Enhancing Open-Circuit Voltage and Charge Transportation for Ternary Organic Solar Cells With Energy Cascade Double Nonfullerene Acceptors

An effective double nonfullerene acceptors ternary organic solar cell (OSC) was systemically investigated to improve the performance of OSCs by doping higher lowest unoccupied molecular orbital (LUMO) energy level nonfullerene acceptor ITIC-Th into the PBDB-T-SF: IT-4F active layer. Compared with binary OSCs, the power conversion efficiency of the optimal ternary OSCs with 20 wt% ITIC-Th content is improved from 9.84% to 11.0%, which was attributed to simultaneous improvements in the open-circuit voltage (V-oc) and fill factor with a slightly reduction in short-current density (J(sc)). The optimal devices show appropriate cascaded LUMO energy level, small aggregation phases of film morphology and higher hole-electron mobility, which are favorable to charge dissociation and significantly beneficial for efficient charge generation and collection. Moreover, under 20 wt% ITIC-Th, the impedance spectra analysis reveals that the smoother surface of the active layer presents a good Ohmic contact for better charge transportation by establishing more potential pathways.