Controlling Blend Morphology for Ultrahigh Current Density in Nonfullerene Acceptor-Based Organic Solar Cells

In this Letter, we highlight a system with a well-known polymer donor (PTB7-Th) blended with a narrow band gap nonfullerene acceptor (IEICO-4F) as the active layer and 1-chloronaphthalene (CN) as the solvent additive. Optimization of the photoactive layer nanomorphology yields a short-circuit current density value of 27.3 mA/cm2, one of the highest values in organic solar cells reported to date, which competes with other types of solution-processed solar cells such as perovskite or quantum dot devices. Along with decent open-circuit voltage (0.71 V) and fill factor values (66%), a power conversion efficiency of 12.8% is achieved for the champion devices. Morphology characterizations elucidate that the origin of this high photocurrent is mainly the increased π–π coherence length of the acceptor, the domain spacing, as well as the mean-square composition variation of the blend. Optoelectronic measurements confirm a balanced hole and electron mobility and reduced trap-assisted recombination for the best devices.