Organic photovoltaic cells offer ultrahigh VOC of ∼ 1.2 V under AM 1.5G light and a high efficiency of 21.2 % under indoor light

Abstract

As an emerging classic p-type photovoltaic polymer, D18 has been combined with many Y-series narrow-bandgap (NBG) nonfullerene acceptor (NFAs) and realized over 18 % power conversion efficiency (PCE). Nonetheless, due to the lack of appropriate wide-bandgap (WBG) NFAs, it is difficult for D18 to realize high open circuit voltage (VOC), which also hinders the application of indoor organic photovoltaics (OPVs). Herein, we combined D18 with three benzotriazole (BTA)-based WBG NFAs (BTA5, F-BTA5, and Cl-BTA5) and obtained ultrahigh VOCs of 1.16–1.25 V under AM 1.5G illumination. The gradual increase in PCEs from BTA5 (7.8 %) to F-BTA5 (10.9 %) to Cl-BTA5 (12.0 %) indicated that both fluorination and chlorination are effective strategies to modulate the optoelectronic properties and improve the photovoltaic performance for A2-A1-D-A1-A2 type NFAs. The PCE of 12.0 % for D18: Cl-BTA5 combination is one of the highest values for high-voltage (∼1.2 V) OPVs, which can be attributed to the highest absorption coefficient and the maximum exciton dissociation driving force. In addition, the large area (1.0 cm2) indoor OPV based on D18: Cl-BTA5 realized a PCE of 21.2 % under a light intensity of 1000 lux (2700 K) LED illumination. In summary, our findings have filled the gap in D18-based high VOC (∼1.2 V) and high-efficiency (∼12 %) OPVs, and also proved D18 has great potential for indoor OPV application.