Suppression of Time-Dependent Donor/Acceptor Interface Degradation by Redistributing Donor Charge Density

Poor operation stability is a major hurdle for the wide application of organic photovoltaic (OPV) devices. While most attention is given to environmental threats to device stability, we herein show evidence from X-ray photoemission spectroscopy (XPS) of an intrinsic time-dependent chemical reaction at a donor/acceptor interface. Albeit with impressive device performance from boron subphthalocyanine chloride (SubPc)/fullerene (C₆₀) interface, the forming boride bonds at its interface hinders the interfacial exciton dissociation and leads to device deterioration. Due to the high electron affinity of molybdenum oxide (MoO₃) film, the incorporation of MoO₃ layer under the SubPc film has strong electron-drawing property and leads to charge-transfer complex (CTC) formation at the MoO₃/SubPc interface. The resulting charge redistribution in SubPc molecules effectively suppresses the further interfacial reaction at SubPc/C₆₀ junction. Our results provide insight for new degradation mechanisms of OPV devices and corresponding stability control via charge redistribution in the donor film. The poor stability of a SubPc/C₆₀ solar device is shown by XPS analysis to be caused by a time-dependent chemical reaction at the donor/acceptor interface. A simple and effective solution to suppress such reaction is demonstrated by direct charge manipulation of SubPc donor using nano-island structured molybdenum oxide features.