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An Electron Acceptor Analogue for Lowering Trap Density in Organic Solar Cells

Typical organic semiconductor materials exhibit a high trap density of states, ranging from 1016 to 1018 cm−3, which is one of the important factors in limiting the improvement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). In order to reduce the trap density within OSCs, a new strategy to design and synthesize an electron acceptor analogue, BTPR, is developed, which is introduced into OSCs as a third component to enhance the molecular packing order of electron acceptor with and without blending a polymer donor. Finally, the as‐cast ternary OSC devices employing BTPR show a notable PCE of 17.8%, with a low trap density (1015 cm−3) and a low energy loss (0.217 eV) caused by non‐radiative recombination. This PCE is among the highest values for single‐junction OSCs. The trap density of OSCs with the BTPR additives, as low as 1015 cm−3, is comparable to and even lower than those of several typical high‐performance inorganic/hybrid counterparts, like 1016 cm−3 for amorphous silicon, 1016 cm−3 for metal oxides, and 1014 to 1015 cm−3 for halide perovskite thin film, and makes it promising for OSCs to obtain a PCE of up to 20%.