High-performance solution-processed blue OLEDs based on “hot exciton” materials

Abstract

“Hot exciton” luminescent materials are being researched as potential candidates for application in OLEDs due to their ability to undergo high-level reverse intersystem crossing (hRISC). While evaporated OLEDs using “hot exciton” luminescent materials have shown impressive efficiency, there is a dearth of information on solution-processed “hot exciton” OLEDs, specifically in the realm of deep blue OLEDs. In this work, we developed novel solution-processed blue OLEDs by employing “hot exciton” material, 2-(4-(10-(3-(9H-carbazol-9-yl)phenyl) anthracen-9-yl)phenyl)-1-phenyl-1H-phenanthro [9,10-d] imidazole (PAC), as the luminescent material and host material (the classical fluorescent material BD as a guest). An improvement to the quantum efficiency of the luminescent layer was achieved by incorporating a hole transport layer (PVK) between the hole injecting layer (PEDOT:PSS:PFI) and the luminescent layer. Finally, the resultant non-doped blue OLED achieved EQEmax and EUEmax of 4.5 % and 56.3 %, respectively, while the doped blue OLED showed EQEmax and EUEmax of 5.3 % and 54.8 %, respectively. The efficiency roll-off at a brightness of 1000 cd m−2 for the doped device was 11.5 %, whereas for the non-doped device was only 4.2 %. Analysis of the magneto-electroluminescence and transient EL decay suggests that the high EUE in the solution-processed devices primarily derives from the “hot exciton” process. This study confirms that “hot exciton” materials can serve as a key factor in achieving efficient solution-processed blue OLEDs through a well-designed device architecture.