Cs₂AgBiBr₆ for Solar and Beyond: Technical Applications, Challenges, and Future Directions

The all-inorganic double perovskite Cs₂AgBiBr₆ has emerged as one of the most studied lead-free alternatives to conventional lead-halide perovskites, thanks to its outstanding chemical stability, pronounced defect tolerance, and negligible environmental toxicity. While its relatively wide indirect bandgap (approximately 1.95–2.2 eV) restricts the efficiency achievable in single-junction solar cells, this same characteristic proves advantageous for applications requiring high durability, extended carrier lifetimes, and low dark current — notably as the wide-gap component in tandem photovoltaic stacks, high-performance photodetectors, and ionizing radiation sensors. In recent years, researchers have also demonstrated the material's promise in low-dimensional forms such as colloidal nanosheets and nanocrystals, where quantum confinement effects enable modified electronic structure and enhanced optical response, paving the way toward potential uses in quantum photonics and confined charge-transport devices. Performance enhancement strategies documented in related studies include compositional tuning via halide or cation alloying, surface defect mitigation through various passivation approaches, nanoscale morphology control, and careful interface engineering. Important practical considerations — especially the relatively high cost of silver and challenges associated with large-scale synthesis — continue to influence the material's commercial prospects. The present review synthesizes the latest developments concerning pure Cs₂AgBiBr₆ and its derivative compositions, critically assesses its diverse technological roles spanning energy conversion, detection, and emerging quantum-related applications, and identifies promising research trajectories such as optimized tandem integration, scalable crystal growth methods, and machine-learning-assisted materials exploration. Drawing from relevant publications, this work offers a comprehensive, up-to-date outlook on the pathways through which Cs₂AgBiBr₆ may mature into a key material platform for next-generation sustainable optoelectronics and quantum technologies.