Solution-processed white organic light-emitting diode based on a single-emitting small molecule

A pure-white organic light-emitting diode (WOLED) with a simple device architecture of indium tin oxide (ITO)/poly-(3,4-ethylenedioxythiophene):poly-(styrenesuphonic acid) (PEDOT:PSS)/L-Z-390/1,3,5-tri(N-phenylbenzimidazol-2-yl)benzene (TPBi)/LiF/Al was realized by using a single small molecule 3,3′-(2,7-Dis((9-(2,3,5,6-tetrafluorophenyl)-9H-carbazol-3-yl)ethynyl)-9H-fluorene-9,9-diyl)bis(9-heptyl-9H-carbazole) (L-Z-390) as the light-emitting material. The WOLED exhibited efficient white emission with a turn-on voltage of 6 V, a maximum luminous efficiency of 3.6 cd/A at 6 V, a maximum luminous of 204 cd/m2 at 13 V and Commission Internationale de l’Eclairage (CIE) coordinates of (0.33, 0.34). The device performance characteristics are among the best ever reported for solution-processed WOLEDs with a single-emitting small molecule. The white light comes from the combination of the blue emission originating from the excimer of L-Z-390 and the long-wavelength orange emission originating from the electromer of L-Z-390 under a high electric field. The double-layer device based on 3,3′-(2,7-Dis((9-(2,3,5,6-tetrafluorophenyl)-9H-carbazol-3-yl)ethynyl)-9H-fluorene-9,9-diyl)bis(9-(2,3,5,6-tetrafluorophenyl)-9H-carbazole) (L-Z-398), the other molecule with two more electron-withdrawing 2,3,5,6-tetrafluorophenyl units than L-Z-390, shows green EL under the high voltages. That L-Z-398 cannot form electromer under a high voltage may be because the L-Z-398 cannot stably form L-Z-398+ component and L-Z-398− component simultaneously due to the too strong electron-withdrawing ability of the four 2,3,5,6-tetrafluorophenyl units connected to each carbazole.