No abstract

Anti‐solvent assisted crystallization (ASAC) is currently one of the most widely used methods to obtain perovskite films with great quality due to its advantage of low cost and easy operation. The commonly used anti‐solvents, toluene, and chlorobenzene (CB), are well recognized to be contaminants in drinking water and exhibit high toxicity levels. It is desirable to develop environmentally benign solvents for the fabrication of perovskite solar cells by ASAC method. As a green solvent, methoxybenzene (PhOMe) has the advantages of low toxicity, moderate saturated vapor pressure, and similar solvent features with toluene and CB. Here, we report highly efficient planar perovskite solar cells (PSCs) prepared by ASAC method using PhOMe green anti‐solvent, achieving a power conversion efficiency (PCE) of 19.42%, which is better than CB processed PSCs (19.09%). Compared to CB processed perovskite films, perovskites produced by PhOMe exhibit smoother surfaces, larger grains, and lower carrier recombination rates, while the crystallization and absorption features remain basically unchanged. These results demonstrate that PhOMe is an excellent anti‐solvent alternative for high‐quality perovskites and thus provide new opportunities for environmental‐friendly manufacturing of PSCs and other optoelectronic devices.

It is essential to minimize the interfacial trap states and improve the carrier collection for high efficiency perovskite solar cells (PSCs). Herein, we present a facile method to construct a p-type graded heterojunction (GHJ) in normal PSCs by deploying a gradient distribution of hole-transporting materials (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], PTAA, in this case) in the shallow perovskite layer. The formation of the GHJ structure facilitates charge transfer and collection, and passivates interfacial trap states, thus delivering a power conversion efficiency (PCE) of 20.05 % along with steady output efficiency of 19.3 %, which is among the highest efficiencies for cesium formamidinium (Cs-FA) lead halide PSCs. Moreover, the unencapsulated devices based on these (Cs-FA) lead halide perovskites show excellent long-term stability; more than 95 % of their initial PCE can be retained after 1440 h storage under ambient conditions. This study may provide an effective strategy to fabricate high-efficiency PSCs with great stability.