From optoelectronics to scintillation applications: the versatility of lead-free halide double perovskites.

The increasing demand for sustainable, lead-free alternatives has catalyzed extensive research into halide double perovskites, an emerging class of materials distinguished by excellent structural versatility, tunable electronic properties, and enhanced environmental stability. The replacement of toxic lead with earth-abundant materials makes these compounds present a transformative pathway toward eco-friendly optoelectronic technologies. The current comprehensive review critically examines recent breakthroughs in the synthesis, characterization, and multifunctional applications of lead-free halide double perovskites highlighting superior light absorption, intrinsic defect tolerance, and compositional flexibility with their rapidly advancing roles in next-generation solar cells, photodetectors, and light-emitting devices. In addition, their high X-ray absorption coefficients and robust radioluminescence enable cutting-edge scintillation performance, with significant implications for medical imaging and radiation detection. In the current review, we signify a unified framework that balances sustainability, stability, and multifunctionality, with particular attention to emerging indoor photovoltaic technologies that exemplify tailored, application-driven material innovation. Despite considerable progress, critical challenges in environmental resilience and scalable synthesis remain to be addressed for widespread technological deployment. This review delineates the current landscape and future directions, positioning lead-free halide double perovskites at the forefront of sustainable materials research.