Bandgap tuning through the substitution of alkali metal cations in A2AlCuF6 (A = K, Rb, and Cs) for optoelectronic and renewable energy applications

Abstract

Perovskite halides are an attractive choice for renewable energy harvesting as these materials offer high flexibility and bandgap tunability. This study interrogates the first principles analysis of A₂AlCuF₆ (A = K, Rb, and Cs) done via DFT simulations. The FP-LAPW approach is employed to assess the physical attributes of A₂AlCuF₆ (A = K, Rb, and Cs). The structural attributes reveal a significant increase in lattice constant and ground state energy as the A-site cation is replaced by K → Rb → Cs, while the reported bulk modulus reveals a declining trend. The negative formation energies and the tolerance factor values confirm thermodynamic and structural stability. The electronic bandgap reveals an increasing trend as the A-site is replaced by K → Rb → Cs, revealing indirect bandgaps of 2.80 eV, 2.78 eV and 3.10 eV for K₂AlCuF₆, Rb₂AlCuF₆ and Cs₂AlCuF₆, respectively. The optical analysis suggests that among the studied halides, Cs₂AlCuF₆ reports high absorption and minimum energy loss in the UV region, making it an ideal candidate for UV shields and UV photodetectors. The thermoelectric attributes reveal high ZT values at elevated temperatures, revealing that K₂AlCuF₆, Rb₂AlCuF₆ and Cs₂AlCuF₆ are suitable contenders for the production of energy from waste heat.