<i>In situ</i> active guanidinium salts interaction promotes facet orientation and crystallization for efficient and stable inverted perovskite solar cells

Abstract The disordered crystal growth and undesired degradation of perovskite films limit the further improvement of perovskite solar cells (PSCs) performance and their commercialization. Herein, an in situ modulation strategy is proposed for preparing high-quality and stable perovskite films by adjusting phase transformation kinetics. Benefiting from the in situ reaction between the chloroformamidinium hydrochloride (ClFACl) and FA cations, the impurity intermediate phase in the perovskite film is inhibited and the α -FAPbI 3 phase is induced to grow along a preferred (001) orientation. Furthermore, the introduction of ClFACl and the in situ formation of guanidinium salts (FA–Gua) strengthen the intermolecular interactions in the interior regions of crystals, restraining the α -phase degradation of the as-prepared perovskite films under humid and thermal treatments. With crystal orientation optimization and defects reduction, the PSCs with in situ formed FA–Gua yields a champion efficiency of 25.85% and demonstrates excellent phase stability under long-term thermal and humid aging conditions. This in situ chemical modulation strategy expands the avenue toward the optimization of crystallization orientation and α -phase stabilization, promoting the development of PSCs with enhanced performance and stability.