Abstract
Deep blue emission is crucial for achieving high-quality displays and lightings, while high-efficiency is required to enable the corresponding products energy-saving. Wet- and dry-process feasible efficient deep-blue emitter is highly desired to realize, respectively, low cost roll-to-roll fabrication of large area and high performance devices with precise deposition of organic layers. In this study, we demonstrate high efficiency ultra-deep blue and deep-blue organic light-emitting diodes (OLEDs) using cyanofluorene acetylene conjugate based emitters. Their results and discussion will be shown in two parts. In the first part, we present high-efficiency and ultra-deep blue OLEDs using a cyanofluorene-acetylene conjugate based emitter, 7,7' ((9,9-dibutyl- 9H-fluorene-2,7-diyl)bis(ethyne-2,1-diyl))bis(9,9-dipropyl-9H-fluorene-2 carbo-nitrile) (C3FLA-2). By spin coating, the C3FLA-2 shows maximum external quantum efficiency (EQE) of 6.1%, and at 100 cd m-2 for example, its color coordinates are (0.156, 0.055) with an EQE of 5.8%, the highest among all reported wet-processed deep-blue devices of fluorescent, phosphorescent, and thermally activated delayed fluorescent types. By vapor deposition, the device shows maximum EQE of 8.0%, and at 100 cd m-2 color coordinates of (0.156, 0.048) with EQE of 6.5%, the highest among all the dry-processed counterparts. The record high efficiency may be attributed to the emitter having high quantum yield of 86%, low doping concentration preventing concentration quenching, and a suitable host facilitating an effective host-to-guest energy transfer. In the second part, we also demonstrate a high efficiency deep-blue OLED using wet-process feasible donor-acceptor-type cyanofluorene acetylene conjugate based emitter, 7-(2-(9,9-dipropyl-9H-fluoren-2-yl)ethynyl)-9,9-dipropyl -9H-fluorene-2-carbonitrile (CFLA-DPA). In the doped solution-processed OLED device with 4,4’-bis(9H-carbazol-9-yl)biphenyl (CBP) host, the CFLA-DPA shows a maximum efficacy of 5.6 lm W-1, a maximum current efficiency of 5.4 cd A-1, a maximum EQE of 4.4%, and a peak luminance of 4150 cd m-2 with color coordinates of (0.15, 0.11). The resultant power efficiency is highest among all formerly reported solution-processed deep-blue OLED devices. The high efficacy may be attributed to the emitter having bipolar characteristic which may help to transport the injected carriers and a suitable host facilitating an effective host-to-guest energy transfer.