Annealing-free perovskite films based on solvent engineering for efficient solar cells

Abstract

One of the main issues for high-performance perovskite solar cells (PSCs) is the fabrication of high-quality perovskite films. However, a thermal annealing process is generally required for a high crystallinity film via a typical solution-based method, which may result in inhomogeneous nucleation, and is time-consuming. Herein, we investigate the effects of different solvents on the morphology and the crystallinity of perovskite films systematically and further develop a solvent-technique for uniform perovskite films without the need for annealing. N-Methyl-2-pyrrolidone (NMP) has been adopted as a high-boiling-point solvent and a complexant, combined with the commonly used N,N-dimethylformamide (DMF) or dimethylacetamide (DMAc), to improve the quality of perovskite films and enhance the corresponding device performance. PSCs fabricated from DMAc/NMP co-solvents using the post-annealing process show the best power conversion efficiency (PCE) of 17.38%, which is about 10% improvement compared to that of the device based on DMF/dimethyl sulfoxide (DMSO) or DMAc/DMSO co-solvents. Notably, 17.09% efficiency has been achieved even without any post-annealing process for the device based on DMAc/NMP co-solvents. However, only 3.81% efficiency can be obtained for the device based on DMAc/DMSO co-solvents under the same conditions. The observed phenomenon is mainly due to the fact that the NMP-included solvents can induce an instant crystallization once the anti-solvent drips on the films at room temperature (RT). Our study may provide a new approach to prepare high-quality perovskite films at RT, which would simplify the fabrication procedures and reduce the cost of efficient PSC manufacture.