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 (${\tau }_1$, μ, ${\tau }_2$), with dynamical stability ensured through phonon dispersion. Negative and binding energy ($E_b$) and formation energy ($E_f$) 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.