Rationalizing device performance of perylenediimide derivatives as acceptors for bulk-heterojunction organic solar cells

This study examines the correlation between the structure of four perylenediimide (PDI) derivatives and their optoelectronic behaviors. Three of them with one, two or four PDI moieties conjugated peripherally to porphyrin core by phenylene linker, denoted as nPDI-ZnP (n = 1,2,4), are investigated as acceptors on the charge transport property and device performance in non-fullerene (NF) bulk-heterojunction (BHJ) organic photovoltaic cells with a commercial polymer PTB7-Th as the donor material. Besides, the parent PDI molecule is studied as a control. Detailed charge carrier transport analysis is carried out on these PTB7-Th: Acceptor BHJs. Among all acceptor molecules, PTB7-Th:4PDI-ZnP film possesses the most desirable transport properties among the NF BHJs, and the best device performance with a power conversion efficiency (PCE) of 8.35%. To quantify the transport behaviors, the charge imbalance factor Delta is introduced to describe the global electron and hole balance in different electric fields. We discover that PTB7-Th:4PDI-ZnP has the least Delta and thereby gives rise to a BHJ cells with the highest fill factor and PCE.