve probed at selected wavelengths for <n> = 3 perovskites. Comparison of e initial time PL intensities and f PLQYs as a function of the photoinjected carrier density between 3D and quasi-2D perovskite films. Panels a–d are reprinted from ref. 30 with permission from Springer Nature. Panels e and f are reprinted from ref. 30 carried out ultrafast spectroscopy to investigate the carrier recombination kinetics for (PEA)2MAn−1PbnI3n+1 quasi-2D perovskite films. Intriguingly, the TA spectra exhibited four distinctive bleaching peaks in <n> = 3 (<n> represents the average “QW” thickness) films ascribed to n = 2, 3, 4, and 5 species. Figure 2a shows the relative intensity evolution of these bleaching peaks. The data demonstrated that carriers transfer from small n-value species to large n-value species. The build-up time for GSB of lower bandgap species was in good agreement with the fast decay time of higher bandgap species, which was less than 1 ps and indicated that the energy transfer was ultrafast (Fig. 2b). Time-resolved photoluminescence (TRPL) measurements revealed the same trend (Fig. 2c). Specifically, the lower bandgap species exhibited a biexponential decay, and the corresponding fast component was attributed to carrier funneling from large bandgap species (Fig. 2d).

**ng et al.62 investigated the power-dependent initial PL intensity (IPL [t = 0]) for (NMA)2FAn−1PbnI3n+1 quasi-2D perovskite films (Fig. 2e). Notably, IPL [t = 0] was linear with excitation density below 1.5 × 1016 cm−3, while a clear transition from linear to superlinear was observed when the excitation density increased continuously. They demonstrated that monomolecular radiative exciton recombination was dominant under a low carrier density and gradually changed to free electron-hole bimolecular recombination as the carrier density increased further. Consequently, the PLQY of a quasi-2D perovskite can be given by the following equation62:

$${\mathrm{PLQY}}\left( N \right) = \frac{{{\sum} {k_{\mathrm{r}}} }}{{{\sum} {k_{\mathrm{r}} + {\sum} {k_{{\mathrm{nr}}}} } }} = \frac{{k_{1,{\mathrm{exciton}}} + k_2N}}{{k_{1,{\mathrm{exciton}}} + k_{1,{\mathrm{trap}}} + k_2N + k_3N^2}}$$
(2)

Here, the monomolecular recombination constant k1 contains both k1,exciton and k1,trap, where k1,exciton is the radiative exciton recombination constant and k1,trap is the nonradiative trap-assisted recombination constant. The PLQY only depends on two physical processes, namely, radiative recombination (kr) and nonradiative recombination (knr), and is the result of competition between these two channels. Specifically, for quasi-2D perovskites, radiative recombination includes exciton recombination (k1,exciton) and free carrier recombination (k2); nonradiative recombination includes trap-assisted recombination (k1,trap) and Auger recombination (k3). In addition, these recombination rate constants (k1, k2, and k3) strongly depend on the carrier concentration (N). Therefore, the PLQY of quasi-2D perovskite films is dependent on N. At low N, PLQY only depends on the competition between k1,exciton and k1,trap. Fortunately, the high PLQY and near invariant dependence for quasi-2D perovskite films at carrier densities below 1016 cm3 validated that radiative exciton recombination overwhelmed trap-mediated nonradiative recombination70. For quasi-2D perovskite films, the n-value distribution affects their energy transfer and corresponding radiative exciton recombination efficiency. Fortunately, the n-value distribution can be modulated through fabrication process engineering71,108. Previous reports demonstrated that introducing Rb+ (RRb+ = 1.52 Å) into a perovskite resulted in a significant increase in the bandgap due to the tilt of the inorganic octahedron and the reduction in orbital overlap109. The bandgap of RbxCs1−xPbBr3 perovskite films increased from 2.31 to 2.60 eV (0 ≤ x ≤ 0.8) with increasing Rb+. Jiang et al.110 partially substituted Cs+ with Rb+ and fabricated alloy PEA2(RbxCs1−x)2Pb3Br10 films. The small-radius Rb+ increased the optical bandgap of these films and realized blue emission within the range of ~450–490 nm (Fig. 6d). Moreover, alloy PEA2(RbxCs1−x)2Pb3Br10 films exhibited impressive spectral stability compared with the mixed-halide films since the undesired halide migration or Ostwald ripening had been overcome. Recently, Chu et al. used EA+ (CH3CH2NH3+) to partially replace Cs+ and achieved pure-blue emission in PEA2(EAxCs1−xPbBr3)2PbBr4 perovskite. They claimed that the incorporation of EA+ could decrease the Pb-Br orbital coupling and increase the bandgap (Fig. 6e). This strategy modulated the PL peak from the green region (508 nm) to the blue region (466 nm) with increasing EA+ (Fig. 6f), and over 70% PLQY in blue emission was obtained45. Lanzetta et al.111 reported the 2D perovskite materials (PEA)2SnIxBr4−x with tunable optical properties in the visible spectral region. Limited to the manufacturing technology at that time, they only fabricated PeLEDs with extremely poor performance at 630 nm. Subsequently, Yuan et al.112 developed a strategy to improve the film quality and protect Sn2+ from oxidation by adding valeric acid (VA). They fabricated color-pure red PEA2SnI4 LEDs with an EQE of 5% and a lifetime of >15 h.

In conclusion, cation engineering of the “A-site” or “B-site” is another feasible strategy to achieve pure red and blue emission. This strategy dramatically slows down the spectral redshift caused by halogen segregation, thus showing excellent application potential in long-term stable quasi-2D PeLEDs. The “A-site” and “B-site” options are still limited, and researchers should exploit more suitable inorganic or organic cations to provide further breakthroughs.

Dimensionality engineering

Quasi-2D perovskites with high structural tunability can enable flexible regulation of the quantum-confinement effect. Reducing the average <n> value of the film enhances the quantum-confinement effect, broadens the perovskite bandgap, and results in spectral blueshift. Thus, dimensionality engineering offers an efficient approach for spectral manipulation86,97. The average <n> values of quasi-2D perovskite films are determined by the equilibrium between the large organic cations and the precursor88. In theory, increasing the content of large organic cations can monotonically reduce the <n> value of quasi-2D perovskite films. However, this does not mean that quasi-2D perovskite films with low <n> values are sufficient to effectively realize pure red or blue emission. For instance, increasing the content of large organic cations results in excessive generation of a low n-value phase, which leads to inefficient energy transfer and reduced optical properties113. Meanwhile, poor charge transport properties arise from large amounts of insulating organic cations. Moreover, the strong electron–phonon coupling and exciton–exciton annihilation at small <n> values act as nonradiative recombination pathways and further deteriorate the optical properties114.

Judicious phase modulations towards a narrow phase distribution are highly desired to realize pure red and blue emission, which would address the severe optical property degradation in small <n> value films44,115,116,117,118,119,120. Controlling crystallization by antisolvent techniques or rational large cation spacers and additives can narrow the phase distribution72,115. **ng et al. selected the short organic cation isopropylammonium (IPA+) to partially replace the longer cation (PEA+) in PEA2A1.5Pb2.5Br8.5 (A = MA+ and Cs+) films, which can modulate the crystallization and phase distribution in the quasi-2D perovskite. Theoretical calculations showed that the formation energy of the n = 1 phase changed from −7.2 (more stable) to −6.5 eV (less stable) when these two cations were used synergistically (Fig. 7a). Thus, increasing the IPA+/Pb2+ ratio suppressed the formation of the n = 1 phase and inhibited high-n phase generation afterward, while the intermediate n phases (n = 2, 3, 4) grew faster instead (Fig. 7b). Simultaneously, the PL peaks blueshifted from 497 to 467 nm as the IPA+/Pb2+ ratio increased from 10 to 60%121. As a result, the resultant films displayed high PLQYs and stable blue emission by modulating the phase judiciously, thereby fabricating efficient and spectrally stable sky-blue quasi-2D PeLEDs. Since then, the effect of mixed organic cations on the properties of quasi-2D perovskites has been extensively studied.

