Systematic investigation on stability influence factors for organic solar cells

Degradation of organic solar cells has always hindered the commercialization of organic solar cells (OSCs). In this paper, we fabricate OSCs with a power conversion efficiency (PCE) of 16.20%. The impact of different layers on degradation is studied for the first time by performing accelerated aging test on each layer. The device experiencing accelerated aging process on ITO/ZnO barely decays, indicating the electron transport layer (ETL) ZnO hardly affects the device degradation. The device experiencing accelerated aging process on ITO/ZnO/active layer and the and the device experiencing accelerated aging process on ITO/ZnO/active layer/MoO3 decay fast, manifesting the big impact of active layer and MoO3 on degradation. During the accelerated aging process, the morphology of the active layer changes, hindering light absorption and charge transport. Besides, the work function of hole transport layer (HTL) MoO3 becomes shallower after accelerated aging, making the hole extraction less efficient. Transient absorption spectroscopy (TAS) is recorded to investigate exciton physics change during the accelerated aging process, proving that inefficient charge transfer (CT) state excitons formation and separation account for the PCE decay. The mechanism of the degradation of OSCs is discussed, laying the foundation of their commercialization.