A copper-based 2D hybrid perovskite solar absorber as a potential eco-friendly alternative to lead halide perovskites

Abstract

Hybrid organic–inorganic perovskites (HOIPs) have attracted considerable attention for their scientific and technological potential in photovoltaics and optoelectronic devices. Recently, two-dimensional (2D) HOIPs have become established as useful active layers for photovoltaic applications, offering adjustable electronic levels, high charge carrier mobilities, and simplicity of thin-film device fabrication. In this work, we describe the preparation of a new Cu-based 2D hybrid perovskite, with the structural formula (C₆H₁₀N₂)[CuCl₄], of which crystallographic, spectroscopic, optical and magnetic properties have been studied and analyzed. The compound exhibits dominant ferromagnetic interactions. Fits of the χ(T) data to the 2D-ferromagnetic layer model yielded C = 0.456(2) emu-K mol-Oe⁻¹ and J = 5.5(1). Analysis of electromagnetic absorption and reflectance properties through the visible and near-infrared indicate an optical band gap of 1.24 eV (absorption) or 1.23 eV (reflection) and a direct, spin-forbidden electronic transition giving rise to a strong absorption band centered at 740 nm, which allows it to absorb a large portion of the solar spectrum. Although the absorption coefficient is lower than lead halide perovskites, it is greater than 1000 cm⁻¹ throughout the visible spectrum up to 1000 nm, giving the material potential as a solar absorber if relatively thick (∼5 μm) films are used. The nature of the electronic transition and frontier electronic states were studied by DFT and reveal valence and conduction bands arising from repeating CuCl₄ square planar structural units composed of hybridized Cl 3p_x,y orbitals and Cu 3d_x²−y² orbitals. The electronic structure and optical properties indicate that the material might be able to serve as a non-toxic alternative to lead-based HOIPs in some applications.