Grain Growth of MAPbI₃ via Diethylammonium Bromide Induced Grain Mergence

Various additives are used to improve the film morphology, crystal quality, and grain size for the sake of enhancing the performance of three-dimensional perovskite solar cells. Although significant enhancement in the performance of devices has been made due to the introduction of additives, an in-depth understanding of the additive-related crystallization kinetics and the growth mechanism is still lacking. Here, the grain growth mechanism of diethylammonium bromide (DABr)-doped MAPbI₃ is investigated using in situ dynamic microscopy techniques. The results reveal that the alkyl chains of DABr restrain the growth of grains of MAPbI₃ during spin-coating, and DABr-induced grain mergence during the annealing process, achieving large grains on the micrometer scale. Meanwhile, the crystallization of MAPbI₃ with DABr is significantly improved and the number of defects is reduced. The solar cell with optimized DABr doping MAPbI₃ as the active layer presents a higher power conversion efficiency (PCE) of 19.58% with a fill factor of 79.81%.