Highly electronegative additives suppress energetic disorder to realize 19.19 % efficiency binary organic solar cells

Abstract

Additive engineering plays an important role in realizing high efficiency organic solar cells (OSCs). The introduction or residual of additives usually increases the energetic disorder of the active layer, which in turn causes a significant reduction of the open-circuit voltage (VOC). Herein, this work proposes a novel additive design approach, that is, using the highly electronegative groups trifluoromethyl and trifluoromethoxy to replace one bromine atom of 1,3,5-tribromobenzene (TBB) to obtain 3,5-Dibromobenzotrifluoride (DBTF) and 3,5-Dibromo-triffluoromethoxybenzene (DBOF). This series of additives can induce strong π-π coupling with acceptor, modulating molecular crystallization and orderly stacking, and thus reducing the non-radiative energy loss and energetic disorder of the OSCs. Furthermore, DBTF and DBOF have good volatility and can be removed from the active layer without any post-processing. Consequently, a high power conversion efficiency (PCE) of 18.78 % is obtained in D18: Y6-based OSCs and a remarkable PCE of 19.19 % is realized in D18-Cl/ Y6-based OSCs. Compared with the OSCs without or with conventional TBB additives, the DBOF-treated OSCs effectively suppress the reduction of VOC while enhancing PCE. This work provides guidance for the design and synthesis of additives with selectivity, auto-removability, and the ability to reduce the energetic disorder of the OSCs.