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%.