Binary Additive–Induced Performance Improvement of PM7:PC71BM Organic Solar Cells with High Open‐Circuit Voltage and Enhanced Current Intensity

Abstract

Adding a solvent additive into the active layer is a simple and effective strategy to improve active layer morphology and performance of bulk heterojunction organic solar cells (OSCs). Herein, poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl‐3‐chloro)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione)] (PM7) is used as donor and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) as acceptor, and 1,8‐diiodooctane (DIO) and 1‐chloronthalene (CN) are utilized as solvent additives to prepare OSCs. The impact of binary additives on the photoelectric performance of OSCs is studied. The binary additives restrict charge recombination and improve carrier mobility effectively, which is proved by the transient photovoltage/transient photocurrent measurement and photoinduced charge carrier extraction by linearly increasing the voltage technology. With the synergetic effect of DIO and CN, the binary additive devices exhibit a high open‐circuit voltage of 0.96 V. Apart from the improved short‐circuit current density and fill factor, the power conversion efficiency reaches to 9.85%, much higher than that of the pristine device without additive (3.79%).