Two-step spin-coating of vacancy-ordered double perovskites enables growth of thin films for electronic devices

Abstract

Vacancy-ordered double perovskites (VODPs), such as Cs₂TeX₆ (X = Cl, Br, I), are lead-free alternatives to conventional metal-halide perovskites (MHPs). One limitation of VODPs is the lack of processes to form thin films relevant for physical characterization and electronic devices. A two-step spin-coating method was developed for synthesizing high-quality films of Cs₂TeBr₆. Independently depositing CsBr and TeBr₄ enables high precursor concentrations and control over crystallization kinetics. By optimizing the spin-coating parameters, conversion of precursors to phase pure films was observed using structural and surface characterization methods. The growth of mixed-halide systems was investigated using alternative salts including CsCl and CsI. The formation of halide alloys was found to depend on the existence of routes to byproducts. Lastly, single carrier diodes of Cs₂TeBr₆ were designed following valence band characterization with photoelectron spectroscopy. Temperature-dependent space-charge-limited current measurements revealed that transport occurs by hopping and the hole mobility is 3.2 × 10⁻⁵ cm² V⁻¹ s⁻¹ near room temperature. The insights from the 2-step procedure provide a pathway towards making semiconducting devices from VODPs.