Highly Efficient and Photostable Ternary Organic Solar Cells Enabled by the Combination of Non-Fullerene and Fullerene Acceptors with Thienopyrrolodione-based Polymer Donors.

Two polymer donors, PFBDT-8ttTPD and PClBDT-8ttTPD, consisting of halogenated thiophene-substituted benzo[1,2-:4,5-']dithiophene and alkyl-substituted thieno[3,2-]thiophene linked thieno[3,4-]pyrrole-4,6(5)-dione, were designed and synthesized for the evaluation of photovoltaic performances. The fabricated IT-4F-based organic solar cells (OSCs) exhibited maximum power conversion efficiency (PCE) values of 12.81 and 11.12% for PFBDT-8ttTPD and PClBDT-8ttTPD, respectively. Furthermore, PFBDT-8ttTPD:Y6 showed significantly improved PCE (15.05%) due to the extended light harvesting in the broad solar spectrum, whereas the PClBDT-8ttTPD:Y6 displayed relatively low PCE (10.02%). A ternary system incorporating PCBM as the third component into bulk-heterojuction composites (PFBDT-8ttPTD:non-fullerene) was investigated with the aim of utilizing the advantages of PCBM. As a result, PFBDT-8ttTPD:IT-4F:PCBM exhibited an improved PCE (13.67%) compared to that of the corresponding binary OSC. In particular, ternary OSC of PFBDT-8ttTPD:Y6:PCBM showed outstanding photovoltaic performance (PCE = 16.43%) as well as photostability, retaining approximately 80% of the initial PCE after 500 h under continuous illumination. The introduction of a small amount of PCBM resulted in favorable and dense molecular packing with improved crystallinity as well as enhanced charge carrier mobility for efficient OSC.