SnF₂‐Doped Cs₂SnI₆ Ordered Vacancy Double Perovskite for Photovoltaic Applications

Air‐stable p‐type SnF₂:Cs₂SnI₆ with a bandgap of 1.6 eV has been demonstrated as a promising material for Pb‐free halide perovskite solar cells. Crystalline Cs₂SnI₆ phase is obtained with CsI, SnI₂, and SnF₂ salts in gamma‐butyrolactone solvent, but not with dimethyl sulfoxide and N,N‐dimethylformamide solvents. Cs₂SnI₆ is found to be stable for at least 1000 h at 100 °C when dark annealed in nitrogen atmosphere. In this study, Cs₂SnI₆ has been used in a superstrate n–i–p planar device structure enabled by a spin‐coated absorber thickness of ≈2 μm on a chemical bath deposited Zn(O,S) electron transport layer. The best device power conversion efficiency reported here is 5.18% with V_OC of 0.81 V, 9.28 mA cm⁻² J_SC, and 68% fill factor. The dark saturation current and diode ideality factor are estimated as 1.5 × 10⁻³ mA cm⁻² and 2.18, respectively. The devices exhibit a high V_OC deficit and low short‐circuit current density due to high bulk and interface recombination. Device efficiency can be expected to increase with improvement in material and interface quality, charge transport, and device engineering.