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

Abstract

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 CsPb1–x Sr x Br3 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.

Enriched‐Bromine Surface State for Stable Sky‐Blue Spectrum Perovskite QLEDs With an EQE of 14.6%

“…[ 8–12 ] Recently, great breakthroughs have been achieved in the synthesis and performance of green‐ and red‐emitting PeQLEDs in recent years, [ 13–22 ] whereas the low performance of blue‐emitting PeQLEDs (wavelength range: 460–490 nm) impedes the development of commercial display applications for PeQLEDs. [ 23–27 ]…”

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performance of green-and red-emitting PeQLEDs in recent years, [13][14][15][16][17][18][19][20][21][22] whereas the low performance of blue-emitting PeQLEDs (wavelength range: 460-490 nm) impedes the development of commercial display applications for PeQLEDs. [23][24][25][26][27] The entire blue spectra are expected to be obtained by controlling the Br/Cl ratio in inorganic blue-emitting PeQDs (CsPb(Br x /Cl 1−x ) 3 ). [28] In contrast to defecttolerant CsPbI 3 and CsPbBr 3 QDs, deeper donor defects are easily created by halogen vacancies between the conduction band and valence band in CsPb(Br x /Cl 1−x ) 3 , which results in trapped excitons and non-radiative recombination, [29] limiting further improvement in the PLQY of the blue perovskite QDs.

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Environment‐Friendly Perovskite Light‐Emitting Diodes: Progress and Perspective

“…Efficient and spectra-stable PeLEDs made from this material exhibited an EL maximum at 495 nm, an EQE of 13.8% and a maximum brightness exceeding 6000 cd m −2 . [71] By the way, Shen et al demonstrated that the improved performance of Ca 2+ doped CsPbI 3 NC PeLEDs exhibiting about threefold maximum EQE of 7.8% and 2.2-fold T 50 of 85 min, which could attribute to the decreased defect densities of films and reduced hole injection barrier. Figure 2i shows their EL stable peaks at 683 nm with a full width at half-maximum (FWHM) of 35 nm under various driving voltages.…”

“…h) Schematic of Sr 2+ cations passivated by DFPPO, which offers strong binding and steric hindrance to block H 2 O. [ 71 ] Copyright 2022, ACS. i) EL spectra of Ca 2+ ‐doped CsPbI 3 NCs (0.40%) LEDs on various driving voltages and a photograph of the working device [inset in (i)].…”

“…Copyright 2018, Wiley-VCH. h) Schematic of Sr 2+ cations passivated by DFPPO, which offers strong binding and steric hindrance to block H 2 O [71]. Copyright 2022, ACS.…”