Collection optimization of photo-generated charge carriers for efficient organic solar cells

Collection of photo-generated charge carriers is of significance in organic photovoltaic devices. Herein, we focus on systematically exploring the effective methods to improve the charge collection efficiency in organic solar cells based on PBDB-T: ITIC. In the active layer, we observe that the energy level bending at the interface of acceptor/donor is influential to the recombination of charge carriers. For extracting electrons efficiently, we propose that using SnO₂ instead of ZnO as the electron conducting layer is advantageous in improving short-circuit current (J_sc), power conversion efficiency (PCE), and particularly stability. To unveil the dynamics of hole collection, we use different metals as the anode and find out that enlarging the work function of the anode close to the highest occupied molecular orbital (HOMO) of the donor is beneficial for enhancing the open-circuit voltage (V_oc), J_sc, fill factor (FF) and thus PCE. The optimized device delivers a PCE of 10.77%. Insights on how to efficiently extract photo-generated charge carriers are elaborated systematically.