Achieving High External Quantum Efficiency for ITIC-Based Organic Solar Cells with Negligible Homo Energy Offsets

Minimizing energy loss in organic solar cells (OSCS) is critical for attaining high photovoltaic performance. Among the parameters that correlated to photovoltaic performance, the energy offsets between donor-acceptor pairs play a vital role in photoelectric conversion processes. For so far reported a large number of non-fullerene acceptors (NFAs), only Y6 and its derivatives can achieve external quantum efficiencies (EQEs) over 80% with negligible energy offsets when combined with polymeric donors. Thus, understanding the relationship between energy offsets and energy losses in representative NFAs is the key to further enhancing the efficiency of OSCs. In this study, a series of wide-bandgap polymer donors based on pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione (TzBI) and benzo[1,2-c:4,5-c '] dithiophene-4,8-dione building blocks are combined with representative NFAs, including ITIC and Y6, to gain deep insights into their photovoltaic performances and related energy losses. Outstanding EQEs (approximate to 70%) and suppressed non-radiative recombination are achieved at negligible energy offsets. Moreover, it is noted that a prolonged exciton lifetime of acceptor is not essential to obtain high EQEs in OSCs with negligible energy offsets. Eventually, ITIC derivatives with high electroluminescence efficiencies and near-infrared absorptions have the potential to be assembled to obtain high-efficiency OSCs. Various combinations of polymer donors and non-fullerene acceptors (NFAs) are studied to establish the relationship between HOMO energy offset and external quantum efficiency (EQE) of organic solar cells (OSCs). It finds that a prolonged exciton lifetime of NFAs is not the decisive factor to obtain high EQEs for OSCs with negligible HOMO energy offsets.image