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. 2019 Nov 8;4(11):2703-2711.
doi: 10.1021/acsenergylett.9b01915. Epub 2019 Oct 11.

Direct Synthesis of Quaternary Alkylammonium-Capped Perovskite Nanocrystals for Efficient Blue and Green Light-Emitting Diodes

Yevhen Shynkarenko  1   2 , Maryna I Bodnarchuk  1   2 , Caterina Bernasconi  1   2 , Yuliia Berezovska  1   2 , Vladyslav Verteletskyi  1   2 , Stefan T Ochsenbein  1   2 , Maksym V Kovalenko  1   2
Affiliations

Direct Synthesis of Quaternary Alkylammonium-Capped Perovskite Nanocrystals for Efficient Blue and Green Light-Emitting Diodes

Yevhen Shynkarenko et al. ACS Energy Lett. .

Abstract

Cesium lead halide nanocrystals (CsPbX3 NCs) are new inorganic light sources covering the entire visible spectral range and exhibiting near-unity efficiencies. While the last years have seen rapid progress in green and red electroluminescence from CsPbX3 NCs, the development of blue counterparts remained rather stagnant. Controlling the surface state of CsPbX3 NCs had proven to be a major factor governing the efficiency of the charge injection and for diminishing the density of traps. Although didodecyldimethylammonium halides (DDAX; X = Br, Cl) had been known to improve the luminescence of CsPbX3 NCs when applied postsynthetically, they had not been used as the sole long-chain ammonium ligand directly in the synthesis of these NCs. Herein we report a facile, direct synthesis of DDAX-stabilized CsPbX3 NCs. We then demonstrate blue and green light-emitting diodes, characterized by the electroluminescence at 463-515 nm and external quantum efficiencies of 9.80% for green, 4.96% for sky-blue, and 1.03% for deep-blue spectral regions.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(a and b) Representative PL and absorbance (normalized on excitonic peak) spectra of DDAX-stabilized CsPb(Br1–xClx)3 NCs (inset is the photograph of the colloidal solutions of CsPb(Br1–xClx)3 NCs under UV-light excitation, λ=365 nm). (c) X-ray diffraction pattern of CsPbBr3 (green) and CsPb(Br1–xClx)3 (blue) and schematic illustration of the orthorhombic lattice of CsPb(Br1–xClx)3 NCs. The diffractograms are shifted vertically for clarity. (d and e) Transmission electron microscopy images of CsPb(Br1–xClx)3 NCs, for x = 0 and x = 0.24.
Figure 2
Figure 2
Performance of green-emissive LED with DDAB-capped CsPbBr3 NCs. (a) Energy levels of active layers of the device vs vacuum. (b) Current density and luminance vs applied bias. (c) EL spectra for various driving voltages. (d) External quantum efficiency vs current density through the active area.
Figure 3
Figure 3
(a and b) SEM cross-sectional image and corresponding schematic of the blue LED stack. (c) Work function of electrodes and band gap values of the different materials used in the LED stack, energies vs vacuum. (d) Current density and luminance of the devices with various EL peak positions as a function of voltage. (e and f) EQE of the devices with various EL peak positions as a function of current density and luminance.
Figure 4
Figure 4
(a) EL spectra of the LEDs. Legend reveals corresponding EL peak position. Inset shows photo of the EL of the operating device with Empa logo. (b) Commission Internationale de l’Éclairage CIE 1931 color diagram. Black triangle represents BT.2020 (Rec2020) color coordinates. Red dots mark coordinates of LEDs presented in this work.
See this image and copyright information in PMC

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