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Phase transition during annealing in the two‐step sequential deposition has drawn intensive attention as its significance in fabricating superior perovskite films. However, previous works have not paid enough attention to the importance of the purified phase transition path in the crystallization process. Herein, different from the mixed paths in the conventional cognition, purified phase transition path for α‐FAPbI3 crystallization is achieved by introducing dimethylurea (DMU) into lead iodide (PbI2) precursor solution. The multifunctional molecule is found to design a penetrable porous PbI2 film and fundamentally regulate the perovskite crystallization by forming single phase transition path via the complete δ‐phase during annealing of perovskite. The role of DMU in purified transition path for α‐FAPbI3 crystallization is unraveled with in situ photoluminescence and grazing incidence wide‐angle x‐ray scattering (GIWAXS) investigation. The crystal quality of perovskite films is significantly improved, resulting in single crystal‐like film. The best‐performing perovskite solar cells (PSCs) deliver a power conversion efficiency of 24.75%, resulting from the higher FF of 83.25% and an improved long‐term stability up to 3600 h. This work highlights the importance of purified phase transition path for the superior crystal quality toward high‐performance perovskite photovoltaics. [ABSTRACT FROM AUTHOR]

The development of perovskite light‐emitting diodes (PeLEDs) with both high efficiency and excellent stability remains challenging. Herein, a strong correlation between the lattice strain in perovskite films and the stability of resulting PeLEDs is revealed. Based on high‐efficiency PeLEDs, the device lifetime is optimized by rationally tailoring the lattice strain in perovskite films. A PeLED with a high peak external quantum efficiency of 18.2% and a long lifetime of 151 h (T70, under a current density of 20 mA cm−2) is realized with a minimized lattice strain in the perovskite film. In addition, an increase in the lattice strain is found during the long‐time device stability test, indicating that the degradation of the local perovskite lattice structure could be one of the degradation mechanisms for long‐term stable PeLEDs. [ABSTRACT FROM AUTHOR]

Although all‐inorganic perovskite solar cells (PSCs) demonstrate high thermal stability, cesium‐lead halide perovskites with high iodine content suffer from poor stability of the black phase (α‐phase). In this study, it is demonstrated that incorporating InCl3 into the host perovskite lattice helps to inhibit the formation of yellow phase (δ‐phase) perovskite and thereby enhances the long‐term ambient stability. The enhanced stability is achieved by a strategy for the structural reconstruction of CsPbI2Br perovskite by means of In3+ and Cl− codoping, which gives rise to a significant improvement in the overall spatial symmetry with a closely packed atom arrangement due to the crystal structure transformation from orthorhombic (Pnma) to cubic (Pm‐3m). In addition, a novel thermal radiation heating method that further improves the uniformity of the perovskite thin films is presented. This approach enables the construction of all‐inorganic InCl3:CsPbI2Br PSCs with a champion power conversion efficiency of 13.74% for a small‐area device (0.09 cm2) and 11.4% for a large‐area device (1.00 cm2). Incorporation of indium(III) chloride is directly shown to induce the structural reconstruction of CsPbI2Br perovskite at the microscopic level, which allows the stabilization of the α‐phase perovskite by means of increasing the structure tolerance factor and decreasing the grain size. Consequently, the square‐centimeter all‐inorganic InCl3:CsPbI2Br perovskite solar cells yield a power conversion efficiency of 11.4% with high stability. [ABSTRACT FROM AUTHOR]