Non-fullerene acceptor engineering with three-dimensional thiophene/selenophene-annulated perylene diimides for high performance polymer solar cells

We report two new propeller-shaped perylene diimide (PDI) acceptors based on tetraphenylethylene (TPE) as the core and flanked with S/Se-fused PDIs, named as TPE-PDI₄-S and TPE-PDI₄-Se. Compared to the sulfur-annulated counterpart, TPE-PDI₄-Se exhibits a blue-shifted absorption spectrum, stronger absorption in the region of 400-600 nm, higher LUMO energy level and twisted molecular geometry. The TPE-PDI₄-Se based device with PBDB-T1 as the donor achieved a power conversion efficiency (PCE) of 7.63% along with a high V_OC of 1.08 V, a J_SC of 10.28 mA cm^-2 and a high fill factor of 68.8%, a 11.4% boost in PCE with respect to the TPE-PDI₄-S based control device (6.85%). The high photovoltaic performance of the TPE-PDI₄-Se based device can be attributed to its relatively high-lying LUMO level, complementary absorption spectra with the donor material, relatively favorable morphology and balanced carrier transport. To the best of our knowledge, a PCE of 7.63% is among the highest values for TPE core-based non-fullerene organic solar cells. Overall, our work provides a simple and effective molecule-designing method to promote the PCE of non-fullerene OSCs.