Inorganic lead-free double perovskites for eco-friendly energy conversion technology

Fuel and energy sources are crucial for the advancement of humanity and switching to renewable energy sources from non-renewable sources has become an urgent necessity. Among the various known sustainable resources such as wind, small-hydro and geothermal solar energy has emerged as the most promising energy resource, with its efficiency largely determined by the choice of materials. In recent years, lead-free double perovskite (DPs) materials, A₂BB′X₆ where ‘A’ is alkali metal, ‘B’ and ‘B′’ are transition or post-transition metals, and ‘X’ are oxides or halides, have gained significant attention as these perovskites demonstrate good environmental stability, eco-friendly nature, and are non-toxic nature and potential for diverse applications in energy storage, optoelectronic, and thermoelectric. In this review, we have systematically explored the structural, optoelectronic and thermoelectric properties of oxide and halide DPs with particular emphasis on their potential in photovoltaic applications. We have examined the role of these DPs in improving the stability of perovskite solar cells (PSCs), the design of single-junction structures and the cohesive strategies to broaden solar spectrum utilization. We have also highlighted the recent progress in computational and experimental approaches, and provides future directions for designing high-performance lead-free double perovskites. This review also provide a critical analysis on the challenges and limitations of perovskite materials, including bandgap tunability, stability–efficiency trade-offs, and intrinsic material constraints. The article identifies emerging strategies and knowledge gaps that could accelerate the advancement of lead-free double perovskites for eco-friendly energy conversion technologies.