Enhanced Open‐Circuit Voltage by Using 2,7‐Pyrene as a Central Donor Unit in A‐π‐D‐π‐A‐Type Small‐Molecule‐Based Organic Solar Cells

Abstract To get insights into the relationship between molecular structure and performance in photovoltaic cells, two small molecules of T(3TDRCN) 2 and Pr(3TDRCN) 2 were synthesized with an A‐π‐D‐π‐A type backbone structure. The T(3TDRCN) 2 and Pr(3TDRCN) 2 were using n‐octyl side chains substituted trithiophene (3T) as the π‐linker and 2‐(1,1‐dicyanomethylene)‐rhodanine (DRCN) as terminal acceptor (A) group, while varied the central donor (D) unit from thiophene (T) to 2,7‐pyrene (Pr). Both SMs were applied as donor materials along with fullerene acceptor (PC 71 BM) for solution‐processed bulk‐heterojunction solar cells. The impacts of central donor units on their optical absorption, electrochemical property, hole mobility, and solar cell performance were primarily studied. The T(3TDRCN) 2 :PC 71 BM based devices yielded a power conversion efficiency (PCE) of 2.60 % with an open circuit voltage ( V oc ) of 0.89 V. Interestingly, the Pr(3TDRCN) 2 based solar cell exhibited an higher PCE of 4.47 % with an improved V oc of 0.95 V. Our work indicates that using large π‐conjugated aromatic donor with weak‐electron donating property as central unit can improve V oc , as well as high photovoltaic efficiency of the A‐π‐D‐π‐A type SMs in organic solar cells.