Enabling a 6.5% External Quantum Efficiency Deep-Blue Organic Light-Emitting Diode with a Solution-Processable Carbazole-Based Emitter

Abstract

Highly efficient deep-blue emission is crucial to realize energy-efficient and high-quality display and solid-state lighting applications. A solution-processable deep-blue emitter is essential for producing cost-effective large-area devices via roll-to-roll fabrication. Here, we demonstrate a highly efficient solution-processable deep-blue organic light-emitting diode by utilizing a carbazole-based fluorescent emitter 6-((9,9-dibutyl-7-((7-cyano-9-(2-ethylhexyl)-9H-carbazol-2-yl)­ethynyl)-9H-fluoren-2-yl)­ethynyl)-9-(2-ethylhexyl)-9H-carbazole-2-carbonitrile (JV55). The resultant device showed a maximum external quantum efficiency (EQE) of 6.5% and an EQE of 5.5% at 100 cd/m2 with CIE coordinates of (0.16, 0.06). The optimized device showed a maximum EQE of 6.5%. Additionally, the deep-blue emission also realized a 101% color saturation according to the NTSC standard. The high efficiency may be attributed to engineering appropriate device architecture and enabling balanced carrier injection, effective host-to-guest energy transfer, the emissive layer having a very high quantum yield of 91%, utilizing a host with high triplet energy so as to confine exciton on the guest, and low doping concentration inhibiting efficiency roll-off due to concentration quenching.

Decoration of Dibenzofuran Using Cyanocarbazole via 6‐Position as a Molecular Design Approach for High‐Triplet‐Energy Bipolar Host Materials

“…The computed HOMO, LUMO, and HOMO–LUMO band gaps ( E g ) of the compounds were −5.60 eV, −1.19 eV, and 4.41 eV, respectively, for mBFCzCN and −5.46 eV, −1.22 eV and 4.24 eV for dBFCzCN . The relative trends of the theoretically estimated and experimentally measured HOMO, LUMO, and E g values were in agreement with each other …”

“…The connectiono ft wo cyanocarbazole units via the 6-position of carbazole restricted the extension of the LUMO into the cyanocarbazole unit, which reduced the chargeh opping integral for electron transport. [19] Therefore, the Jo ft he EOD device was decreased in the dBFCzCN device. The single carrier device density of the mBFCzCN and dBFCzCN can be correlated with the Jo ft he blue and green PhOLEDs, respectively.T he FIrpic doped blue and Ir(ppy) 3 doped green PhOLEDsa re differenti nt he charge trapping process.…”

Color-Tunable Organic Light Emitting Diodes for Deep Blue Emission by Regulating the Optical Micro-Cavity

“…According to Equations (6)- (13), Figure 6C-E shows the simulated reflectivity, transmissivity of the Ag layer with 5 nm-, 10 nm-, 15 nm-and 20 nm-thickness and of 100 nm-thick Al, as well as their phase shifts. Then, the simulated complex dielectric constants ε and complex refractive index ñ of Ag and Al are shown in Figure 6A,B, in which ε 1 and ε 2 is the real and the imaginary part of ε, and n and κ is the ordinary refractive index and the extinction coefficient, respectively.…”

“…According to Equations (6)- (13), Figure 6C-E shows the simulated reflectivity, transmissivity of the Ag layer with 5 nm-, 10 nm-, 15 nm-and 20 nm-thickness and of 100 nm-thick Al, as well as their phase shifts.…”

“…Kondo et al reported a thermally activated delayed-fluorescence material that exhibits ultrapure blue emission, whose devices emit light at 469 nm with a full-width at half-maximum of 18 nm with an external quantum efficiency of 34.4% at the maximum and 26.0% at 1000 cd m −2 [12]. However, all these saturated deep-blue organic materials for full-color flat-panel displays have a deep energy level (HOMO) and a very wide band-gap [13,14]. It is quite difficult to design their molecular structure with a good carrier mobility and environment stability [15].…”