Theoretical investigations of electronic and optical properties of double perovskite Cs2TlBX6 (B= Bi, In; X= Cl, Br, I) for photovoltaic application
Abstract
Lead-free double perovskites are gaining attention for photovoltaic (PV) applications due to their long carrier lifetimes, tunable bandgaps, and low toxicity. Using first-principles calculations, we studied the structural, electronic and optical properties of Cs2TlBX6 (B= Bi, In; X= Cl, Br, I). The cubic phase (space group Fm3m) was analyzed within the projector-augmented wave (PAW) method. Our calculations predict direct bandgaps of 1.9-1.2 eV for Cs2TlBiX6 and indirect bandgaps of 2.4--0.8 eV for Cs2TlInX6. Notably, the bandgap energy decreases with anion substitution from Cl to I, making these materials highly active in the near-infrared to visible light range. We reveal that Cs2TlBiX6 exhibits the highest optical absorption, with a peak value of 5×105 cm-1 at an incident photon energy of 3 eV. Additionally, we evaluated the transport properties using the Boltzmann transport equations. The results indicate that Cs2TlBiX6 exhibit high electrical conductivity, reaching 8×106 S/m, and high electron mobility of 120 cm2/V.s. PV performance analysis further reveals promising power conversion efficiencies (PCE) of up to 42\%, with Cs2TlBiX6 showing significantly higher PCE than Cs2TlInX6. These reports highlight the potential of Cs2TlBiX6 for advanced photovoltaic devices.
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