Pyridine-assisted solvent engineering for high-quality narrow-bandgap perovskites in efficient tandem modules

All-perovskite tandem photovoltaic modules represent a promising technology for enhancing power conversion efficiency. However, a significant challenge remains in preparing high-quality, large-area tin-lead mixed narrow-bandgap (NBG) perovskite films for these tandem modules. Here, we develop a method to prepare large-area, compact, and uniform NBG perovskite films by modulating the crystallization process through solvent engineering. Specifically, we introduce pyridine, a solvent with strong donor coordinating ability and high saturated vapor pressure, into the solvent system. The strong coordination ability of pyridine facilitates better formation of intermediate phases during the crystallization process of tin-based NBG perovskite films, while its high saturated vapor pressure enables the solvent to evaporate quickly and reduce solvent residue at the bottom of the films. By combining this strategy with a vacuum annealing method, the all-perovskite tandem photovoltaic mini-modules exhibited an average efficiency of 22.0 ± 0.4% with an aperture area of 10.4 cm2, demonstrating their promising potential for future commercialization.