Highly efficient flexible organic photovoltaic modules for sustainable energy harvesting under low-light condition via suppressing voltage-drop by metal-mediated cross-linkable polymer interfacial layer

This study aims to expand the practical applications of large-area flexible organic photovoltaics (OPV), such that they retain their high stability and efficiency even under various weather conditions and external stresses. By developing polyethyleneimine derivative-based cathode interfacial layer (CIL) and non-fullerene acceptor (NFA) material in OPVs, the efficiency and stability decrease rapidly due to an undesirable interaction when these two materials are concomitantly applied. In this study, we designed a novel low-cost metal-mediated cross-linked non-conjugated polymer interfacial layer (c-PEIE) and improved the device performance and stability of flexible OPVs from the cell-to-module scale. c-PEIE CIL based flexible OPV cell achieves one of the highest power conversion efficiencies (PCE) of 16.45% and remarkable photostability, retaining 77.58% of its initial PCE for 110 h under continuous light illumination, while the conventional PEIE based cells realize a PCE of 12.58% and poor device stability. Accordingly, a 50 cm2, large-area, flexible OPV module was also fabricated with an excellent PCE of 13.12% which is ~ 80% as efficient as small-area flexible cells. Notably, c-PEIE based OPV devices maintain high output power on cloudy days, which is a particular point of interest to efficiently harvest sunlight energy constantly. The tunable energy barrier and significant low-leakage current of CIL play a critical role in reducing open-circuit voltage and fill factor losses under low-light environments. Such energy sources can provide power efficiently all day long in low-light or cloudy environments to the Internet of Things wireless networks integrated with battery-independent photovoltaics.