Inorganic Cs₂TeX₆ (X = Cl, Br, I) Lead-Free Vacancy-Ordered Double-Perovskite Absorber-Based Single-Junction Solar Cells with a Higher Efficiency of ∼24%: Theoretical Insights

We investigated the structural stability, density of states (DOS), optical and electronic properties of Cs₂TeX₆ (X = Cl, Br, I) vacancy-ordered double perovskites (VoDPs) using first-principles calculations. These VoDPs exhibit good structural stability based on tolerance factors, the Brown equation, and the formation energy. The calculated indirect bandgaps of Cs₂TeX₆ systems are also in agreement with the reported experimental values. We observed that the eigenband corresponding to the minima of the conduction band (CB) seems to be detached from the CB upon the consideration of spin–orbit coupling (SOC), and more band bending occurs at the “L” point. Overall, the high absorption coefficient (≈10⁵ cm^–1) of the Cs₂TeI₆ system, together with other optoelectronic properties in the visible spectrum range with moderate reflectance (∼33%), makes it a suitable photovoltaic (PV) absorber material. Furthermore, the PV performance of Cs₂TeI₆ material-based single-junction solar cell (SC) is investigated in the planar regular device configuration (n–i–p structure) for two different electron transport materials (ETMs: TiO₂ and WS₂). The optimum power conversion efficiency (PCE) of the FTO/n-WS₂/Cs₂TeI₆/p-NiO SC configuration is found to be ∼23.74% together with open-circuit voltage (V_oc), current density (J_sc), and fill factor (FF) values of ∼1.094 V, 26.955 mA/cm², and 80.53%, respectively. In addition, the photovoltaic response of the Cs₂TeX₆ absorber-based SC is also substantiated using the spectroscopic limited maximum efficiency (SLME) approach. Thus, the present work will play an important role in the realization of efficient lead-free VoDP-based single-junction SCs and other optoelectronic applications.