Vacancy-Ordered Double Perovskite CsTeI Thin Films for Optoelectronics.

Alternatives to lead- and tin-based perovskites for photovoltaics and optoelectronics are sought that do not suffer from the disadvantages of toxicity and low device efficiency of present-day materials. Here we report a study of the double perovskite CsTeI, which we have synthesized in the thin film form for the first time. Exhaustive trials concluded that spin coating CsI and TeI using an antisolvent method produced uniform films, confirmed as CsTeI by XRD with Rietveld analysis. They were stable up to 250 °C and had an optical band gap of ∼1.5 eV, absorption coefficients of ∼6 × 10 cm, carrier lifetimes of ∼2.6 ns (unpassivated 200 nm film), a work function of 4.95 eV, and a p-type surface conductivity. Vibrational modes probed by Raman and FTIR spectroscopy showed resonances qualitatively consistent with DFT -calculated spectra, offering another route for phase confirmation. It was concluded that the material is a candidate for further study as a potential optoelectronic or photovoltaic material.