Fig. 7: Phase modulation of quasi-2D perovskites for effective blue emission.
figure 7

a Calculated formation energy of PEABr- and IPABr-based perovskites and their mixed quasi-2D perovskites with different n-values. Inset: Atomic model of the PEA/IPA mixed quasi-2D perovskite with n = 3. b UV-vis absorption spectra of the perovskite PEA2A1.5Pb2.5Br8.5 with different amounts of IPABr additive. c Schematic diagram of the chelating effect on PbBr2 binding to the surface. d DFT-calculated destabilization energy of PbBr2 on the quasi-2D perovskite surface when coordinated with GABA and PEA. TA spectra at different timescales for e (PEA)2Cs2Pb3Br10 and f GABA-treated (PEA)2Cs2Pb3Br10 perovskite films. Panels a and b are reprinted from ref. 121 with permission from Springer Nature. Panels c–f are reprinted from ref. 122 with permission from Springer Nature

Full size image

In addition to mixed-cation strategies, a judicious phase distribution can be achieved by rationally screening additives. Wang et al.122 incorporated a chelating agent, γ-aminobutyric acid (GABA), into a PEA2Csn−1PbnBr3n+1 film. Theoretical calculations indicated that the coordination tendency of small chelating molecules towards PbBr2 in the vicinity of the perovskite could inhibit the binding of PbBr2 to the perovskite surface, suppressing the growth of the large n phase. Replacing the unidentate group (PEA+) with a small bidentate molecule (GABA) resulted in a 10-fold increase in the destabilization energy (0.51 eV), which increased further when two GABA molecules were utilized for coordination (Fig. 7c, d). The photoexcited carrier dynamics of the GABA-treated quasi-2D perovskite films adequately proved that the resulting phase distribution was concentrated at n = 2 and 3 (Fig. 7e, f). The efficient energy transfer from the judicious phase distribution of the films can increase the PLQY and realize true-blue emission (EL at 478 nm)122. In conclusion, after a series of artificial designs and interventions regarding the phase distribution, the optical properties of pure red and blue quasi-2D perovskite films have significantly improved, paving the way for high-performance pure red and blue quasi-2D PeLED manufacture. In our opinion, successful fabrication of high-performance quasi-2D PeLEDs with pure red and blue emission that satisfy display purposes might require a combination of strategies leveraging anion engineering, cation engineering of the “A-site” or “B-site,” and dimensionality engineering.

High-performance quasi-2D PeLEDs

Highly emissive perovskite layers are not sufficient to obtain high-performance quasi-2D PeLEDs due to the difference between photoluminescence and electroluminescence. The working principle and important parameters of PeLEDs need to be specifically considered. PeLEDs can be simplified into a double-heterojunction structure, in which the perovskite emitter layer is sandwiched between the p-type hole transport layer (HTL) and the n-type electron transport layer (ETL)123. Under a forward voltage, holes and electrons are injected from the anode and cathode, respectively, and are confined in the perovskite layer. Then, the holes and electrons release photons through radiative recombination. The key parameters, including the EL peak, FWHM, luminance, turn-on voltage (Von), EQE, and operational stability, are used to evaluate the performance of PeLEDs124 (Table 1). For display devices with a wide color gamut, LEDs usually need to have a specific EL peak and a narrow FWHM to achieve emission purity, while in the case of white-light devices for solid-state lighting, the devices have a wide emission range and FWHM. The luminances of LEDs are usually between 200 and 1000 cd m−2 for display applications and exceed 10,000 cd m−2 for solid-state lighting125. Von refers to the voltage when the luminance of the device reaches 1 cd m−2. A low Von represents an effective injection of carriers. The operational stability of PeLEDs is usually evaluated by T50, which represents the time for the luminance to drop to half of its initial value when working at a fixed current or voltage.

EQE is defined as the ratio of the number of photons emitted by the device to the number of electrons injected and is the most important indicator for judging the energy conversion efficiency of LEDs. EQE can be expressed as the product of the internal quantum efficiency (IQE) and light extraction efficiency (ηoc)126.

$${\mathrm{EQE}} = {\mathrm{IQE}} \times \eta _{{\mathrm{oc}}} = \gamma \times \chi \times \eta _{{\mathrm{PL}}} \times \eta _{{\mathrm{oc}}}$$
(3)

Here, IQE is defined as the ratio of the number of photons generated to the number of electrons injected into the LED; ηoc represents the ratio of the number of photons emitted to the outside to the number of photons generated in the active layer; γ represents the charge injection balance factor; χ refers to the fraction of excitons for radiative decay, and ηPL is the PLQY127. ηPL has been detailed before, and ηoc will be elaborated below. Here, we focus on γ and χ, which relate to the device structure and electrical factors. Device engineering, such as optimization of the charge transport layers of quasi-2D PeLEDs, could promote the charge injection balance factor towards its maximum (γ = 1)128. In addition, the use of electron- and hole-blocking layers can confine the charge carriers in the emitting layer and thus lead to enhanced charge balance. The use of interfacial engineering to reduce the exciton quenching at each interface of the device could promote the fraction of excitons for radiative decay (χ)129. Based on Eq. (3), we summarize three aspects to improve the electrical properties in quasi-2D PeLEDs, including function layer modulation, interfacial engineering, and light out-coupling technologies. Finally, the operational stability is another critical parameter of quasi-2D PeLEDs, and we then overview several possible reasons for degradation130.

Functional layer optimization

To convert high PLQYs of quasi-2D perovskite films into high EQEs of quasi-2D PeLEDs, the band alignment of the device structure is the most basic consideration. Typically, PeLEDs have a sandwich device structure in which the perovskite emissive layer is located between the electron and hole transport layers. Ideally, the charge balance factor can be maximized to 1 (γ = 1) by optimizing the charge transport layer. The energy levels for different transport layer materials (TLMs), including HTLs and ETLs, are shown in Fig. 8a. Appropriate TLMs should have ideal energy levels for efficient carrier transport while blocking opposite carrier transport. In addition, the carrier mobility of different TLMs also affects the carrier injection balance. For ETLs, PO-T2T (2,4,6-tris[3-(diphenylphosphinyl) phenyl]-1,3,5-triazine) can enable overall performance improvements compared to B3PYMPM (4,6-bis(3,5-di(pyridin-3-yl) phenyl)-2-methylpyrimidine) and TPBi (2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidalzole))131. The deeper HOMO level (−7.5 eV) and the superior electron mobility (∼10−3 cm2 V−1 s−1) account for the excellent electron transport and hole-blocking properties of PO-T2T. For HTLs, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is commonly used, and its work function is ∼5.2 eV132. Notably, in terms of hole injection, a large barrier exists between PEDOT:PSS and the perovskite layer with a deeper valence band, especially in green and blue emitters. Fortunately, this predicament can be overcome by employing poly(sodium 4-styrenesulfonate) (PSS-Na) to increase the work function of PEDOT:PSS45,81,133. PEDOT:PSS doped with perfluorinated ionomer (PFI) can also achieve similar effects79,104. In addition, HTLs with low HOMO levels, such as poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB), poly(9-vinlycarbazole) (PVK), and poly[bis(4-phenyl)(4-butylphenyl)amine] (poly-TPD), were deposited on PEDOT:PSS to form gradient energy levels for hole injection, which can also achieve charge balance effectively

References

  1. Okumura, H., Misawa, S. & Yoshida, S. Epitaxial growth of cubic and hexagonal GaN on GaAs by gas-source molecular-beam epitaxy. Appl. Phys. Lett. 59, 1058–1060 (1991).

