Advances and prospects of lead-free metal halide perovskites for solar hydrogen fuel generation

Abstract

Photocatalytic hydrogen production powered by solar energy is a foundational technology for a sustainable hydrogen economy. Lead-free metal halide perovskites (MHPs) are at the forefront of this field, lauded for their superb optoelectronic properties and environmental compatibility. However, realizing their full potential requires overcoming the significant stability and performance challenges that have hindered widespread adoption. This article provides a critical and updated assessment of the remarkable progress in lead-free MHP development, with a specific focus on compositions centered around tin (Sn), bismuth (Bi), antimony (Sb), and copper (Cu), as well as advanced double perovskite structures. We explore the core principles of material design, from crystal and electronic band structure engineering to innovative strategies for enhancing stability in aqueous environments, such as heterostructuring, dimensionality control, and surface passivation. The analysis includes a review of performance benchmarks, including hydrogen evolution rates now exceeding 1700 μmol g⁻¹ h⁻¹ (among the highest reported for tin-based systems and competitive with some lead-based analogues), and the optimization techniques that enable such achievements. Despite these advances, formidable challenges remain in achieving long-term operational stability and closing the efficiency gap with both lead-based counterparts and the targets for economic viability, which project a need for green hydrogen costs below $2/kg. We conclude by outlining the key future research frontiers essential for propelling these eco-friendly photocatalysts toward large-scale solar fuel generation. These frontiers include the urgent need for standardized testing protocols, a deeper mechanistic understanding through operando studies, and the integration of machine learning for accelerated materials discovery and inverse design, all of which are imperative for translating laboratory breakthroughs into practical, impactful technologies.