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

We successfully fabricated stable, efficient, and easy-to-use CPbBr 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 Pb defect sites which were generated by peeling off the ligands from the PeNC surface, surface passivation of the Lewis acid/base adduct could be achieved by coupling the SZ oligomer (the donor of lone pairs) with Pb sites (the acceptor of lone pairs). With the addition of the SZ oligomer, the PLQY of photo-degraded CsPbBr PeNC was recovered and increased by 2.35-fold while the stability was improved significantly from an untreated CsPbBr PeNC solution. During the E-spray deposition process, SZ-treated CsPbBr PeNC solution droplets can react with atmospheric moisture to polymerize and form the Si-N/Si-O network encapsulant via a sol-gel reaction. The resultant CsPbBr-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 CsPbBr-PSZ film-covered blue 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 CsPbBr-PSZ film can be employed to realize a remote-type white-by-blue LED through combining it with red emissive KSiF: Mn (KSF)/silicone film. The LE and CE 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 hours. This result indicates that the E-spray deposition process 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.