Effect of Benzene Rings’ Incorporation on Photovoltaic Performance of Indacenodithiophene‐cored Molecular Acceptors

Two simple molecular acceptors, NIDBT and NIDT, bearing the same end groups of 2‐(3‐ oxo ‐2,3‐dihydro‐1 H ‐inden‐1‐ylidene)malononitrile (INCN) yet with different core units, indenofluorenodithiophene (IDBT) and indaceno[2,1‐ b :6,5‐ b’ ]dithiophene (IDT), respectively, were adopted to fabricate polymer solar cells by blending with a narrow bandgap polymer donor, PBDBTBTT‐Hex (P3). The incorporation of benzene rings into the molecular skeletons generates a negative effect on the photovoltaic performance of resultant molecular acceptor, rendering an inferior power conversion efficiency of 2.45%, compared to 4.05% for the NIDT‐based bulk‐heterojunction solar cells. Detailed comparison on photovoltaic parameters indicates that the fusion by incorporating two separated benzene rings into the IDT core renders molecular acceptor of weakened intermolecular interaction with the polymer donor, which results in over‐aggregated phase separation, unbalanced charge transport, and serious recombination within the photovoltaic devices. The work contributes to a deep understanding of the effect of skeleton‐fusion strategy for designing high‐performance molecular acceptors.