Presently, the Bi-based 3D A2(BB′)X6 double perovskites (DPs) show an excellent photovoltaic (PV) performance with ambient stability compared to Pb-based counterparts. The structural, electronic, and optical properties analyses of A2BiCuX6 (A=Cs, Rb, K, X=I, Br, Cl) DPs are performed by CASTEP software, and the Cs2BiCuI6 is found to be the best suitable absorber among all of them. The density of states calculation reveals that Cu-3d and X-p orbitals are the major contributors to valence band maxima (VBM), whereas Bi-6p orbitals are responsible for the contribution to conduction band minima (CBM). Using SCAPS-1D simulation tool, the impact of variation in thickness, defect density, mobility of charge carriers, series resistance (RS), shunt resistance (RSh), and device temperature on PV performance of the device has been analysed. The optimised all inorganic FTO/WS2/Cs2BiCuI6/MXene/Pt structured device has provided an excellent PV performance i.e., PCE of 31.25 %, FF of 82.71 %, VOC of 1.24 V, and JSC of 30.40 mA/cm2 using 2D structured ETL (WS2) and HTL (MXene). This analysis provides an advanced understanding of cheap, environmentally stable, easily obtainable Bi-Cu based DP counterparts, which can be used in the fabrication of PV cells practically.
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