Evaluation of front and backside performances of a large surface organic photovoltaic module under bifacial illumination

Abstract

Semitransparency is one of the attractive characteristics of thin-film solar modules as it allows electricity generation while providing building illumination. However, enhancing transparency can result in lower energy generation efficiency. An effective way to improve energy production in semitransparent modules is through bifacial illumination. This work aims to evaluate, experimentally, and discuss the optical and electrical properties of a commercial, semitransparent organic photovoltaic (OPV) module under bifacial illumination. With that purpose, current-voltage characteristic curves were obtained under the following conditions: a) front, b) rear illumination and c) simultaneous illumination on both faces. The module was placed inside a V-trough cavity to implement electrical measurements with the module's both faces simultaneously illuminated by natural sunlight. Results show that bifacial illumination is an effective way to enhance energy production in semitransparent OPV devices, and a 46% increase in power generation compared to traditional illumination (frontal illumination) was achieved in the experiments. The backside illumination performance differs by over 40%, compared with the front side, due to electrode shading, optics, and differences in the energy conversion processes taking place in the active layer. The OPV module operation under bifacial illumination is equivalent to a parallel connection between the front and backside illumination performances. Optical modeling shows that the active layer absorbs a large part of the incoming light within the cell spectral response. Nevertheless, in the case of frontal illumination, a significant fraction of solar radiation in the visible region is transmitted and remains available, for instance, for building illumination purposes.