Vacancy-Ordered Double Perovskite Cs₂TeI₆ Thin Films for Optoelectronics

Abstract

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 Cs 2 TeI 6 , which we have synthesized in the thin film form for the first time. Exhaustive trials concluded that spin coating CsI and TeI 4 using an antisolvent method produced uniform films, confirmed as Cs 2 TeI 6 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 4 cm -1 , 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 Phonopy-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.