Stable and Efficient Green Perovskite Nanocrystal-Polysilazane Films for White LEDs Using an Electrospray Deposition Process

We successfully fabricated a stable, efficient, and easy-to-use CsPbBr₃ perovskite nanocrystal (PeNC)-embedded inorganic polymer film through an encapsulation step with a Si-N/Si-O-based polysilazane (PSZ) matrix via the electrospray (e-spray) deposition of a silazane (SZ) oligomer-decorated PeNC solution. To eliminate Pb²⁺ defect sites that are generated when the ligands are peeled from the PeNC surface, surface passivation of the Lewis acid/base adduct is possible by coupling the SZ oligomer (the donor of lone pairs) with Pb²⁺ sites (the acceptor of lone pairs). With the addition of the SZ oligomer, the photoluminescence quantum yield of photodegraded CsPbBr₃ PeNC was recovered and increased by 2.35-fold whereas the stability was improved significantly from an untreated CsPbBr₃ PeNC solution. During the e-spray deposition process, SZ-treated CsPbBr₃ PeNC solution droplets can react with atmospheric moisture to polymerize and form a Si-N/Si-O network encapsulant via a sol-gel reaction. The resultant CsPbBr₃-PSZ films showed improved stability levels under most environmental conditions, including air storage, blue light exposure, UV exposure, thermal exposure, and water immersion. The optimum CsPbBr₃-PSZ film-covered blue light-emitting diode (LED) showed good performance capabilities, with a luminous efficacy (LE) of 85.9 lm/W and color-by-blue conversion efficiency (CE) of 60.1%. Furthermore, this easy-to-use CsPbBr₃-PSZ film can be employed to realize a remote-type white-by-blue LED by combining it with red emissive K₂SiF₆:Mn⁴⁺/silicone film. The LE and CE rates of the white LED were 71.0 lm/W and 50.8%, respectively, at a correlated color temperature of 9334 K, with only an 8% drop in the LE for long-term operation of 100 h. This result indicates that e-spray deposition is a simple fabrication process by which to create stable and efficient PeNC films from an unstable PeNC solution using a rapid sol-gel reaction between droplets and moisture from the air.