Design and synthesis of medium-bandgap small-molecule electron acceptors for efficient tandem solar cells

Abstract

Medium-bandgap small-molecule acceptors including YITI-0F, YITI-2F, and YITI-4F with a thiophene π-bridge are designed and synthesized. The PBDB-T:YITI-2F-based device shows the best photovoltaic performance with a PCE of up to 10.05%, a V_oc of 0.93 V, a J_sc of 15.54 mA cm⁻² and a FF of 69%. Tandem devices are fabricated by applying it as a front cell and the PTB7-Th:ATT-2-based device as a rear cell, giving a high PCE up to 11.86%.