    Article  ADS  Google Scholar 

  2. Duffy, M. T. et al. Epitaxial growth and piezoelectric properties of A1N, GaN, and GaAs on sapphire or spinel. J. Electron. Mater. 2, 359–372 (1973).

    Article  ADS  Google Scholar 

  3. Wu, T. L. et al. Diboron compound-based organic light-emitting diodes with high efficiency and reduced efficiency roll-off. Nat. Photonics 12, 235–240 (2018).

    Article  ADS  Google Scholar 

  4. Baldo, M. A. et al. Highly efficient phosphorescent emission from organic electroluminescent devices. Nature 395, 151–154 (1998).

    Article  ADS  Google Scholar 

  5. Dai, X. L. et al. Solution-processed, high-performance light-emitting diodes based on quantum dots. Nature 515, 96–99 (2014).

    Article  ADS  Google Scholar 

  6. Quan, L. N. et al. Perovskites for next-generation optical sources. Chem. Rev. 119, 7444–7477 (2019).

    Article  Google Scholar 

  7. He, T. W. et al. Structured perovskite light absorbers for efficient and stable photovoltaics. Adv. Mater. 32, 1903937 (2020).

    Article  Google Scholar 

  8. He, T. W. et al. Reduced-dimensional perovskite photovoltaics with homogeneous energy landscape. Nat. Commun. 11, 1672 (2020).

    Article  ADS  Google Scholar 

  9. Wang, L. et al. A chiral reduced-dimension perovskite for an efficient flexible circularly polarized light photodetector. Angew. Chem. Int. Ed. 59, 6442–6450 (2020).

    Article  Google Scholar 

  10. Huang, Y. M. et al. A-site cation engineering for highly efficient MAPbI3 single-crystal X-ray detector. Angew. Chem. Int. Ed. 58, 17834–17842 (2019).

    Article  Google Scholar 

  11. Tan, Z. K. et al. Bright light-emitting diodes based on organometal halide perovskite. Nat. Nanotechnol. 9, 687–692 (2014).

    Article  ADS  Google Scholar 

  12. Xu, W. D. et al. Rational molecular passivation for high-performance perovskite light-emitting diodes. Nat. Photonics 13, 418–424 (2019).

    Article  ADS  Google Scholar 

  13. Zhao, X. F. et al. Opportunities and challenges in perovskite light-emitting devices. ACS Photonics 5, 3866–3875 (2018).

    Article  Google Scholar 

  14. Li, G. R. et al. Efficient light-emitting diodes based on nanocrystalline perovskite in a dielectric polymer matrix. Nano Lett. 15, 2640–2644 (2015).

    Article  ADS  Google Scholar 

  15. Chiba, T. et al. Anion-exchange red perovskite quantum dots with ammonium iodine salts for highly efficient light-emitting devices. Nat. Photonics 12, 681–687 (2018).

    Article  ADS  Google Scholar 

  16. Zhao, B. D. et al. High-efficiency perovskite-polymer bulk heterostructure light-emitting diodes. Nat. Photonics 12, 783–789 (2018).

    Article  ADS  Google Scholar 

  17. Cao, Y. et al. Perovskite light-emitting diodes based on spontaneously formed submicrometre-scale structures. Nature 562, 249–253 (2018).

    Article  ADS  Google Scholar 

  18. Lin, K. B. et al. Perovskite light-emitting diodes with external quantum efficiency exceeding 20 per cent. Nature 562, 245–248 (2018).

    Article  ADS  Google Scholar 

  19. Yong, Z. J. et al. Do**-Enhanced short-range order of perovskite nanocrystals for near-unity violet luminescence quantum yield. J. Am. Chem. Soc. 140, 9942–9951 (2018).

    Article  Google Scholar 

  20. Koscher, B. A. et al. Essentially trap-free CsPbBr3 colloidal nanocrystals by postsynthetic thiocyanate surface treatment. J. Am. Chem. Soc. 139, 6566–6569 (2017).

    Article  Google Scholar 

  21. Shan, Q. S. et al. High performance metal halide perovskite light-emitting diode: from material design to device optimization. Small 13, 1701770 (2017).

    Article  Google Scholar 

  22. Kim, Y. H. et al. Comprehensive defect suppression in perovskite nanocrystals for high-efficiency light-emitting diodes. Nat. Photonics https://doi.org/10.1038/s41566-020-00732-4 (2021).

  23. Bao, C. X. et al. Bidirectional optical signal transmission between two identical devices using perovskite diodes. Nat. Electron. 3, 156–164 (2020).

    Article  Google Scholar 

  24. Luo, J. J. et al. Efficient and stable emission of warm-white light from lead-free halide double perovskites. Nature 563, 541–545 (2018).

    Article  ADS  Google Scholar 

  25. Cheng, L. et al. Multiple-quantum-well perovskites for high-performance light-emitting diodes. Adv. Mater. 32, 1904163 (2020).

    Article  Google Scholar 

  26. Jiang, Y. Z. et al. Reduced-dimensional α-CsPbX3 perovskites for efficient and stable photovoltaics. Joule 2, 1356–1368 (2018).

    Article  Google Scholar 

  27. Calabrese, J. et al. Preparation and characterization of layered lead halide compounds. J. Am. Chem. Soc. 113, 2328–2330 (1991).

    Article  Google Scholar 

  28. Mitzi, D. B. et al. Conducting tin halides with a layered organic-based perovskite structure. Nature 369, 467–469 (1994).

    Article  ADS  Google Scholar 

  29. Miao, Y. F. et al. Microcavity top-emission perovskite light-emitting diodes. Light. Sci. Appl. 9, 89 (2020).

    Article  ADS  Google Scholar 

  30. Yuan, M. J. et al. Perovskite energy funnels for efficient light-emitting diodes. Nat. Nanotechnol. 11, 872–877 (2016).

    Article  ADS  Google Scholar 

  31. Kim, Y. H. et al. Multicolored organic/inorganic hybrid perovskite light-emitting diodes. Adv. Mater. 27, 1248–1254 (2015).

    Article  Google Scholar 

  32. Wang, J. P. et al. Interfacial control toward efficient and low-voltage perovskite light-emitting diodes. Adv. Mater. 27, 2311–2316 (2015).

    Article  Google Scholar 

  33. Zhang, F. J. et al. Efficient blue perovskite light-emitting diodes boosted by 2D/3D energy cascade channels. Adv. Funct. Mater. 30, 2001732 (2020).

    Article  Google Scholar 

  34. Hong, X., Ishihara, T. & Nurmikko, A. V. Photoconductivity and electroluminescence in lead iodide based natural quantum well structures. Solid State Commun. 84, 657–661 (1992).

    Article  ADS  Google Scholar 

  35. Era, M. et al. Organic-inorganic heterostructure electroluminescent device using a layered perovskite semiconductor (C6H5C2H4NH3)2PbI4. Appl. Phys. Lett. 65, 676–678 (1994).

    Article  ADS  Google Scholar 

  36. Kumagai, M. & Takagahara, T. Excitonic and nonlinear-optical properties of dielectric quantum-well structures. Phys. Rev. B 40, 12359 (1989).

