Exploring Optoelectronic Behavior and Solar Cell Efficiency of Double Halide Perovskites M2KIrCl6 (M = Cs, Rb) through DFT and SCAPS-1D.

Due to environmental concerns with lead-based perovskite solar cells (PSCs), attention has shifted toward safer alternatives like M2KIrCl6 (M = Cs, Rb). This study extensively investigates the structural, electronic, and optical properties of M2KIrCl6 using density functional theory (DFT). The analysis evaluates the suitability of these compounds as absorber materials in solar cells, emphasizing their environmental friendliness, stability, and efficiency for light-harvesting applications. The structural stability of M2KIrCl6 double halide perovskites is analyzed using tolerance factors (τ1, μ, τ2), with dynamical stability confirmed via phonon dispersion analysis. Negative formation energy (Ef) and binding energy (Eb) further corroborate their thermodynamic stability. The direct band gaps calculated using both GGA-PBE and TB-mBJ methods were found to be 1.08 and 1.99 eV for Cs2KIrCl6, and 1.12 and 2.10 eV for Rb2KIrCl6, respectively. These bandgap values fall within the optimal range (0.8-2.2 eV) necessary for efficient photovoltaic conversion, showcasing their capability to serve as absorber layers in photovoltaic devices. Furthermore, these compounds demonstrate exceptional optical properties, including high absorption coefficients (∼104 cm-1), low energy losses, and minimal reflectivity (<15%), emphasizing their suitability for advanced optoelectronic and photovoltaic applications. To optimize solar cell performance, SCAPS-1D software was utilized to investigate various device configurations incorporating different Hole Transport Layers (HTLs) and Electron Transport Layers (ETLs). Among 32 configurations tested, the ITO/ZnO/Cs2KIrCl6/V2O5 structure reached a peak power conversion efficiency (PCE) of around 21.30%, while the ITO/ZnO/Rb2KIrCl6/V2O5 configuration exhibited around 18.30%. Additionally, the impact of ETL and absorber layer thicknesses, series and shunt resistances, and operating temperatures on device performance was thoroughly explored. Crucial photovoltaic metrics, including current density-voltage (J-V) curves, capacitance, quantum efficiency, Mott-Schottky characteristics, and photocarrier generation-recombination rates, were comprehensively analyzed, underscoring the remarkable potential of M2KIrCl6 as efficient and cost-effective materials for future solar energy and optoelectronic applications.