Abstract
The highly successful PBE functional and the modified Becke–Johnson exchange potential were used to calculate the structural, electronic, and optical properties of the vacancy-ordered double perovskites A2BX6 (A = Rb, Cs; B = Sn, Pd, Pt; X = Cl, Br, and I) using the density functional theory, a first principles approach. The convex hull approach was used to check the thermodynamic stability of the compounds. The calculated parameters (lattice constants, band gap, and bond lengths) are in tune with the available experimental and theoretical results. The compounds, Rb2PdBr6 and Cs2PtI6, exhibit band gaps within the optimal range of 0.9–1.6 eV, required for the single-junction photovoltaic applications. The photovoltaic efficiency of the studied materials was assessed using the spectroscopic-limited-maximum-efficiency (SLME) metric as well as the optical properties. The ideal band gap, high dielectric constants, and optimum light absorption of these perovskites make them suitable for high performance single and multi-junction perovskite solar cells.
Highlights
The highly successful PBE functional and the modified Becke–Johnson exchange potential were used to calculate the structural, electronic, and optical properties of the vacancy-ordered double perovskites A2BX6 (A = Rb, Cs; B = Sn, Pd, Pt; X = Cl, Br, and I) using the density functional theory, a first principles approach
To manipulate the vacancy-ordered double perovskites (DPs), we used wien2k37 code based on the density-functional theory (DFT)[38] by employing the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method with Perdew, Burke, and Ernzerhof functional (PBE)[39], modified Becke Johnson semi-local exchange p otential[40], and hybrid functional HSE0641
The atomic positions and geometric configuration of A2BX6 is illustrated in Fig. 1 which can be described as B-deficient ABX3 perovskites with [BX6] cluster
Summary
The power conversion efficiencies (PCEs) of these materials exceed 25% according to a recent report[4] Such a fast improvement is attributed to the unique photovoltaic properties of Pb halide perovskite absorbers, for example, tunable direct band gap, fair electron and hole effective mass, excellent optical absorption, high stability, benign defect tolerance, and long term photogenerated carrier diffusion lengths[5,6,7]. The C s2BI6 with B = Sn and Te have been reported capable of absorption of light in the visible to infrared (IR) region giving new hope for stable materials with a nature friendly operation[25,30,31] In this framework, Cs2SnI6 with cubic crystal structure containing Sn in its +4 oxidation state is regarded as a potential candidate for applications in perovskite solar cells (PSCs)[30].
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