    Article  ADS  Google Scholar 

  37. Tanaka, K. et al. Image charge effect on two-dimensional excitons in an inorganic-organic quantum-well crystal. Phys. Rev. B 71, 045312 (2005).

    Article  ADS  Google Scholar 

  38. Zhang, S. T. et al. Efficient red perovskite light-emitting diodes based on solution-processed multiple quantum wells. Adv. Mater. 29, 1606600 (2017).

    Article  Google Scholar 

  39. Traore, B. et al. Composite nature of layered hybrid perovskites: assessment on quantum and dielectric confinements and band alignment. ACS Nano 12, 3321–3332 (2018).

    Article  Google Scholar 

  40. Katan, C., Mercier, N. & Even, J. Quantum and dielectric confinement effects in lower-dimensional hybrid perovskite semiconductors. Chem. Rev. 119, 3140–3192 (2019).

    Article  Google Scholar 

  41. Quan, L. N. et al. Ligand-stabilized reduced-dimensionality perovskites. J. Am. Chem. Soc. 138, 2649–2655 (2016).

    Article  Google Scholar 

  42. Wang, N. N. et al. Perovskite light-emitting diodes based on solution-processed self-organized multiple quantum wells. Nat. Photonics 10, 699–704 (2016).

    Article  ADS  Google Scholar 

  43. Wu, C. et al. Alternative type two-dimensional-three-dimensional lead halide perovskite with inorganic sodium ions as a spacer for high-performance light-emitting diodes. ACS Nano 13, 1645–1654 (2019).

    Google Scholar 

  44. He, Z. F. et al. High-efficiency red light-emitting diodes based on multiple quantum wells of phenylbutylammonium-cesium lead iodide perovskites. ACS Photonics 6, 587–594 (2019).

    Article  Google Scholar 

  45. Chu, Z. M. et al. Large cation ethylammonium incorporated perovskite for efficient and spectra stable blue light-emitting diodes. Nat. Commun. 11, 4165 (2020).

    Article  ADS  Google Scholar 

  46. Mitzi, D. B. et al. Conducting layered organic-inorganic halides containing <110>-oriented perovskite sheets. Science 267, 1473–1476 (1995).

    Article  ADS  Google Scholar 

  47. Mitzi, D. B. In Progress in Inorganic Chemistry (ed. Karlin, K. D.) 1–121 (1999).

  48. Liang, H. Y. et al. High color purity lead-free perovskite light-emitting diodes via Sn stabilization. Adv. Sci. 7, 1903213 (2020).

    Article  Google Scholar 

  49. Sichert, J. A. et al. Quantum size effect in organometal halide perovskite nanoplatelets. Nano Lett. 15, 6521–6527 (2015).

    Article  ADS  Google Scholar 

  50. Ortiz-Cervantes, C., Carmona-Monroy, P. & Solis-Ibarra, D. Two-dimensional halide perovskites in solar cells: 2D or not 2D? ChemSusChem 12, 1560–1575 (2019).

    Article  Google Scholar 

  51. Quan, L. N. et al. Perovskites for light emission. Adv. Mater. 30, 1801996 (2018).

    Article  Google Scholar 

  52. Ishihara, T., Takahashi, J. & Goto, T. Exciton state in two-dimensional perovskite semiconductor (C10H21NH3)2PbI4. Solid State Commun. 69, 933–936 (1989).

    Article  ADS  Google Scholar 

  53. Ishihara, T., Takahashi, J. & Goto, T. Optical properties due to electronic transitions in two-dimensional semiconductors (CnH2n+1NH3)2PbI4. Phys. Rev. B 42, 11099 (1990).

    Article  ADS  Google Scholar 

  54. Stoumpos, C. C. et al. High members of the 2D Ruddlesden-Popper halide perovskites: synthesis, optical properties, and solar cells of (CH3(CH2)3NH3)2(CH3NH3)4Pb5I16. Chem 2, 427–440 (2017).

    Article  Google Scholar 

  55. Gan, L. et al. Effects of organic cation length on exciton recombination in two-dimensional layered lead iodide hybrid perovskite crystals. J. Phys. Chem. Lett. 8, 5177–5183 (2017).

    Article  Google Scholar 

  56. Ni, L. M. et al. Real-time observation of exciton-phonon coupling dynamics in self-assembled hybrid perovskite quantum wells. ACS Nano 11, 10834–10843 (2017).

    Article  Google Scholar 

  57. Soe, C. M. M. et al. Structural and thermodynamic limits of layer thickness in 2D halide perovskites. Proc. Natl Acad. Sci. USA 116, 58–66 (2019).

    Article  Google Scholar 

  58. Yaffe, O. et al. Excitons in ultrathin organic-inorganic perovskite crystals. Phys. Rev. B 92, 045414 (2015).

    Article  ADS  Google Scholar 

  59. Feldmann, S. et al. Photodo** through local charge carrier accumulation in alloyed hybrid perovskites for highly efficient luminescence. Nat. Photonics 14, 123–128 (2020).

    Article  ADS  Google Scholar 

  60. Chen, X. H. et al. Impact of layer thickness on the charge carrier and spin coherence lifetime in two-dimensional layered perovskite single crystals. ACS Energy Lett. 3, 2273–2279 (2018).

    Article  Google Scholar 

  61. Delport, G. et al. Exciton-exciton annihilation in two-dimensional halide perovskites at room temperature. J. Phys. Chem. Lett. 10, 5153–5159 (2019).

    Article  Google Scholar 

  62. **ng, G. C. et al. Transcending the slow bimolecular recombination in lead-halide perovskites for electroluminescence. Nat. Commun. 8, 14558 (2017).

    Article  ADS  Google Scholar 

  63. Byun, J. et al. Efficient visible quasi-2D perovskite light-emitting diodes. Adv. Mater. 28, 7515–7520 (2016).

    Article  Google Scholar 

  64. Quintero-Bermudez, R. et al. Compositional and orientational control in metal halide perovskites of reduced dimensionality. Nat. Mater. 17, 900–907 (2018).

    Article  ADS  Google Scholar 

  65. Jeon, N. J. et al. Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells. Nat. Mater. 13, 897–903 (2014).

    Article  ADS  Google Scholar 

  66. Soe, C. M. M. et al. Understanding film formation morphology and orientation in high member 2D Ruddlesden-Popper perovskites for high‐efficiency solar cells. Adv. Energy Mater. 8, 1700979 (2018).

    Article  Google Scholar 

  67. Zhang, X. et al. Phase transition control for high performance Ruddlesden-Popper perovskite solar cells. Adv. Mater. 30, 1707166 (2018).

    Article  Google Scholar 

  68. Venkatesan, N. R., Labram, J. G. & Chabinyc, M. L. Charge-carrier dynamics and crystalline texture of layered Ruddlesden-Popper hybrid lead iodide perovskite thin films. ACS Energy Lett. 3, 380–386 (2018).

    Article  Google Scholar 

  69. Yu, J. C. et al. Improving the stability and performance of perovskite light-emitting diodes by thermal annealing treatment. Adv. Mater. 28, 6906–6913 (2016).

    Article  Google Scholar 

  70. Hamill, J. C. Jr., Schwartz, J. & Loo, Y. L. Influence of solvent coordination on hybrid organic-inorganic perovskite formation. ACS Energy Lett. 3, 92–97 (2018).

    Article  Google Scholar 

  71. Zhao, L. F. et al. In situ preparation of metal halide perovskite nanocrystal thin films for improved light-emitting devices. ACS Nano 11, 3957–3964 (2017).

