Investigation of optoelectronic and photovoltaic characteristics of A2NaAlI6 (A = Rb, Cs)-based perovskite solar cells with different charge transport layers: DFT and SCAPS-1D simulation

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The recent advances in perovskite solar cells (PSCs) based on halide double perovskites (DPs) have stimulated considerable investigations to improve their overall functionality due to their outstanding optoelectronic features. Due to the toxicity of lead (Pb), the emergence of A 2 NaAlI 6 (A = Rb, Cs)-based PSCs is regarded as a good alternative to Pb-based PSCs. First, DFT simulations are conducted to investigate the potential of A 2 NaAlI 6 (A = Rb, Cs) as an absorber layer for PSCs. The investigations examined the structural, elastic, and optoelectronic properties. The elastic properties have demonstrated the ductility and directional anisotropy in examined halide DPs, validating their viability for flexible technologies. The band diagram and density of states confirmed the direct band gap of 1.78 eV and 1.7 eV, along with the significant contribution from electronic states of I-p, Na-s, and Al-p orbitals. The dielectric parameters and the absorption coefficient are substantial in the visible range of energy, confirming their immense value in solar energy technologies. This study also performed numerical simulation to examine the combination of the hole transport layers (HTLs) and electron transport layers (ETLs) with the A 2 NaAlI 6 absorber layer using the SCAPS-1D simulation. The designed combinations, ITO/ETL/A 2 NaAlI 6 /HTL with six combinations of CSTO, ZnS, and PEIE as the ETLs, MoO 3 and CuAlO 2 as the HTLs are optimized to demonstrate the photovoltaic features of simulated PSCs. The different combinations demonstrated varied efficiencies, among which the ITO/CSTO/A 2 NaAlI 6 /CuAlO 2 combinations have revealed the highest PCE at 25.12 % and 27.98 %, respectively. These observations indicate that A 2 NaAlI 6 (A = Rb, Cs) halide DPs are intriguing candidates for PSCs due to their superior stability and exceptional photovoltaic properties.