Controlled-humidity annealing represents a powerful approach to modulate perovskite crystallization and film morphologies, as appropriate moisture facilitates the crystallization process. However, rapid crystallization during thermal annealing often produces randomly oriented films, introducing electronic heterogeneity that compromises the efficiency and stability of perovskite solar cells (PSCs). Herein, a moisture-modulated stepwise temperature annealing (MSTA) strategy is developed to enable good control over the crystallographic orientation of perovskite films, providing an alternative to film orientation regulation that is typically achieved with chemical additives or solvent chemistry engineering. Under varying humidity levels, distinct moisture-coordinated intermediate phases direct preferential (220) and (111) crystal orientations. MSTA-processed, (111)-oriented PSCs achieve a high efficiency of 25.38%, surpassing (220)-oriented counterparts (24.96%) while also demonstrating enhanced device longevity and comparable short-circuit current density. This work provides the potential of moisture-assisted, thermally mediated perovskite crystallization in governing film orientation, offering a promising pathway for air-processing perovskite films toward efficient and durable facet-dependent photovoltaics.
Li et al. (Wed,) studied this question.
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