Comprehensive exploration of a two-dimensional Cu(II)-based perovskite: a high UV–Vis–NIR absorber

A new two-dimensional lead-free halide perovskite with the structural formula (C₄H₁₄N₂)[CuCl₄] was synthesized and extensively characterized. The compound was analyzed using single-crystal X-ray diffraction, vibrational spectroscopy, UV−Vis−NIR diffuse reflectance spectroscopy, Ab initio simulations with VASP, and thermal analysis. X-ray diffraction studies revealed that the hybrid material crystallizes in the monoclinic phase with the centrosymmetric space group P2₁/c. The vibrational spectra were analyzed to identify the principal vibration modes and their assignments. Optical analysis using the Kubelka–Munk equation determined a direct allowed band gap transition with an energy level of 2.47 eV, indicating that this hybrid material is a semiconductor, consistent with theoretical calculations. Density functional theory (DFT) calculations showed that the valence band is primarily composed of Cl p-states, while the conduction band is mainly composed of Cu d-states. Thermal analysis (TGA-DTA) demonstrated that the compound is stable up to 200 °C, with gradual decomposition occurring up to 576 °C, releasing various compounds, including CH₄, NO₂, CO₂, and Cl₂, and ultimately forming copper oxide (CuO) as the final product.