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.

Halide perovskite solar cells (HPSCs) are promising photovoltaic materials due to their excellent optoelectronic properties, low cost, and high efficiency. Here, we demonstrate atmospheric solution processing and stability of cesium tin-lead triiodide (CsSnPbI₃) thin films for solar cell applications. The effect of additives, such as pyrazine and guanidinium thiocyanate (GuaSCN), on bandgap, film morphology, structure, and stability is investigated. Our results indicate the formation of a wide bandgap (>2 eV) structure with a mixed phase of tin oxide (SnO₂) and Cs(Sn, Pb)I₃. The addition of pyrazine decreases the intensity of SnO₂ peaks, but the bandgap does not change much. With the addition of GuaSCN, the bandgap of the films reduces to 1.5 eV, and a dendritic structure of Cs(Sn, Pb)I₃ is observed. GuaSCN addition also reduces the oxygen content in the films. To enable uniform film crystallization, cesium chloride (CsCl) and dimethyl sulfoxide (DMSO) additives are used in the precursor. Both CsCl and DMSO suppress dendrite formation with the latter resulting in uniform polycrystalline films with a bandgap of 1.5 eV. Heat and light soaking (HLS) stability tests at 65 °C and 1 sun for 100 h show all film types are stable with temperature but result in phase segregation with light exposure.