Optimized solar conversion achieved with double halide X2NaIrCl6 (X = Rb, Cs) perovskites for optoelectronic and photovoltaic applications

Considering the environmental concerns of lead Hazardousness and durability concerns in lead-based perovskite solar cells (PSCs), lead-free alternatives like X2NaIrCl6 (X = Rb, Cs) have gained significant attention. This investigation carries out an analysis of the structural and optoelectronic behaviour of X2NaIrCl6 (X = Rb, Cs) using DFT to assess its potential for absorber material for solar cells (SCs). Structural stability of X2NaIrCl6 (X = Rb, Cs) double perovskites was analysed using tolerance factors (τ1, μ, τ2), with dynamical stability ensured through phonon dispersion. Negative and binding energy (Eb) and formation energy (Ef) further validated their stability. Direct band gaps, determined utilizing the TB-mBJ (GGA-PBE) approach, the values were determined to be 2.02 eV (0.97 eV) for Rb2NaIrCl6 and 1.93 eV (0.92 eV) for Cs2NaIrCl6, placing them in the recommended range (0.8- 2.2 eV) for photoelectric conversion. X2NaIrCl6 (X = Rb, Cs) double perovskites exhibit remarkable potential for photovoltaic applications, driven by their high absorption coefficients (∼104) and favourable optical properties, including low energy loss and minimal reflectivity (<15 %). These attributes highlight their promise for high efficiency and low-cost materials for advanced optoelectronic and solar energy devices. SCAPS-1D software employed to identify the most efficient solar cell designs by incorporating various HTLs and ETLs. Among 40 tested configurations, the ITO/ZnO/Cs2NaIrCl6/Cu2O structure attains the maximum PCE of ∼20.39 %, while ITO/ZnO/Rb2NaIrCl6/Cu2O achieves ∼19.16 %. Additionally, the study examines the effects of varying ETL/absorber thicknesses and series and shunt resistances, and temperature on photovoltaic performance. A detailed investigation was conducted on the principal photovoltaic indicators, such as current-voltage characteristics, capacitance, quantum efficiency, Mott Schottky parameters, and the processes governing photocarrier generation and recombination. These findings highlight X2NaIrCl6 (X = Rb, Cs) as a suitable material for high-performance optoelectronic and photovoltaic real-world applications.