Vacancy-Ordered Double Perovskite Cs₂TeI₆ Thin Films for Optoelectronics

Abstract

Alternatives\nto lead- and tin-based perovskites for photovoltaics\nand optoelectronics are sought that do not suffer from the disadvantages\nof toxicity and low device efficiency of present-day materials. Here\nwe report a study of the double perovskite Cs₂TeI₆, which we have synthesized in the thin film form for the first time.\nExhaustive trials concluded that spin coating CsI and TeI₄ using an antisolvent method produced uniform films, confirmed as\nCs₂TeI₆ by XRD with Rietveld analysis. They\nwere stable up to 250 °C and had an optical band gap of ∼1.5\neV, absorption coefficients of ∼6 × 10⁴ cm^–1, carrier lifetimes of ∼2.6 ns (unpassivated\n200 nm film), a work function of 4.95 eV, and a p-type surface conductivity.\nVibrational modes probed by Raman and FTIR spectroscopy showed resonances\nqualitatively consistent with DFT <i>Phonopy</i>-calculated\nspectra, offering another route for phase confirmation. It was concluded\nthat the material is a candidate for further study as a potential\noptoelectronic or photovoltaic material.