A New Nonfullerene Acceptor with Suppressed Energy Disorder for High-Efficiency Organic Solar Cells

Energy disorder is an important factor that affects charge transport, recombination, and energy loss in organic solar cells. Here, we designed a ladder-type nonfullerene acceptor and studied the critical role of energy disorder in photovoltaic performance. Taking a typical seven-member fused ring acceptor IT-4F as an example, we replaced its sp3-hybridized bridging carbon atoms and linked bulky groups with triisopropylbenzene-substituted pyrrole units. The newly synthesized acceptor 2,2 '-((2Z,2 ' Z)-((3,9-bis(2butyloctyl)-6,12-bis(2,4,6-triisopropylphenyl)-6,12dihydrothieno[2 '',3 '':4 ',5 ']thieno[2 ',3 ':4,5]pyrrolo[2, 3-f]thieno[2 ',3 ':4,5]thieno[3,2-b]indole-2,8-diyl)bis (methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (TBB) has a redshifted absorption spectrum with upshifted energy levels than those of IT-4F. More importantly, TBB shows more suppressed energy disorder, which leads to enhanced charge mobility and improved luminescence efficiency. Consequently, TBB-based devices obtained a power conversion efficiency of 16.2% with a relatively low nonradiative energy loss (0.22 eV), which exceeds that of IT-4F-based devices (11.5%) and is one of the top values among non-Y6 systems. This work demonstrates that rational molecular design is crucial for the suppression of energy disorder.