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

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 concentration and control over crystallization dynamics. By
optimizing 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. 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 x 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.