Vacancy-Ordered Double Perovskite Cs<sub>2</sub>TeI<sub>6</sub> Thin Films for Optoelectronics
Isabel Vázquez-Fernández, Silvia Mariotti, Oliver S. Hutter, Max Birkett, T. D. Veal, Theodore D. C. Hobson, Laurie J. Phillips, Lefteris Danos, Pabitra K. Nayak, Henry J. Snaith, Wei Xie, Matthew Sherburne, Mark Asta, K. Durose
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.