Photophysics of Solution-Processed Transparent Solar Cells Under Top and Bottom Illumination

Semitransparent organic bulk-heterojunction solar cells based on poly(3-hexylthiophene) (P3HT):phenyl-C -butyric acid methyl ester (PCBM) with a bottom indium tin oxide (ITO) and semitransparent top metal electrode are presented. The solar cell devices are characterized under two different conditions-top illumination and bottom illumination. The photovoltaic performance is compared with a bottom-illuminated reference device having a fully reflecting aluminum electrode. Optical simulations based on the transfer matrix approach were performed in order to understand the device physics of these semitransparent solar cells. We found that unlike bottom illumination, the exciton generation in top-illuminated devices takes place close to the metal electrode giving rise to high recombination losses in such devices.