Magnetron Sputtering Deposition of High Quality Cs3Bi2I9 Perovskite Thin Films

Nontoxic all-inorganic perovskites are among the most promising materials for the realization of optoelectronic devices. Here, we present an innovative way to deposit lead-free, totally inorganic Cs3Bi2I9 perovskite from vapor phase. Taking use of a magnetron sputtering system equipped with a radiofrequency working mode power supply and a single target containing the correct ratio of CsI and BiI3 salts, it was possible to deposit a Cs3Bi2I9 perovskitic film on silicon and soda-lime glass. The target composition was optimized to obtain a stoichiometric deposition, and the best compromise was found with a mix enriched with 20% w/w of CsI. Secondly, the effect of post-deposition thermal treatments (150 ◦C and 300 ◦C) and of the deposition on a preheat substrate (150 ◦C) were evaluated by analyzing the chemical composition, the morphology, the crystal structure, and the optical properties. The thermal treatment at 150 ◦C improved the uniformity of the perovskite film; the one at 300 ◦C damaged the perovskite deposited. Depositing on a preheated substrate at 150 ◦C, the obtained film showed a higher crystallinity. An additional thermal treatment at 150 ◦C on the film deposed on the preheated substrate showed that the crystallinity remains high, and the morphology becomes more uniform.