    Article  Google Scholar 

  72. **ao, Z. G. et al. Engineering perovskite nanocrystal surface termination for light-emitting diodes with external quantum efficiency exceeding 15%. Adv. Funct. Mater. 29, 1807284 (2019).

    Article  Google Scholar 

  73. **ao, Z. G. et al. Efficient perovskite light-emitting diodes featuring nanometre-sized crystallites. Nat. Photonics 11, 108–115 (2017).

    Article  ADS  Google Scholar 

  74. Soe, C. M. M. et al. New type of 2D perovskites with alternating cations in the interlayer space, (C(NH2)3)(CH3NH3)nPbnI3n+1: structure, properties, and photovoltaic performance. J. Am. Chem. Soc. 139, 16297–16309 (2017).

    Article  Google Scholar 

  75. Quan, L. N. et al. Tailoring the energy landscape in quasi-2D halide perovskites enables efficient green-light emission. Nano Lett. 17, 3701–3709 (2017).

    Article  ADS  Google Scholar 

  76. Yantara, N. et al. Designing efficient energy funneling kinetics in Ruddlesden-popper perovskites for high-performance light-emitting diodes. Adv. Mater. 30, 1800818 (2018).

    Article  Google Scholar 

  77. Lei, L. et al. Efficient energy funneling in quasi-2D perovskites: from light emission to lasing. Adv. Mater. 32, 1906571 (2020).

    Article  Google Scholar 

  78. Ban, M. Y. et al. Solution-processed perovskite light emitting diodes with efficiency exceeding 15% through additive-controlled nanostructure tailoring. Nat. Commun. 9, 3892 (2018).

    Article  ADS  Google Scholar 

  79. Quan, L. N. et al. Edge stabilization in reduced-dimensional perovskites. Nat. Commun. 11, 170 (2020).

    Article  ADS  Google Scholar 

  80. Gao, C. C. et al. Multifunctional naphthol sulfonic salt incorporated in lead-free 2D tin halide perovskite for red light-emitting diodes. ACS Photonics 7, 1915–1922 (2020).

    Article  Google Scholar 

  81. Yang, X. L. et al. Efficient green light-emitting diodes based on quasi-two-dimensional composition and phase engineered perovskite with surface passivation. Nat. Commun. 9, 570 (2018).

    Article  ADS  Google Scholar 

  82. Lee, S. et al. Control of interface defects for efficient and stable quasi-2D Perovskite light-emitting diodes using nickel oxide hole injection layer. Adv. Sci. 5, 1801350 (2018).

    Article  Google Scholar 

  83. Wang, Z. B. et al. Manipulating the trade-off between quantum yield and electrical conductivity for high-brightness quasi-2D perovskite light-emitting diodes. Adv. Funct. Mater. 28, 1804187 (2018).

    Article  Google Scholar 

  84. Tian, Y. et al. Highly efficient spectrally stable red perovskite light‐emitting diodes. Adv. Mater. 30, 1707093 (2018).

    Article  Google Scholar 

  85. Meng, F. Y. et al. Co-interlayer engineering toward efficient green quasi-two-dimensional perovskite light-emitting diodes. Adv. Funct. Mater. 30, 1910167 (2020).

    Article  Google Scholar 

  86. Cheng, T. et al. Stoichiometry control for the tuning of grain passivation and domain distribution in green quasi-2D metal halide perovskite films and light-emitting diodes. Adv. Funct. Mater. 30, 2001816 (2020).

    Article  Google Scholar 

  87. Series, B. T. Parameter Values for Ultra-high Definition Television Systems for Production and International Programme Exchange (2012).

  88. Kumar, S. et al. Efficient blue electroluminescence using quantum-confined two-dimensional perovskites. ACS Nano 10, 9720–9729 (2016).

    Article  Google Scholar 

  89. Wang, Q. et al. Efficient sky-blue perovskite light-emitting devices based on ethylammonium bromide induced layered perovskites. ACS Appl. Mater. Interfaces 9, 29901–29906 (2017).

    Article  Google Scholar 

  90. Cheng, L. et al. Sky-blue perovskite light-emitting diodes based on quasi-two-dimensional layered perovskites. Chin. Chem. Lett. 28, 29–31 (2017).

    Article  Google Scholar 

  91. Chen, H. T. et al. Sodium ion modifying in situ fabricated CsPbBr3 nanoparticles for efficient perovskite light emitting diodes. Adv. Optic. Mater. 7, 1900747 (2019).

    Article  Google Scholar 

  92. Chen, P. et al. Charge-transfer versus energy-transfer in quasi-2D perovskite light emitting diodes. Nano energy 50, 615–622 (2018).

    Article  Google Scholar 

  93. Protesescu, L. et al. Nanocrystals of cesium lead halide perovskites (CsPbX3, X= Cl, Br, and I): novel optoelectronic materials showing bright emission with wide color gamut. Nano Lett. 15, 3692–3696 (2015).

    Article  ADS  Google Scholar 

  94. Song, J. Z. et al. Quantum dot light-emitting diodes based on inorganic perovskite cesium lead halides (CsPbX3). Adv. Mater. 27, 7162–7167 (2015).

    Article  Google Scholar 

  95. Li, G. R. et al. Highly efficient perovskite nanocrystal light-emitting diodes enabled by a universal crosslinking method. Adv. Mater. 28, 3528–3534 (2016).

    Article  ADS  Google Scholar 

  96. Dutta, A. et al. Near-Unity photoluminescence quantum efficiency for all CsPbX3 (X= Cl, Br, and I) perovskite nanocrystals: a generic synthesis approach. Angew. Chem. Int. Ed. 58, 5552–5556 (2019).

    Article  Google Scholar 

  97. Li, Z. C. et al. Modulation of recombination zone position for quasi-two-dimensional blue perovskite light-emitting diodes with efficiency exceeding 5%. Nat. Commun. 10, 1027 (2019).

    Article  ADS  Google Scholar 

  98. Vashishtha, P. et al. High efficiency blue and green light-emitting diodes using Ruddlesden-Popper inorganic mixed halide perovskites with butylammonium interlayers. Chem. Mater. 31, 83–89 (2019).

    Article  Google Scholar 

  99. Yao, E. P. et al. High-brightness blue and white leds based on inorganic perovskite nanocrystals and their composites. Adv. Mater. 29, 1606859 (2017).

    Article  Google Scholar 

  100. Vashishtha, P. & Halpert, J. E. Field-driven ion migration and color instability in red-emitting mixed halide perovskite nanocrystal light-emitting diodes. Chem. Mater. 29, 5965–5973 (2017).

    Article  Google Scholar 

  101. Brivio, F., Caetano, C. & Walsh, A. Thermodynamic origin of photoinstability in the CH3NH3Pb(I1-xBrx)3 hybrid halide perovskite alloy. J. Phys. Chem. Lett. 7, 1083–1087 (2016).

    Article  Google Scholar 

  102. Wang, Q. et al. Efficient sky-blue perovskite light-emitting diodes via photoluminescence enhancement. Nat. Commun. 10, 5633 (2019).

    Article  ADS  Google Scholar 

  103. Yuan, Y. B. & Huang, J. S. Ion migration in organometal trihalide perovskite and its impact on photovoltaic efficiency and stability. Acc. Chem. Res. 49, 286–293 (2016).

    Article  Google Scholar 

  104. Ma, D. X. et al. Chloride insertion-immobilization enables bright, narrowband, and stable blue-emitting perovskite diodes. J. Am. Chem. Soc. 142, 5126–5134 (2020).

