摘要： The grain boundaries of perovskite polycrystalline are regarded as a defect region that not only provides carrier recombination sites but also introduces device degradation pathways. Efforts to enlarging the grain size of perovskite film and reducing its grain boundary are crucial for highly efficient and stable PSCs. Some effective methods that facilitate grain growth are post-deposition thermal annealing and solvent vapor annealing. However, a detailed understanding of grain growth mechanisms in perovskite films is lacking. In this study, perovskite films were prepared by adding ethylamine hydrochloride (EACl) to the precursor solution. This additive strategy promotes a new grain growth mode, secondary grain growth, in perovskite films. Secondary grain growth leads to much larger grains with high crystallographic orientation. These excellent properties lead to reduced grain boundaries and the densities of boundary defects. The improved film quality results in a prolonged charge–carrier lifetime and a significantly enhanced PCE. Compared with the PCE 18.42% of the control device, the PCE of the device with EACl additives reaches 21.07%.