All-Inorganic Cesium-Based Hybrid Perovskites for Efficient and Stable Solar Cells and Modules

In the last ten years, organic–inorganic hybrid perovskites have been skyrocketing the field of innovative photovoltaics (PVs) and now represent one of the most promising solution for next-generation PVs. Within the family of halide perovskites, increasing attention has been focused on the so-called all-inorganic group, where the organic cation is replaced by cesium, as in the case of CsPbI3. This subclass of halide perovskites features desirable optoelectronic properties such as easily tunable bandgap, strong defect tolerance, and improved thermal stability compared to the hybrid systems. When integrated in PV cells, they exhibit high power conversion efficiency (PCE) with record values of 19.03%. However, all-inorganic perovskite solar cells (PCSs) face several challenges such as i) instability of the CsPbI3 photoactive phase in ambient conditions, ii) inhomogeneous film morphology, and iii) high surface defect density. This work focuses on the mentioned challenges with a special attention on discussing the Cs–Pb–X system (X = I, Br). Then, the most recent and effective approaches for increasing both the PCE and the stability of devices are reviewed, which include material doping, interface engineering, and device optimization. Finally, the first efforts toward the upscaling of Cs-based PSCs, and predicted methods for enabling large-scale production, are discussed.