Efficient Perovskite Solar Cells Achieved using the 2-Methoxyethanol Additive: Morphology and Composition Control of Intermediate Film

Achieving a highly crystalized perovskite active layer with a dense, flat surface and a large grain size is very significant for constructing efficient perovskite solar cells (PSCs). Regarding this, the solvent engineering plays an important role in optimizing perovskite crystallinity and the final device performance. 2-Methoxyethanol (2-ME) is recently reported to be a good processing solvent of a high-quality perovskite film. However, in a conventional one-step fabrication method, little attempt is made to introduce 2-ME as a solvent additive into the N,N-dimethylformamide/dimethyl sulfoxide (DMSO)-based perovskite precursor and study its influences on the quality of the resulting perovskite film. In this report, we demonstrate that 2-ME can be a feasible additive to modify the crystallinity of the perovskite active layer. Samples prepared in the presence of 2-ME show larger grains and less grain boundaries repeatedly. 2-ME also rationalizes DMSO in the CH3NH3I–PbI2–DMSO intermediate film effectively, thus guaranteeing a flat and pin-hole-free film at the same time. Lower levels of traps and trap-assisted recombination are confirmed owing to the morphology improvement. The 2-ME-optimized planar devices yield a higher average power conversion efficiency and a better stability under an ambient atmosphere. This work may provide an alternative method to control the perovskite crystal growth and prepare PSCs with a higher performance and stability.