Optical Analysis for Semitransparent Organic Solar Cells

Semitransparent organic solar cells (STOSCs) show great potential for application as power generating windows for buildings. The power conversion efficiency (PCE) and the average visible transmittance (AVT) are both important parameters with which to evaluate the overall performance of STOSCs. However, it is very challenging to simultaneously improve these two performance parameters because they are intrinsically contradictory to each other. In this work, the optical and photovoltaic properties of STOSCs are investigated based on two model samples including PTB7-Th:PC61BM and PTB7-Th:PC71BM by systematically tuning their device structures. By combining optical modeling and experimental results, a full optical analysis is provided for the STOSCs with details on photon harvesting, optical losses, transmission properties, energy distribution spectrum, electric field intensity distribution, and photon absorption rate distribution within the devices. Defined as the sum of the external quantum efficiency and the transmittance, the term quantum utilization efficiency is used as a subjective parameter to describe the light energy use in the semitransparent devices, which provides an alternative angle for analyzing STOSCs.