This review gives a full-scale and in-depth summary of CsPbI₂Br perovskite materials for the photovoltaic applications.

Inorganic halide perovskites have attracted significant attention in the field of photovoltaics (PV) in recent years due to their superior intrinsic thermal stability and excellent theoretical power conversion efficiency (PCE). CsPbI₃ with a bandgap of ∼1.7 eV is considered to be the most potential candidate for PV application. However, bulk CsPbI₃ films exhibit poor phase stability. The substitution of some iodide ions with bromide/chloride in CsPbI₃ results in the formation of mixed-halide CsPbX₃ perovskites, which exhibit a good balance between phase stability and efficiency. The halogen-tunable mixed-halide inorganic perovskites have a bandgap matching the sunlight region and show great potential for application in multi-junction tandem and semitransparent solar cells. Herein, the progress of mixed-halide CsPbX₃ PSCs is systematically reviewed, including CsPbI_xBr_yCl_3−x−y- and CsPbIBr₂-based IPSCs. In the case of CsPbIBr₂ IPSCs, we introduce the low-temperature deposition of CsPbIBr₂ films, doping methods for the preparation of high-quality CsPbIBr₂ films and strategies for improving the performance of solar cells. Furthermore, the mechanism of crystallization/interface engineering for the preparation of high-quality CsPbIBr₂ films and efficient solar cells devices is emphasized. Finally, the development direction of further improving the PV performance and commercialization of mixed-halide IPSCs are summarized and prospected.

In recent years, inorganic perovskite solar cells (IPSCs), especially those based on CsPbI₂Br, have attracted considerable attention owing to their exceptional thermal stability and a well-balanced combination of light absorption and phase stability. This review provides an extensive overview of the latest progress in CsPbI₂Br PSCs, focusing on film deposition techniques, crystallization control, interface engineering, and charge transport layers (CTLs). High-efficiency CsPbI₂Br PSCs can be achieved through the optimization of these key aspects. Various strategies, such as solvent engineering, component/additive engineering, and interface optimization, have been explored to enhance the quality of CsPbI₂Br films and improve device performance. Despite significant progress, challenges remain, including the need for even higher quality films, a deeper understanding of interface energetics, and the exploration of novel CTLs. Additionally, long-term stability continues to be a critical concern. Future research should focus on refining film preparation methods, developing sophisticated interfacial layers, exploring compatible charge transport materials, and ensuring device durability through encapsulation and moisture-resistant materials.

All-inorganic CsPbI2Br inverted perovskite solar cells (PSCs) have drawn increasing attention because of their outstanding thermal stability and compatible process with tandem cells. However, relatively low open circuit voltage (Voc) has lagged their progress far behind theoretical limits. Herein, we introduce phenylmethylammonium iodide and 4-trifluoromethyl phenylmethylammonium iodide (CFPMAI) on the surface of a CsPbI2Br perovskite film and investigate their passivation effects. It is found that CFPMAI with a –CF3 substituent significantly decreases the trap density of the perovskite film by forming interactions with the under-coordinated Pb2+ ions and effectively suppresses the non-radiative recombination in the resulting PSC. In addition, CFPMAI surface passivation facilitates the optimization of energy-level alignment at the CsPbI2Br perovskite/[6,6]-phenyl C61 butyric acid methyl ester interface, resulting in improved charge extraction from the perovskite to the charge transport layer. Consequently, the optimized inverted CsPbI2Br device exhibits a markedly improved champion efficiency of 14.43% with a Voc of 1.12 V, a Jsc of 16.31 mA/cm2, and a fill factor of 79.02%, compared to the 10.92% (Voc of 0.95 V) efficiency of the control device. This study confirms the importance of substituent groups on surface passivation molecules for effective passivation of defects and optimization of energy levels, particularly for Voc improvement.