Light radiation annealing enables unidirectional crystallization of vacuum-assisted Sn-Pb perovskites for efficient tandem solar cells

Vacuum-assisted technology, favored for its low cost, environmental friendly nature, and scalability, is widely used in perovskite solar cells and is a preferred choice for commercialized production. However, strong solvent extraction at the interface between the wet film and the vacuum causes a thin perovskite film at the top surface and a residual solvent at the buried interface, which results in film stratification and buried voids. Consequently, the efficiency of vacuum-assisted Sn-Pb perovskite solar cells remains below 20%. Herein, we propose a light radiation annealing technique with rapid top-down heating to achieve unidirectional nucleation and growth, which effectively suppresses film stratification and buried voids. This approach yields Sn-Pb perovskite films with a more uniform composition and fewer defects. Based on the optimized films, we achieve a record efficiency of 22.31% among all the vacuum-assisted Sn-Pb perovskite solar cells. Moreover, we obtain an impressive efficiency of 27.62% for all-perovskite tandem solar cells.