Exploring CaBCl3 (BK and Rb) chloroperovskites: DFT and SCAPS-1D insights into physical properties and solar cell performance

Abstract

This research utilizes first-principles density functional theory (FP-DFT) to explore the structural, electronic, mechanical, and optical properties of calcium-based chloroperovskites CaBCl₃ (BK and Rb) compounds. Additionally, the SCAPS-1D (Solar Cell Capacitance Simulator - 1 Dimension) method is employed to evaluate enhanced solar cell designs featuring CaBCl₃ as absorber layers. Both chloroperovskites compounds crystallize in the space group Pm3 m (221) and exhibit negative formation energies, confirming their thermodynamic stability. Mechanical analysis reveals their ductile nature, with reductions in shear modulus, Young's modulus, and bulk modulus observed as the cation shifts from K to Rb. The electronic properties were assessed through band structure and density of states (DOS) calculations, revealing direct band gaps of 1.987 eV for CaKCl₃ and 1.386 eV for CaRbCl₃, indicating their nature as narrow band gap semiconductors. DOS analysis shows that the conduction band is primarily influenced by the “Ca” element, while the valence band is mainly dominated by the “Cl” element. Charge density analysis further reveals the covalent nature of the Ca–K and Ca–Rb bonds through overlapping charge distributions, while the ionic character of the Ca–Cl bonds is evident from the absence of overlap. Optical analysis reveals CaKCl₃ and CaRbCl₃ as strong candidates for solar cell applications, owing to their favorable absorption coefficients, dielectric constants, reflectivity, and conductivity. The SCAPS-1D simulation determined the optimal PV parameters for CaBCl₃-based cells with a CdS buffer layer, taking into account different thicknesses, defect densities, and shallow acceptor densities. The Al/FTO/CdS/CaBCl₃/Au device demonstrated a power conversion efficiency (PCE) of 13.40 % for CaKCl₃ and 25.57 % for CaRbCl₃, with J_SC values of 11.39 mA/cm² and 31.34 mA/cm², fill factors of 87.37 % and 86.41 %, and V_OC of 1.346 V and 0.944 V, respectively. These findings provide valuable insights for advancing CaBCl₃-based inorganic PSCs.