Vacancy-Ordered Double Perovskite Cs2TeI6 Thin Films for Optoelectronics

Vazquez-Fernandez, Isabel, Mariotti, Silvia, Hutter, Oliver, Birkett, Max, Veal, Tim D., Hobson, Theodore D. C, Phillips, Laurie J., Danos, Lefteris, Nayak, Pabitra K., Snaith, Henry J., Xie, Wei, Sherburne, Matthew P., Asta, Mark and Durose, Ken (2020) Vacancy-Ordered Double Perovskite Cs2TeI6 Thin Films for Optoelectronics. Chemistry of Materials, 32 (15). pp. 6676-6684. ISSN 0897-4756

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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 Cs2TeI6, which we have synthesized in thin film form for the first time. Exhaustive trials concluded that spin coating CsI and TeI4 using an anti-solvent method produced uniform films, confirmed as Cs2TeI6 by XRD with Rietveld analysis. They were stable up to 250°C, had an optical band gap of ~1.5 eV, absorption coefficients of ~6 x 104 cm-1, carrier lifetimes of ~2.6 ns (unpassivated 200 nm film), a work function of 4.95 eV and had 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.

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