Highly efficient blue organic light-emitting diodes using quantum well-like multiple emissive layer structure

Abstract

In this study, the properties of blue organic light-emitting diodes (OLEDs), employing quantum well-like structure (QWS) that includes four different blue emissive materials of 4,4′-bis(2,2′-diphenylyinyl)-1,1′-biphenyl (DPVBi), 9,10-di(naphth-2-yl)anthracene (ADN), 2-(N,N-diphenyl-amino)-6-[4-(N,N-diphenyl amine)styryl]naphthalene (DPASN), and bis(2-methyl-8-quinolinolate)-4-(phenyl phenolato) aluminum (BAlq), were investigated. Conventional QWS blue OLEDs composed of multiple emissive layers and charge blocking layer with lower highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy level, and devices with triple emissive layers for more significant hole-electron recombination and a wider region for exciton generation were designed. The properties of triple emissive layered blue OLEDs with the structure of indium tin oxide (ITO) /N,N′-diphenyl-N,N′-bis(1-naphthyl-phenyl)-(1,1′-biphenyl)-4,4′-diamine (NPB) (700 Ǻ)/X (100 Ǻ)/BAlq (100 Ǻ)/X (100 Ǻ)/4,7-diphenyl-1,10-phenanthroline (Bphen) (300 Ǻ)/lithium quinolate (Liq) (20 Ǻ)/aluminum (Al) (1,200 Ǻ) (X = DPVBi, ADN, DPASN) were examined. HOMO-LUMO energy levels of DPVBi, ADN, DPASN, and BAlq are 2.8 to 5.9, 2.6 to 5.6, 2.3 to 5.2, and 2.9 to 5.9 eV, respectively. The OLEDs with DPASN/BAlq/DPASN QWS with maximum luminous efficiency of 5.32 cd/A was achieved at 3.5 V.

Modulating Excitonic Recombination Effects through One‐Step Synthesis of Perovskite Nanoparticles for Light‐Emitting Diodes

“…The energy levels of Bphen and the Ca/ Ag electrode were taken from the literature. [30,31] Ag entler slope( less steep)w as observed in 10 %O ABr devices in the trap-limitedc onduction regime, indicating slower charge transport caused by the existence of multiple grain boundaries in the carrier-transport path. As pace-chargelimited current regime (J % V 2 )w as observed above 4a nd 7.2 V for the 0% OABr and 10 %O ABr device, respectively (Figure S11).…”

“…Excitonic recombination-dominated decay processes were demonstrated by tailoring perovskite nanocrystalline films through ao ne-step in situ deposition method. This was achieved by systematic replacement of OABr (octyl ammonium bromide) for MABr (methyl ammonium bromide) in defined [30,31] corresponding (c) currentd ensity and luminance curve versusc haracteristicsvoltage, (d) currente fficiency (cd A À1 )v ersus current density,( e) EL spectra of the devices at different currentd ensity (mA cm À2 ). Inset shows photograph of nanoparticle perovskite-based LED working device.…”

“…[23][24][25] This furtherr estricts solution processing of subsequent device layers.C ommonly used long-chain organic capping/stabilizingl igands such as oleic acid and oleylamine can suppress charge injection, limit brightness, and result in high turn-on voltage in LED devices. [29][30][31] Thus, it is challenging to form ac ompact and ligandfree film from preformed nanoparticles. Am ore elegant approach would be to induce the in situ/one-step formation of perovskite nanocrystals during the film formation process.…”

Organic Light-Emitting Diodes Based on Phthalimide Derivatives: Improvement of the Electroluminescence Properties

“…Thus, a performant emitter investigated in a none-adapted structure will furnish only low electron-to-photon efficiencies. Face to this consideration, promising light-emitting materials such as Firpic [5], Ir(ppy) 3 [6], Ir(piq) 3 [7], DCJTB [8], MEH-PPV [9][10][11] or DPVBi [12] have been extensively studied in the literature so that some of these materials have been largely popularized by the number of publications devoted to their studies. Among emitters, phthalimide-based materials are an attractive class of materials by their good electron-transport abilities [13,14] and their remarkable electron-accepting ability [15,16].…”