    Article  Google Scholar 

  105. Zhao, J. J. et al. Strained hybrid perovskite thin films and their impact on the intrinsic stability of perovskite solar cells. Sci. Adv. 3, eaao5616 (2017).

    Article  Google Scholar 

  106. Kubicki, D. J. et al. Cation dynamics in mixed-cation (MA)x(FA)1-xPbI3 hybrid perovskites from solid-state NMR. J. Am. Chem. Soc. 139, 10055–10061 (2017).

    Article  Google Scholar 

  107. Philippe, B. et al. Chemical distribution of multiple cation (Rb+, Cs+, MA+, and FA+) perovskite materials by photoelectron spectroscopy. Chem. Mater. 29, 3589–3596 (2017).

    Article  Google Scholar 

  108. Gao, L. L. et al. Improved environmental stability and solar cell efficiency of (MA, FA) PbI3 perovskite using a wide-band-gap 1D thiazolium lead iodide cap** layer strategy. ACS Energy Lett. 4, 1763–1769 (2019).

    Article  Google Scholar 

  109. Linaburg, M. R. et al. Cs1-xRbxPbCl3 and Cs1-xRbxPbBr3 solid solutions: understanding octahedral tilting in lead halide perovskites. Chem. Mater. 29, 3507–3514 (2017).

    Article  Google Scholar 

  110. Jiang, Y. Z. et al. Spectra stable blue perovskite light-emitting diodes. Nat. Commun. 10, 1868 (2019).

    Article  ADS  Google Scholar 

  111. Lanzetta, L. et al. Two-dimensional organic tin halide perovskites with tunable visible emission and their use in light-emitting devices. ACS Energy Lett. 2, 1662–1668 (2017).

    Article  Google Scholar 

  112. Yuan, F. L. et al. Color-pure red light-emitting diodes based on two-dimensional lead-free perovskites. Sci. Adv. 6, eabb0253 (2020).

    Article  ADS  Google Scholar 

  113. Gauthron, K. et al. Optical spectroscopy of two-dimensional layered (C6H5C2H4-NH3)2-PbI4 perovskite. Opt. Express 18, 5912–5919 (2010).

    Article  ADS  Google Scholar 

  114. Gong, X. W. et al. Electron-phonon interaction in efficient perovskite blue emitters. Nat. Mater. 17, 550–556 (2018).

    Article  ADS  Google Scholar 

  115. Yantara, N. et al. Designing the perovskite structural landscape for efficient blue emission. ACS Energy Lett. 5, 1593–1600 (2020).

    Article  Google Scholar 

  116. **, Y. et al. Synergistic effect of dual ligands on stable blue quasi-2D perovskite light-emitting diodes. Adv. Funct. Mater. 30, 1908339 (2020).

    Article  Google Scholar 

  117. Yuan, S. et al. Optimization of low-dimensional components of quasi-2D perovskite films for deep-blue light-emitting diodes. Adv. Mater. 31, 1904319 (2019).

    Article  Google Scholar 

  118. Leung, T. L. et al. Mixed spacer cation stabilization of blue-emitting n = 2 Ruddlesden-Popper organic-inorganic halide perovskite films. Adv. Optic. Mater. 8, 1901679 (2020).

    Article  Google Scholar 

  119. Chang, J. et al. Enhanced performance of red perovskite light-emitting diodes through the dimensional tailoring of perovskite multiple quantum wells. J. Phys. Chem. Lett. 9, 881–886 (2018).

    Article  Google Scholar 

  120. Ren, Z. W. et al. High-performance blue perovskite light-emitting diodes enabled by efficient energy transfer between coupled quasi-2D perovskite layers. Adv. Mater. 33, 2005570 (2021).

    Article  Google Scholar 

  121. **ng, J. et al. Color-stable highly luminescent sky-blue perovskite light-emitting diodes. Nat. Commun. 9, 3541 (2018).

    Article  ADS  Google Scholar 

  122. Wang, Y. K. et al. Chelating-agent-assisted control of CsPbBr3 quantum well growth enables stable blue perovskite emitters. Nat. Commun. 11, 3674 (2020).

    Article  ADS  Google Scholar 

  123. Yang, Z. Y. et al. Low-dimensionality perovskites yield high electroluminescence. Sci. Bull. 65, 1057–1060 (2020).

    Article  Google Scholar 

  124. Lee, S. J. et al. Versatile defect passivation methods for metal halide perovskite materials and their application to light-emitting devices. Adv. Mater. 31, 1805244 (2019).

    Article  Google Scholar 

  125. Shen, H. B. et al. Visible quantum dot light-emitting diodes with simultaneous high brightness and efficiency. Nat. Photonics 13, 192–197 (2019).

    Article  ADS  Google Scholar 

  126. Chen, Y. N. et al. 2D Ruddlesden-Popper perovskites for optoelectronics. Adv. Mater. 30, 1703487 (2018).

    Article  Google Scholar 

  127. Yu, J. C. et al. Effect of perovskite film morphology on device performance of perovskite light-emitting diodes. Nanoscale 11, 1505–1514 (2019).

    Article  Google Scholar 

  128. Kim, Y. H., Kim, J. S. & Lee, T. W. Strategies to improve luminescence efficiency of metal-halide perovskites and light-emitting diodes. Adv. Mater. 31, 1804595 (2019).

    Article  Google Scholar 

  129. Sum, T. C., Righetto, M. & Lim, S. S. Quo vadis, perovskite emitters? J. Chem. Phys. 152, 130901 (2020).

    Article  Google Scholar 

  130. Liu, X. K. & Gao, F. Organic-inorganic hybrid Ruddlesden-Popper perovskites: an emerging paradigm for high-performance light-emitting diodes. J. Phys. Chem. Lett. 9, 2251–2258 (2018).

    Article  Google Scholar 

  131. Chin, X. Y. et al. Self-assembled hierarchical nanostructured perovskites enable highly efficient LEDs via an energy cascade. Energy Environ. Sci. 11, 1770–1778 (2018).

    Article  Google Scholar 

  132. Gao, L. et al. Efficient near-infrared light-emitting diodes based on quantum dots in layered perovskite. Nat. Photonics 14, 227–233 (2020).

    Article  ADS  Google Scholar 

  133. Yang, X. L. et al. Effects of organic cations on the structure and performance of quasi-two-dimensional perovskite-based light-emitting diodes. J. Phys. Chem. Lett. 10, 2892–2897 (2019).

    Article  Google Scholar 

  134. Qin, C. J. et al. Triplet management for efficient perovskite light-emitting diodes. Nat. Photonics 14, 70–75 (2020).

    Article  ADS  Google Scholar 

  135. Han, D. B. et al. Efficient light-emitting diodes based on in situ fabricated FAPbBr3 nanocrystals: the enhancing role of the ligand-assisted reprecipitation process. ACS Nano 12, 8808–8816 (2018).

    Article  Google Scholar 

  136. Yu, X. C. et al. Tailoring the surface morphology and phase distribution for efficient perovskite electroluminescence. J. Phys. Chem. Lett. 11, 5877–5882 (2020).

    Article  Google Scholar 

  137. Liu, Y. et al. Efficient blue light-emitting diodes based on quantum-confined bromide perovskite nanostructures. Nat. Photonics 13, 760–764 (2019).

    Article  ADS  Google Scholar 

  138. Yantara, N. et al. Regulating vertical domain distribution in Ruddlesden-Popper perovskites for electroluminescence devices. J. Phys. Chem. Lett. 10, 7949–7955 (2019).

    Article  Google Scholar 

  139. Tsai, H. et al. Stable light-emitting diodes using phase-pure Ruddlesden-Popper layered perovskites. Adv. Mater. 30, 1704217 (2018).

