Synthesis and photovoltaic properties of small molecule electron acceptors with twin spiro-type core structure

Abstract

In this work, we have developed two A1-A2-D-A2-A1 type small molecule electron acceptors (DTFBT-1, DTFBT-2) with twin spiro-type core structure as D unit, benzothiadiazole (BT) as A2 unit, 3-ethyl-rhodanine (R) or 2-(1,1-Dicyanomethylene) rhodanine (RCN) as A1 unit. The organic solar cells (OSCs) based on the acceptors DTFBT-1 or DTFBT-2 blended with donor J71 achieved the power conversion efficiency (PCE) of 3.35% and 4.40%, respectively. The twin spiro-type core structure with a good planarity facilitates the stacking of molecules. Especially, DTFBT-1 and DTFBT-2 based devices exhibited a high Voc of 1.15 V and 0.96 V for as-cast film due to the high LUMO of acceptors. DTFBT-2 based device showed a bigger short circuit current density (Jsc) due to the RCN of excellent electron-accepting ability. The results indicate that twin spiro-type core fused side group and the terminal group end-capped are significant strategies to improve the performance of nonfullerene acceptors (NFA) devices.