Lead to Bismuth in Halide Perovskites: Effects on Structural and Optical Characteristics

Abstract Organic-inorganic halide perovskites have emerged as promising materials for optoelectronic applications; however, the presence of toxic lead poses significant environmental and health concerns, motivating the search for lead-free alternatives. In this study, we investigate the effect of substituting lead with bismuth on the structural, morphological, and optical characteristics of halide perovskite thin films. X-ray diffraction analysis reveals that MAPbBr 3 crystallizes in a highly ordered three-dimensional perovskite structure with strong preferential orientation, whereas MA 3 Bi 2 Br 9 forms a low-dimensional, perovskite derived structure consisting of isolated Bi 2 Br 9 3− units. Morphological studies using scanning electron microscopy show compact, uniform, and densely packed grains in MAPbBr 3 films, while MA 3 Bi 2 Br 9 exhibits discontinuous morphology with irregular grains and increased voids, reflecting altered crystallization behavior due to reduced structural dimensionality. Optical measurements indicate strong visible-light absorption and a direct band gap of ~ 2.28 eV for MAPbBr 3 , whereas MA 3 Bi 2 Br 9 displays weaker absorption with a blue-shifted onset and an indirect band gap of ~ 2.67 eV. These findings highlight the fundamental trade-off between optoelectronic performance and environmental sustainability upon lead substitution. The study provides critical insights into structure–property relationships in bismuth-based perovskites and underscores their potential and limitations for developing eco-friendly optoelectronic devices.