Low-Temperature Processed Hybrid Organic/Silicon Solar Cells with Power Conversion Efficiency up to 6.5%

Abstract

Hybrid organic/silicon heterostructures have become of great interest for photovoltaic application due to their promising features (e.g. easy fabrication in a low-temperature process) for cost-effective photovoltaics. This work is focused on solar cells with a hybrid heterojunction between the polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) and n-doped monocrystalline silicon. As semi-transparent top contact, a thin (15 nm) Au layer was employed. Devices with different P3HT thicknesses were processed by spin-casting and compared with a reference Au/n-Si Schottky diode solar cell.

The current density-voltage (J-V) measurements of the hybrid devices show a significant increase in open-circuit voltage (V_OC) from 0.29 V up to 0.50 V for the best performing hybrid devices compared to the Schottky diode reference, while the short-circuit current density (J_SC) does not change significantly. The increased V_OC indicates that P3HT effectively reduces the reverse electron current into the gold contact. The wavelength-dependent J_SC measurements show a decreased J_SC in the wavelength range of P3HT absorption. This is related to the reduced J_SC generation in silicon not being compensated by J_SC generation in P3HT. It is concluded that the charge generation in P3HT is less efficient than in silicon.

After a thermal annealing of the hybrid P3HT/silicon solar cells, we achieved power conversion efficiencies (PCE) (AM1.5 illumination) up to 6.5% with V_OC of 0.52 V, J_SC of 18.6 mA/cm² and a fill factor (FF) of 67%. This is more than twice the efficiency of the reference Schottky diode.