    Article  Google Scholar 

  140. Lee, H. D. et al. Efficient Ruddlesden-Popper perovskite light-emitting diodes with randomly oriented nanocrystals. Adv. Funct. Mater. 29, 1901225 (2019).

    Article  Google Scholar 

  141. Zhang, L. Q. et al. Ultra-bright and highly efficient inorganic based perovskite light-emitting diodes. Nat. Commun. 8, 15640 (2017).

    Article  ADS  Google Scholar 

  142. Bi, C. et al. Non-wetting surface-driven high-aspect-ratio crystalline grain growth for efficient hybrid perovskite solar cells. Nat. Commun. 6, 7747 (2015).

    Article  ADS  Google Scholar 

  143. Zhao, B. D. et al. Efficient light-emitting diodes from mixed-dimensional perovskites on a fluoride interface. Nat. Electron. 3, 704–710 (2020).

    Article  Google Scholar 

  144. Wang, K. H. et al. Efficient and color-tunable quasi-2D CsPbBrxCl3-x perovskite blue light-emitting diodes. ACS Photonics 6, 667–676 (2019).

    Article  Google Scholar 

  145. Meng, Y. et al. High performance and stable all-inorganic perovskite light emitting diodes by reducing luminescence quenching at PEDOT: PSS/perovskites interface. Org. Electron. 64, 47–53 (2019).

    Article  Google Scholar 

  146. Zhou, Y. M. et al. Improved efficiency of perovskite light-emitting diodes using a three-step spin-coated CH3NH3PbBr3 emitter and a PEDOT: PSS/MoO3-ammonia composite hole transport layer. Micromachines 10, 459 (2019).

    Article  Google Scholar 

  147. Hong, K. & Lee, J. L. Review paper: recent developments in light extraction technologies of organic light emitting diodes. Electron. Mater. Lett. 7, 77–91 (2011).

    Article  ADS  Google Scholar 

  148. Salehi, A. et al. Recent advances in OLED optical design. Adv. Funct. Mater. 29, 1808803 (2019).

    Article  Google Scholar 

  149. Kim, Y. H. et al. Molecular-scale strategies to achieve high efficiency and low efficiency roll-off in simplified solution-processed organic light-emitting diodes. Adv. Funct. Mater. 30, 2005292 (2020).

    Article  Google Scholar 

  150. Chen, C. W. et al. Optical properties of organometal halide perovskite thin films and general device structure design rules for perovskite single and tandem solar cells. J. Mater. Chem. A 3, 9152–9159 (2015).

    Article  Google Scholar 

  151. Lin, T. A. et al. Sky-blue organic light emitting diode with 37% external quantum efficiency using thermally activated delayed fluorescence from spiroacridine-triazine hybrid. Adv. Mater. 28, 6976–6983 (2016).

    Article  ADS  Google Scholar 

  152. Shi, X. B. et al. Optical energy losses in organic-inorganic hybrid perovskite light-emitting diodes. Adv. Optic. Mater. 6, 1800667 (2018).

    Article  Google Scholar 

  153. Chen, Z. M. et al. Utilization of trapped optical modes for white perovskite light-emitting diodes with efficiency over 12%. Joule https://doi.org/10.1016/j.joule.2020.12.008 (2021).

  154. Motti, S. G. et al. Heterogeneous photon recycling and charge diffusion enhance charge transport in quasi-2D lead-halide perovskite films. Nano Lett. 19, 3953–3960 (2019).

    Article  ADS  Google Scholar 

  155. Stranks, S. D. et al. The physics of light emission in halide perovskite devices. Adv. Mater. 31, 1803336 (2019).

    Article  Google Scholar 

  156. Bi, W. T. et al. Efficient quasi-two-dimensional perovskite light-emitting diodes with improved multiple quantum well structure. ACS Appl. Mater. Interfaces 12, 1721–1727 (2020).

    Article  Google Scholar 

  157. Zou, Y. T. et al. Boosting perovskite light-emitting diode performance via tailoring interfacial contact. ACS Appl. Mater. Interfaces 10, 24320–24326 (2018).

    Article  Google Scholar 

  158. Cho, C. et al. The role of photon recycling in perovskite light-emitting diodes. Nat. Commun. 11, 611 (2020).

    Article  ADS  Google Scholar 

  159. Lu, J. X. et al. Ultrathin PEDOT: PSS enables colorful and efficient perovskite light-emitting diodes. Adv. Sci. 7, 2000689 (2020).

    Article  Google Scholar 

  160. Ziebarth, J. M. et al. Extracting light from polymer light-emitting diodes using stamped bragg gratings. Adv. Funct. Mater. 14, 451–456 (2004).

    Article  Google Scholar 

  161. Cheng, Y. H. et al. Enhanced light outcoupling in a thin film by texturing meshed surfaces. Appl. Phys. Lett. 90, 091102 (2007).

    Article  ADS  Google Scholar 

  162. Koo, W. H. et al. Light extraction from organic light-emitting diodes enhanced by spontaneously formed buckles. Nat. Photonics 4, 222–226 (2010).

    Article  ADS  Google Scholar 

  163. Zou, W. et al. Minimising efficiency roll-off in high-brightness perovskite light-emitting diodes. Nat. Commun. 9, 608 (2018).

    Article  ADS  Google Scholar 

  164. Jiang, Y. Z. et al. Reducing the impact of Auger recombination in quasi-2D perovskite light-emitting diodes. Nat. Commun. 12, 336 (2021).

    Article  Google Scholar 

  165. Warby, J. H. et al. Revealing factors influencing the operational stability of perovskite light-emitting diodes. ACS Nano 14, 8855–8865 (2020).

    Article  Google Scholar 

  166. Shang, Y. Q. et al. Quasi-2D inorganic CsPbBr3 perovskite for efficient and stable light-emitting diodes. Adv. Funct. Mater. 28, 1801193 (2018).

    Article  Google Scholar 

  167. Shang, Y. Q. et al. Highly stable hybrid perovskite light-emitting diodes based on Dion-Jacobson structure. Sci. Adv. 5, eaaw8072 (2019).

    Article  ADS  Google Scholar 

  168. Zhao, L. F. et al. Improved outcoupling efficiency and stability of perovskite light-emitting diodes using thin emitting layers. Adv. Mater. 31, 1805836 (2019).

    Article  Google Scholar 

  169. Babayigit, A. et al. Toxicity of organometal halide perovskite solar cells. Nat. Mater. 15, 247–251 (2016).

    Article  ADS  Google Scholar 

  170. Lu, S. H. et al. Accelerated discovery of stable lead-free hybrid organic-inorganic perovskites via machine learning. Nat. Commun. 9, 3405 (2018).

    Article  ADS  Google Scholar 

  171. Qiu, J. J. et al. Stable, efficient near-infrared light-emitting diodes enabled by α/δ phase modulation. J. Phys. Chem. Lett. 10, 2101–2107 (2019).

    Article  Google Scholar 

  172. Kendall, K. R. et al. Recent developments in oxide ion conductors: aurivillius phases. Chem. Mater. 8, 642–649 (1996).

    Article  Google Scholar 

  173. Chen, J. W. et al. Efficient and bright white light-emitting diodes based on single-layer heterophase halide perovskites. Nat. Photonics https://doi.org/10.1038/s41566-020-00743-1 (2020).

  174. Shen, P. F., Vogt, T. & Lee, Y. Pressure-induced enhancement of broad-band white light emission in butylammonium lead bromide. J. Phys. Chem. Lett. 11, 4131–4137 (2020).

