Molecular Electron Acceptor Designed by Modulating Quinoidal-Resonance Effect for Organic Solar Cell Application

In this work, two new low-bandgap electron acceptors NITI-SeS and NITI-SSe that use electron-rich 2-alkylselenopheno[3,4-b]thiophene and 2-alkylselenopheno[2,3-c]thiophene with different quinoidal-resonance effect as π-bridges to link the weak electron-donating indenoindene core and the strong electron-accepting INCN-2F terminal are designed and synthesized. NITI-SeS that has a selenium atom in the main ring shows an obviously redshift absorption, leading to a low optical bandgap of 1.46 eV in thin film. By matching two acceptors with the polymer donor PBDB-T, the NITI-SSe-based device delivered a higher PCE of 12.49% with an open-circuit voltage of 0.91 V, a short-circuit current of 19.41 mA cm−2, and a fill factor of 0.70. This work reveals a convenient but effective method to finely tune the bandgap of non-fullerene acceptors for high-efficiency OSCs.