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Formamidine (FA)-based perovskite has bandgap close to the optimal bandgap of single junction solar cell is gradually attracting more attentions in the community. However, cracks are commonly found in FA-based perovskite films right after the spin-coating at room temperature, which has detrimental effect on the solar cell performance. Cooling down the glovebox temperature has become a general practice to solve this issue, yet the temperature effect on the nucleation and crystallization processes if still unknow. In this work, we developed in-situ photoluminescence and absorption techniques to investigate the temperature effect on the nucleation and crystallization of FA-based perovskite crystals (FAxMA1-xPbI3) during spin-coating and annealing processes. Combining with density functional theory (DFT) results, we have found that FAPbI3 framework is firstly generated, which is then followed by the incorporation of FA, MA, Pb, I ions into crystal lattice. Both the higher FA content and higher temperature would significantly increase the growth rate of perovskite, resulting in phase aggregation and stress relief. Leading to the formation of cracks. This work provides a unique and intuitive perspective towards the understanding of the FA-based perovskite growth mechanism.
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