This review provides an overview of the growth of perovskite single crystals and their recent development in X-ray detectors.

Controlling the surface traps in metal halide perovskites (MHPs) is essential for device performance, stability, and commercialization. Here, a facile approach is introduced to passivate the methylammonium lead iodide (MAPbI₃) perovskite single crystal (PSC) surface defects by benzylamine (BA) ligand treatment, and the natural crystallographic (100) facets surface of PSC is chosen as the research platform to provide a deeper understanding of the passivation process. The confocal photoluminescence (PL) results show that the pristine three-dimensional (3D) MAPbI₃ PSC surface with a symmetric emission spectrum is normally converted to a pure two-dimensional (2D) BA₂PbI₄, and also forms a quasi-2D Ruddlesden–Popper perovskite (RPP) BA₂MA_n−1PbnI_3n+1 (n = 2, 3, 4, … ∞) after BA exchange with cation defects. The blue shift in the PL peak, as well as the extended exciton lifetimes of time-resolved photoluminescence (TRPL), indicate the realization of surface defect passivation. Additionally, changes in surface morphology are also investigated. The reaction starts with the formation of small, layered crystallites over the surface; as time elapses, the layered crystallites spread and merge in contact with each other, eventually resulting in smooth features. Our findings present a simple approach for MAPbI₃ PSC surface defect passivation, which aims to advance MHP optimization processes toward practical perovskite device applications.

The phase transition of MAPbI3 during the annealing process has been extensively reported, but there is a lack of research on the preformation of resulting perovskite solar cells (PSCs). Here, we systematically investigated the impact of annealing temperature on the crystal structure of MAPbI3. Our findings reveal that an optimal annealing temperature of 100°C yields high crystallinity and a mixture of tetragonal and cubic phases. Deviating from this temperature range results in incomplete conversion to perovskite material at lower temperatures or formation of only cubic crystal structure above 100°C, leading to degradation at higher temperatures. Theoretical calculations also indicate that the conduction band energy level for the cubic phase is approximately 154 meV lower than that for the tetragonal phase, creating an electron extraction barrier between perovskite and TiO2. Solar cells fabricated with mixed-phase films annealed at 100°C exhibit superior performance with a conversion efficiency of 22.01%, attributed to both energetically favourable crystal structure and excellent crystallinity.