    Article  Google Scholar 

  175. Jamaludin, N. F. et al. White electroluminescence from perovskite-organic heterojunction. ACS Energy Lett. 5, 2690–2697 (2020).

    Article  Google Scholar 

  176. Ye, F. et al. Low-temperature soft-cover deposition of uniform large-scale perovskite films for high-performance solar cells. Adv. Mater. 29, 1701440 (2017).

    Article  Google Scholar 

  177. Chu, S. L. et al. Large-area and efficient perovskite light-emitting diodes via low-temperature blade-coating. Nat. Commun. 12, 147 (2021).

    Article  Google Scholar 

  178. Zhao, X. F. & Tan, Z. K. Large-area near-infrared perovskite light-emitting diodes. Nat. Photonics 14, 215–218 (2020).

    Article  ADS  Google Scholar 

  179. Wang, H. R. et al. A multi-functional molecular modifier enabling efficient large-area perovskite light-emitting diodes. Joule 4, 1977–1987 (2020).

    Article  Google Scholar 

  180. Kim, D. B. et al. Uniform and large-area cesium-based quasi-2D perovskite light-emitting diodes using hot-casting method. Adv. Mater. Interfaces 7, 1902158 (2020).

    Article  Google Scholar 

  181. Spechler, J. A. et al. A transparent, smooth, thermally robust, conductive polyimide for flexible electronics. Adv. Funct. Mater. 25, 7428–7434 (2015).

    Article  Google Scholar 

  182. Li, F. et al. Flexible QLED and OPV based on transparent polyimide substrate with rigid alicyclic asymmetric isomer. Org. Electron. 51, 54–61 (2017).

    Article  Google Scholar 

  183. Yao, H. Y. et al. From a flexible hyperbranched polyimide to a microporous polyimide network: Microporous architecture and carbon dioxide adsorption. Polymer 115, 176–183 (2017).

    Article  Google Scholar 

  184. Bade, S. G. R. et al. Fully printed halide perovskite light-emitting diodes with silver nanowire electrodes. ACS Nano 10, 1795–1801 (2016).

    Article  Google Scholar 

  185. Zhao, L. F. et al. Influence of Bulky organo-ammonium halide additive choice on the flexibility and efficiency of perovskite light-emitting devices. Adv. Funct. Mater. 28, 1802060 (2018).

    Article  Google Scholar 

  186. Liu, Y. et al. Fluorescent microarrays of in situ crystallized perovskite nanocomposites fabricated for patterned applications by using inkjet printing. ACS Nano 13, 2042–2049 (2019).

    Google Scholar 

  187. Jia, S. Q. et al. Highly luminescent and stable green quasi-2D perovskite-embedded polymer sheets by inkjet printing. Adv. Funct. Mater. 30, 1910817 (2020).

    Article  Google Scholar 

  188. Zhang, H. H. et al. A two-dimensional Ruddlesden-Popper perovskite nanowire laser array based on ultrafast light-harvesting quantum wells. Angew. Chem. Int. Ed. 57, 7748–7752 (2018).

    Article  Google Scholar 

  189. Li, M. J. et al. Enhanced exciton and photon confinement in Ruddlesden-Popper perovskite microplatelets for highly stable low-threshold polarized lasing. Adv. Mater. 30, 1707235 (2018).

    Article  Google Scholar 

  190. Liang, Y. et al. Lasing from mechanically exfoliated 2D homologous Ruddlesden-Popper perovskite engineered by inorganic layer thickness. Adv. Mater. 31, 1903030 (2019).

    Article  Google Scholar 

  191. Cui, M. H. et al. Direct observation of competition between amplified spontaneous emission and auger recombination in quasi-two-dimensional perovskites. J. Phys. Chem. Lett. 11, 5734–5740 (2020).

    Article  Google Scholar 

  192. Li, M. L. et al. Amplified spontaneous emission based on 2D Ruddlesden-Popper perovskites. Adv. Funct. Mater. 28, 1707006 (2018).

    Article  Google Scholar 

  193. Qin, C. J. et al. Stable room-temperature continuous-wave lasing in quasi-2D perovskite films. Nature 585, 53–57 (2020).

    Article  ADS  Google Scholar 

  194. Liang, D. et al. Color-pure violet-light-emitting diodes based on layered lead halide perovskite nanoplates. ACS Nano 10, 6897–6904 (2016).

    Article  Google Scholar 

  195. Chen, Z. M. et al. High-performance color-tunable perovskite light emitting devices through structural modulation from bulk to layered film. Adv. Mater. 29, 1603157 (2017).

    Article  Google Scholar 

  196. Ren, Z. W. et al. Hole transport bilayer structure for quasi-2D perovskite based blue light-emitting diodes with high brightness and good spectral stability. Adv. Funct. Mater. 29, 1905339 (2019).

    Article  Google Scholar 

  197. Pang, P. Y. et al. Rearranging low-dimensional phase distribution of quasi-2D perovskites for efficient sky-blue perovskite light-emitting diodes. ACS Nano 14, 11420–11430 (2020).

    Article  Google Scholar 

  198. Shen, Y. et al. Interfacial potassium-guided grain growth for efficient deep-blue perovskite light-emitting diodes. Adv. Funct. Mater. https://doi.org/10.1002/adfm.202006736 (2020).

  199. Zhang, Q. P. et al. Efficient metal halide perovskite light-emitting diodes with significantly improved light extraction on nanophotonic substrates. Nat. Commun. 10, 727 (2019).

    Article  ADS  Google Scholar 

  200. Shen, Y. et al. High-efficiency perovskite light-emitting diodes with synergetic outcoupling enhancement. Adv. Mater. 31, 1901517 (2019).

    Article  Google Scholar 

  201. Jeon, S. et al. Perovskite light-emitting diodes with improved outcoupling using a high-index contrast nanoarray. Small 15, 1900135 (2019).

    Article  Google Scholar 

  202. Zhang, Q. P. et al. Three-dimensional perovskite nanophotonic wire array-based light-emitting diodes with significantly improved efficiency and stability. ACS Nano 14, 1577–1585 (2020).

    Article  Google Scholar 

  203. Liu, X. K. et al. Metal halide perovskites for light-emitting diodes. Nat. Mater. https://doi.org/10.1038/s41563-020-0784-7 (2021).

    Article  Google Scholar 

Download references

Acknowledgements

We acknowledge financial support from the National Natural Science Foundation of China (Nos. 21771114, 91956130) and the Natural Science Foundation of Tian** (18YFZCGX00580). M. Yuan acknowledges financial support from Distinguished Young Scholars of Tian** (No. 19JCJQJC62000).

Author information

Author notes

  1. These author contributed equally: Li Zhang, Changjiu Sun

Authors and Affiliations

  1. Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Renewable Energy Conversion and Storage Center (RECAST), College of Chemistry, Nankai University, 300071, Tian**, People’s Republic of China

    Li Zhang, Changjiu Sun, Tingwei He, Yuanzhi Jiang, Junli Wei, Yanmin Huang & Mingjian Yuan

Authors
  1. Li Zhang
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Changjiu Sun
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Tingwei He
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Yuanzhi Jiang
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Junli Wei
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Yanmin Huang
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Mingjian Yuan
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Mingjian Yuan.

Ethics declarations

Conflict of interest

The authors declare no competing interests.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Zhang, L., Sun, C., He, T. et al. High-performance quasi-2D perovskite light-emitting diodes: from materials to devices. Light Sci Appl 10, 61 (2021). https://doi.org/10.1038/s41377-021-00501-0

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1038/s41377-021-00501-0

  • Springer Nature Limited

This article is cited by