Efficient Semitransparent Bulk-Heterojunction Organic Photovoltaic Cells With High-Performance Low Processing Temperature Indium–Tin Oxide Top Electrode

Abstract-An efficient semitransparent bulk-heterojunction zinc phthalocyanine (ZnPc): fullerene (C₆₀)-based photovoltaic cell with a transparent cathode of Ag/LiF/indium-tin oxide (ITO) is demonstrated. The top ITO layer serves not only as an index matching layer to enhance the light in-coupling in semitransparent small molecule photovoltaic cells, but also improves current spreading due to its superior optical transparency and high electric conductivity. In order to avoid causing damages to the underlying functional photoactive organic layers, the ITO top electrode was formed at room temperature without intentional heating. Optimization of light distribution in the semitransparent ZnPc:C₆₀ photovoltaic cells was performed using an optical admittance analysis. The performance of the semitransparent organic photovoltaic cells is optimized over the two competing parameter of power conversion efficiency (PCE) and optical transparency. Semitransparent bulk-heterojunction ZnPc:C₆₀ photovoltaic cells with an average transmission of more than 40% in the visible light region and a PCE of ~3.0% measured under simulated AM1.5G illumination of 100 mW/cm² were obtained.