Ultrapure and efficient electroluminescence in alkali metal doped inorganic perovskite quantum wires arrays

Abstract

Alkali metal doping has been widely utilized to regulate metal halide perovskites and improve their luminescence performance. However, due to the discordant tolerance factor caused by the smaller size of potassium and rubidium ions, it is still debatable whether they can be incorporated in the cesium perovskite crystal lattice. Here we provide unambiguous evidence for the formation of Rb⁺ and K⁺ substitutionally doped stable perovskite cubic crystal structure in the form of quantum wires embedded in nanoporous alumina template. The suppressed inner defects and enhanced exciton binding energy lead to a reduced non-radiative recombination in the co-doped perovskite quantum wires. The perovskite light-emitting diodes with a maximum external quantum efficiency of 17.5%, 21.2%, 24.9% and 30.1% and a maximum luminance of 1638 cd m^-2, 3365 cd m^-2, 13,483 cd m^-2 and 31,706 cd m^-2 for electroluminescence peak of 476 nm (primary-blue), 483 nm (sky-blue), 490 nm (sky-blue) and 512 nm (green) are fabricated respectively. Surprisingly, all devices emit high-color purity light with narrow linewidth of ≤16 nm.

Fig. 1. Substitution of Cs with Rb and K at A-site in alkali metals doped PeQW arrays.

a Schematic illustration of the fabrication of alkali metals doped PeQW arrays and substitution of Cs with Rb and K at A-site in PeQW. Inset, cross-sectional TEM image of PeQW arrays. Scale bar, 200 nm. b Atomically resolved low-dose HRTEM image of single pristine CsPbBr₃ QW with atomic structure model projected along <100> direction. Scale bar, 2 nm. Inset, fast Fourier transform diffractograms showing the cubic lattice structure. Scale bar, 2 nm⁻¹. c, d Zoom-in low-dose HRTEM image of perovskite lattice in the edge and middle of pristine CsPbBr₃ QW. Scale bar, 1 nm. e Rb 3 d and K 2p XPS core-level spectra of Rb⁺, K⁺: CsPbBr₃ QWs. f XRD pattern of pristine CsPbBr₃ QW, Rb⁺: CsPbBr₃ QWs and Rb+, K⁺: CsPbBr₃ QWs. g GIWAXS pattern and in-plane intensity profiles extracted from the GIWAXS of pristine CsPbBr₃ QW, Rb⁺: CsPbBr₃ QWs and Rb⁺, K⁺: CsPbBr₃ QWs. h Atomically resolved low-dose HRTEM image of single pristine CsPbBr₃ QW with atomic structure model projected along <110> direction. Scale bar, 2 nm. Inset, fast Fourier transform diffractograms showing the cubic lattice structure. Scale bar, 5 nm⁻¹. i, j Zoom-in low-dose HRTEM image of perovskite lattice in the edge and middle of Rb⁺, K⁺: CsPbBr₃ QWs. Scale bar, 1 nm.

Fig. 2. DFT calculation of formation energy for the substitution of Cs with Rb and K at A-site.

a Schematic drawing of Rb or K replacing Cs at A-site in the model without Al₂O₃. b Formation energy of Rb or K replacing Cs at A-site. c Schematic drawing of Rb or K replacing Cs at A-site in the model with Al₂O₃. d Formation energy of Rb or K replacing Cs at A-site in the bulk of CsPbBr₃. e Formation energy of Rb or K replacing Cs at A-site at the interface of CsPbBr₃ and Al₂O₃.

Fig. 3. Properties of alkali metals doped PeQW arrays.

a XRD patterns, b Normalized photoluminescence spectra (${\lambda }_{ex}=350nm$), c TRPL decay curves and d PLQYs (${\lambda }_{ex}=365nm$) measured at corresponding photoluminescence peak of as-synthesized alkali metals doped PeQWs. e Environmental photoluminescence stability under ambient condition for alkali metal doped PeQWs.

Fig. 4. Characteristics of PeLEDs based on alkali metals doped PeQW arrays.

a Schematic of alkali metals doped PeQWs-based LED architecture. b Cross-sectional SEM image of a device. The thickness of each layer, which can be confirmed by SEM, are shown below: Al electrode/Al₂O₃ hole blocking layer (~5 nm)/PeQWs emission layer (90 nm)/TAPC hole transporting layer (20 nm)/HAT-CN hole injecting layer (20 nm)/ITO transparent electrode (90 nm). Scale bar, 200 nm. c Energy band diagram of each layer in PeLEDs. d Normalized electroluminescence spectra of blue and green PeLEDs. e The corresponding CIE coordinates of blue and green PeLEDs. f Current density (J)-voltage (V)-luminance (L) curves. g, h External quantum efficiency (EQE)-luminance (L) curves. i The EQEs distribution collected from 72 devices. The average peak EQEs are 15.8%, 18.2%, 20.2% and 26.2% with relative standard deviations of 7.7%, 7.3%, 11.1% and 7.3%, respectively.