LAUSR

Abstract In this work, we design and synthesize three asymmetric acceptor-donor-acceptor (A-D-A) type nonfullerene acceptors (ITOTC, ITUTC and ITUIC) using a novel indenothienothiophene-based unfused core together with two different electron-deficient terminal units (2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene)malononitrile for ITOTC and ITUTC, and 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile for ITUIC). Alkyl chains with different lengths are incorporated in the indenothienothiophene-based unfused core to ensure the good solubility of the resulting nonfullerene acceptors (n-octyl for ITOTC, n-undecyl for ITUTC and ITUIC), and to tune their charge transporting properties as well. Photovoltaic properties of these nonfullerene acceptors are investigated by using a typical wide band-gap polymer of PBDB-T as the donor material. The best-performance polymer solar cell based on ITOTC: PBDB-T with annealing shows a power conversion efficiency (PCE) of 8.35%, in comparison with the counterpart based on ITUTC:PBDB-T which shows a PCE of 7.68%. However, 7.68% PCE is higher than that of the best-performance PSC based on ITUIC:PBDB-T (6.45% PCE). These results suggest that both side-chains and electron-deficient terminal groups can be optimized to improve the photovoltaic properties of A-D-A type nonfullerene acceptors based on the indenothienothiophene-based unfused core.