Stable Perovskite Core-shell Nanocrystals as Down-Converting Phosphors for Solid State Lighting

Colloidal perovskite quantum dots (QDs) or nanocrystals (NCs) with structure of CsPbX3 (X = Cl, Br, I) are promising materials as down-converting phosphors due to their high quantum yield up to >90%, extremely narrow emission band ~15-30 nm, and tunable emission wavelengths of ~410−700 nm via size or composition control. Compared to other QD materials, the optical and electronic properties of perovskite NCs are much more tolerant to defects so highly efficient light- emitting NCs can be easily prepared without carefully removing surface defects. Also, precision size control is not required for obtaining perovskite NCs with narrow emission <30 nm and can greatly enhance the reproducibility and yield rate during mass production. The challenges in using perovskite NCs as LED phosphors are their hygroscopic nature and self-absorption as observed from other QDs. We propose to synthesize core-shell structure perovskite NCs to improve their stability by over-coating a SiO2 layer, followed by further sol-gel processing into stable micro- sized glass beads. To increase Stokes shift and avoid self-absorption, core/graded-shell/shell structure such as CsSnBr3/CsSn1-xPbxBr3/CsPbBr3 NCs will be prepared, similar to a concept we demonstrated before in CdSe/Cd1-xZnxSe1-ySy/ZnS structure with significantly separated absorption and emission bands. These NC materials will be integrated into films and used as remote or on-chip downconverters for high efficiency, high CRI and warm white LED. To achieve this goal, PhosphorTech Corporation (PTC) has teamed with Georgia Tech (GT) to develop this unique perovskite system for pcLEDs that offers the promise of high luminous efficacy over a broad temperature and optical flux range.