Molecular sublimation enables 2D-3D transformation of orientational FAPbI3 perovskites

The precise alignment and strategic positioning of crystal facets are essential for enhancing the stability and photovoltaic efficacy of perovskite materials. However, the synthesis of preferred facet orientations and the deconstruction of growth mechanisms are challenging due to randomized nucleation upon solvent removal and the consequent uncontrollable crystalline growth in traditional approaches. To mitigate solvent-induced disorder effects, here we introduce an approach involving a two-dimensional (2D) layered perovskite that initiates crystallographically controlled lattice growth upon molecular sublimation. This direct all-solid synthetic pathway is termed '2D-to-3D (alpha)' and complements the traditional 'delta-to-alpha' phase transformation route. The growth of highly oriented alpha-formamidinium lead iodide (alpha-FAPbI3) perovskite films is facilitated, characterized by precise control over facet alignment and minimized lattice mismatch. A solar cell efficiency of 25.01% is achieved and the method offers advantages for the upscaling of perovskite solar cells to module-level manufacturing, demonstrating an efficiency of over 20% for an active area of 70 cm2.