Cu-Induced Phase Transitions and Energy Bandgap Tuning in 2D Ruddlesden-Popper Perovskites

Ruddlesden-Popper perovskites exhibit exceptional potential for optoelectronic applications; however, the presence of toxic lead poses significant challenges to their further development. In this study, we have successfully developed transition-metal-substituted 2D perovskite (BA)₂Pb_xCu_1-xCl₄ as lead-reduced alternatives, addressing concerns related to lead toxicity and material stability. Structural characterization using powder X-ray diffraction confirms the incorporation of Cu²⁺ ions into the perovskite lattice. This incorporation enables optical energy bandgap tuning from 3.55 to 2.27 eV, rendering both Cu-Pb mixed and pure Cu perovskites highly suitable for optoelectronic applications. Additionally, temperature-dependent X-ray diffraction and photoluminescence spectroscopy reveal key reversible structural phase transitions around 200 K in Cu-Pb mixed perovskites, attributed to octahedral tilting and Jahn-Teller distortions. These results highlight the potential of Cu-Pb mixed perovskites as environmentally friendly materials, suitable for next-generation optoelectronic devices as well as applications in thermochromic and ferroelectric technologies.