Healing the Buried Cavities and Defects in Quasi-2D Perovskite Films by Self-Generated Methylamine Gas
Jifei Wang, Shiqiang Luo, Xianglan Tang, Si Xiao, Zhihui Chen, Shuping Pang, Lin Zhang, Yun Lin, Jun He, Yongbo Yuan
Abstract
Perovskites with grain size comparable to film thickness are intensively pursued for high-efficiency solar cells. Geometrically, large grains with high crystallinity tend to form polyhedral shapes that have difficulty forming compact and smooth films. When quasi-two-dimensional RP perovskite films adopt a downward growth mode, defective contacts tend to form at their bottom interfaces with many nanocavities. This is attributed to the angular growing fronts of RP perovskite grains adopting [111] (or/and [101]) growth directions. Self-generated methylamine gas, by a replacement reaction in solution, is introduced to in situ heal these irregular nanocavities that are deeply buried in perovskite films during crystallization processes. The amount of self-generated methylamine gas should be adequately controlled to avoid the homogeneous nucleation of perovskites from a liquid perovskite-amine intermediate phase, which is a key to avoid ruining the grain size and film composition. This in situ healing strategy offers significantly enhanced charge collection efficiency and device working stability.