Wide-Bandgap Perovskite Quantum Dots in Perovskite Matrix for Sky-Blue Light-Emitting Diodes

The epitaxial growth of a perovskite matrix on quantum dots (QDs) has enabled the emergence of efficient red light-emitting diodes (LEDs) because it unites efficient charge transport with strong surface passivation. However, the synthesis of wide-band gap (E_g) QD-in-matrix heterostructures has so far remained elusive in the case of sky-blue LEDs. Here, we developed CsPbBr₃ QD-in-perovskite matrix solids that enable high luminescent efficiency and spectral stability with an optical E_g of over 2.6 eV. We screened alloy candidates that modulate the perovskite E_g and allow heteroepitaxy, seeking to implement lattice-matched type-I band alignment. Specifically, we introduced a CsPb_1-SrBr₃ matrix, in which alloying with Sr²⁺ increased the E_g of the perovskite and minimized lattice mismatch. We then developed an approach to passivation that would overcome the hygroscopic nature of Sr²⁺. We found that bis(4-fluorophenyl)phenylphosphine oxide strongly coordinates with Sr²⁺ and provides steric hindrance to block H₂O, a finding obtained by combining molecular dynamics simulations with experimental results. The resulting QD-in-matrix solids exhibit enhanced air- and photo-stability with efficient charge transport from the matrix to the QDs. LEDs made from this material exhibit an external quantum efficiency of 13.8% and a brightness exceeding 6000 cd m^-2.