The study reports the development of highly efficient and thermodynamically stable β-CsPbI3-based perovskite solar cells (PSCs) with efficiencies exceeding 18%. The researchers achieved this by fabricating highly crystalline β-CsPbI3 films with extended spectral response and enhanced phase stability. Synchrotron-based x-ray scattering confirmed the presence of highly oriented β-CsPbI3 grains, and elemental analyses confirmed their all-inorganic composition. To mitigate the effects of cracks and pinholes in the perovskite layer, the team treated the material with choline iodide (CHI), which improved charge carrier lifetime and energy level alignment between the β-CsPbI3 absorber layer and carrier selective contacts. The resulting PSCs showed high reproducibility and stability, achieving an efficiency of 18.4% under ambient conditions.The study reports the development of highly efficient and thermodynamically stable β-CsPbI3-based perovskite solar cells (PSCs) with efficiencies exceeding 18%. The researchers achieved this by fabricating highly crystalline β-CsPbI3 films with extended spectral response and enhanced phase stability. Synchrotron-based x-ray scattering confirmed the presence of highly oriented β-CsPbI3 grains, and elemental analyses confirmed their all-inorganic composition. To mitigate the effects of cracks and pinholes in the perovskite layer, the team treated the material with choline iodide (CHI), which improved charge carrier lifetime and energy level alignment between the β-CsPbI3 absorber layer and carrier selective contacts. The resulting PSCs showed high reproducibility and stability, achieving an efficiency of 18.4% under ambient conditions.