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 & DEG;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 & AP;2 & mu;m 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 x 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.