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

Abstract

We investigated the structural stability, density of states (DOS), optical and electronic properties of Cs 2 TeX 6 (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 Cs 2 TeX 6 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 (≈10 5 cm –1 ) of the Cs 2 TeI 6 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 Cs 2 TeI 6 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: TiO 2 and WS 2 ). The optimum power conversion efficiency (PCE) of the FTO/n-WS 2 /Cs 2 TeI 6 /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/cm 2, and 80.53%, respectively. In addition, the photovoltaic response of the Cs 2 TeX 6 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.

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