Advances in All-Inorganic Perovskite Nanocrystal-Based White Light Emitting Devices

Abstract

Metal halide perovskites (MHPs) are exceptional semiconductors best known for their intriguing properties, such as high absorption coefficients, tunable bandgaps, excellent charge transport, and high luminescence yields. Among various MHPs, all-inorganic perovskites exhibit benefits over hybrid compositions. Notably, critical properties, including chemical and structural stability, could be improved by employing organic-cation-free MHPs in optoelectronic devices such as solar cells and light-emitting devices (LEDs). Due to their enticing features, including spectral tunability over the entire visible spectrum with high color purity, all-inorganic perovskites have become a focus of intense research for LEDs. This Review explores and discusses the application of all-inorganic CsPbX₃ nanocrystals (NCs) in developing blue and white LEDs. We discuss the challenges perovskite-based LEDs (PLEDs) face and the potential strategies adopted to establish state-of-the-art synthetic routes to obtain rational control over dimensions and shape symmetry without compromising the optoelectronic properties. Finally, we emphasize the significance of matching the driving currents of different LED chips and balancing the aging and temperature of individual chips to realize efficient, uniform, and stable white electroluminescence.

Figure 1

(a) Perovskite NC entities in the stock solution (left) and the 3D arrangement of perovskite structures (right). Pink balls represent the monovalent cation Cs⁺, orange balls indicate the face-centered halide ions X^–, and blue balls at the center of octahedra are divalent Pb²⁺ cations. (b) STEM image of monodisperse CsPbBr₃ QDs. Adapted with permission from ref (6c). Copyright 2022 Science. (c) TEM image of anisotropic CsPbBr₃ nanoplatelets. Adapted from ref (8a). Copyright 2020 American Chemical Society. (d) HRTEM image of flat flying 2D NRs. Adapted with permission from ref (8b). Copyright 2022 American Chemical Society. (e) Schematic illustration of OLPA-based CsPbBr₃ nanocrystals passivated by hydrogen phosphonates, phosphonic acid anhydrides, and phosphonate species. Adapted with permission from ref (9d). Copyright 2020 American Chemical Society. (f) Perovskite deposition on ETL and HTL deposition on top of the perovskite layer. (g) Device operation of a fully fabricated LED upon applying bias. (h) Electron–hole recombination process inside the perovskite layer.

Figure 2

(a) Device structure of a typical perovskite LED. (b) Energy level diagram of a perovskite LED. (c) Schematic illustration of potassium passivation in CsPb(Br/Cl)₃ NCs. Adapted with permission from ref (12a). Copyright 2020 Wiley. (d) Curve of the luminance as a function of the driving voltage. (e) Curve of the external quantum efficiency of the device as a function of current density for Ni²⁺ ion-doped CsPbCl_xBr_3–x quantum dots. d, e Adapted with permission from ref (12b). Copyright 2020 American Chemical Society.

Figure 3

(a) Variation of the PL lifetime of untreated and CdCl₂-treated CsPbCl₃ nanocrystals with the temperature (268–328 K). Adapted with permission from ref (12c). Copyright 2019 American Chemical Society. (b) Schematic of the bipolar shell resurfacing of perovskite QDs comprised of an inner anion shell and an outer shell made up of cations and solvent molecules (top). EQE of exchanged blue LEDs with the variation in the current density based on CsPbBr₃ QDs (bottom). Adapted with permission from ref (14b). Copyright 2020 Springer Nature. (c) EQE–J curves of the LED devices based on quantum-confined CsPbBr₃ nanoplatelet-based 4.5 and 7 nm thick emitter layers. The inset shows the CIE color coordinate and photograph of a LED device (based on a 4.5 nm thick emitter layer) with an emitting size of 4 mm² at an applied current density of 52 mA cm^–2. Adapted with permission from ref (16a). Copyright 2022 American Chemical Society. (d) Evolution of the EQE with the driving current density for CsPbBr₃ QDs. Adapted with permission from ref (18a). Copyright 2022 Springer Nature.

Figure 4

(a) Schematic energy band structure of a CsPbBr_xCl_3–x nanocrystal-based blue LED, (b) EL spectra, and (c) CIE coordinates with different weight ratios for the CsPbBr_xCl_3–x nanocrystal and MEH:PPV blend-based white LED (the inset shows the white LED photo). Adapted with permission from ref (18c). Copyright 2017 Wiley. (d) Schematic diagram of a white LED based on CsPbBr₃ and CSAN:Eu² composite films stacked on a blue LED. (e) Evolution of CIE coordinates of a WLED under various operation currents. (f) Color coordinates of a WLED operated at 20 mA after 30 min. The inset depicts the fully operated WLED. Adapted with permission from ref (19a). Copyright 2018 Elsevier.

Figure 5

(a) PL stability in air and (b) water resistance of pristine CsPbBr₃ NCs and PMAO-coated CsPbBr₃ NCs. The inset in (a) shows the photograph of a working LED. Adapted with permission from ref (19c). Copyright 2019 American Chemical Society. (c) EL spectra under continuous work of the white LED based on a GaN-based blue chip, green-emitting CsPbBr₃ QDs/PDMS, and a red-emitting CsPbBrI₂ QDs/PDMS layer operated continuously for 8 h (inset shows a digital photograph of the working white LED). Adapted with permission from ref (21). Copyright 2019 Springer. (d) Corresponding color coordinates of the WLED at different driving currents. The inset shows the working image of the WLED at 5 mA. Adapted with permission from ref (23a). Copyright 2021 Elsevier.