Organic–Inorganic Hybrid Device with a Novel Deep-Blue Emitter of a Donor–Acceptor Type, with ZnO Nanoparticles for Solution-Processed OLEDs

Abstract

Two new deep-blue emitters with bipolar properties based on an organoboron acceptor and carbazole donor were newly synthesized: 2-(9H-carbazol-9-yl)-5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho [3,2,1-de]anthracen-7-yl)-5H-benzo[b]carbazole (TDBA-BCZ) and 5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho [3,2,1-de]anthracen-7-yl)-8-phenyl-5,8-dihydroindolo[2,3-c]carbazole (TDBA-PCZ). The two emitters showed deep-blue and real-blue photoluminescence emission in their solution and film states, respectively. The doped spin-coated films were prepared using synthesized materials and showed a root-mean-square roughness of less than 0.52 nm, indicating excellent surface morphology. The doped devices, fabricated via a solution process using TDBA-BCZ and TDBA-PCZ as the dopants, showed electroluminescence peaks at 428 and 461 nm, corresponding to the Commission Internationale de L’éclairage (CIE) coordinates of (0.161, 0.046) and (0.151, 0.155), respectively. The external quantum efficiency (EQE)/current efficiency (CE) of the solution-processed forward devices, with TDBA-BCZ and TDBA-PCZ as dopants, were 7.73%/8.67 cd/A and 10.58%/14.24 cd/A, respectively. An inverted OLED device fabricated using rod-shaped ZnO nanoparticles as an electron injection layer showed a CE of 1.09 cd/A and an EQE of 0.30%.

Solution-Processed Metal Oxide Nanostructures for Carrier Transport

“…By using ZnO-OA/ZnO double ETLs with matched energy level alignment, the optimized CdSe QLED showed 5-9% enhancement in maximum luminance and 16-35% improvement in current efficiency when compared to the controlled device using single ZnO ETL. Kang et al incorporated ZnO NPs as the electron-injection layer in deep-blue OLEDs [6], using two new molecules, 2-(9H-carbazol-9-yl)-5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1de]anthracen-7-yl)-5H-benzo[b]carbazole (TDBA-BCZ) and 5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-8-phenyl-5,8-dihydroindolo[2,3-c] carbazole (TDBA-PCZ), as the emitters. The ZnO NP layer composed of dense spherical particles was obtained by spin coating from a commercial ZnO NP solution.…”