Attaching Electron‐Donating Thiophene Rings on Small Molecule Acceptors for Organic Solar Cells with Ultra‐Low Nonradiative Energy Losses

The high nonradiative energy losses (Δ E nr s) in organic solar cells (OSCs) have become a huge obstacle for further improvements of their power conversion efficiencies (PCEs). To address it, the normal small molecule acceptor (SMA) is modified by attaching thiophene, 2‐methylthiophene, and 2‐chlorothiophene rings, respectively, on the terminals, giving three novel SMAs TIC, MTIC, and CTIC. With gradual increasing in the electron‐donating capabilities of thiophene rings, these SMAs own more and more reduced intramolecular charge transfer (ICT) effects in the order of CTIC > TIC > MTIC. Reversely, the OSCs based on CTIC, TIC, and MTIC exhibit the monotonically increased electroluminescence quantum efficiencies (EQE EL s) of 0.27%, 0.36%, and 0.44%, corresponding to lower and lower Δ E nr s of 0.153, 0.145, and 0.140 eV, respectively. These values are all among the best ones for OSCs to date. Finally, when CTIC is introduced into PM6:BTP‐eC9 binary system, the resulting ternary OSC delivers an improved open‐circuit voltage ( V OC ) of 0.864 V, thereby, a higher PCE of 18.82%. This study demonstrates that weakening ICT effects of SMAs is an effective strategy to realize smaller energy losses for OSCs.