Insights into the photovoltaic mechanism of organic photovoltaics under solar and artificial light

Abstract

Indoor organic photovoltaics (OPVs) have attracted a lot of attention due to their low energy consumption for applications such as Internet of Things (IoT) and wearable technology. However, the mechanisms influencing the indoor power conversion efficiency (PCE) of OPVs are not very well understood. In this study, we investigated how the active layer based on different acceptor materials, fullerene and non-fullerene, affects the performance of the device. Under indoor light, the optimal thickness of non-fullerene-based OPVs (PBDB-T:ITIC) is 140 nm with a PCE of 19.74% and the optimal thickness of fullerene-based OPVs (PBDB-T:PC₇₁BM) is 100 nm with a PCE of 16.22%. Our study systematically investigated the electrical performance and carrier behavior of different active layers under two light sources (1-Sun and indoor light). We found that the indoor PCE of the non-fullerene system is less affected by the thickness, mainly because the thicker non-fullerene active layer film still maintains good series resistance (R_s), shunt resistance (R_sh), and less charge recombination. Our study points out that the key factors affecting the indoor PCE of OPVs are R_sh, monomolecular recombination, and trap depth, revealing new insights into achieving high indoor PCE of OPVs.