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 (E_f) and binding energy (E_b) 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.