Abstract
To realize power efficient solution-processed phosphorescent organic light-emitting diodes (s-PhOLEDs), the corresponding high driving voltage issue should be well solved. To solve it, efforts have been devoted to the exploitation of novel host or interfacial materials. However, the issues of charge trapping of phosphor and/or charge injection barrier are still serious, largely restraining the power efficiency (PE) levels. Herein, with the utilization of an exciplex-forming couple 4, 4′, 4″ -tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) and 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB), the efficient charge injection and transporting, barrier-free hole-electron recombination for the formation of the interfacial exciplex, and elimination of charge traps of phosphors in the emissive layer are realized simultaneously, resulting in a turn-on voltage of 2.36 V, a record high PE of 97.2 lm W−1, as well as extremely low driving voltage of 2.60 V at 100 cd m−2, 3.03 V at 1000 cd m−2 and 4.08 V at 10000 cd m−2. This report is the first time that the PE performance of s-PhOLED approaches 100 lm W−1 high level, even superior to the corresponding state-of-the-art performance of the same color vacuum-deposited PhOLED (v-PhOLED) counterpart. We anticipate this report opens a new avenue for achieving power efficient monochromatic and white s-PhOLEDs with simple structures.
Highlights
Phosphorescent organic light-emitting diodes (PhOLEDs)[1] have attracted much attention since they can harvest both singlet and triplet excitons to realize a nearly 100% internal quantum efficiency
The key problem responsible for the poor power efficiency (PE) in s-PhOLEDs is their high driving voltages, which may result from the large charge injection barrier[31], low charge mobility[32,33], heterojuction barrier necessary for the generation of bulk exciton[34,35] and intense charge-trapping behavior of a phosphor in the emissive layer (EML)[36,37] etc
We develop a solution-processed yellow-emitting electrophosphorescent device with a record high PE of 97.2 lm W−1 (25.2%, 74.3 cd A−1) by the combination of 4, 4′, 4′′ -tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) and 1,3,5-tri(m-pyrid-3-yl-phenyl) benzene (TmPyPB) as an exciplex-forming couple
Summary
Phosphorescent organic light-emitting diodes (PhOLEDs)[1] have attracted much attention since they can harvest both singlet and triplet excitons to realize a nearly 100% internal quantum efficiency. The key problem responsible for the poor PE in s-PhOLEDs is their high driving voltages, which may result from the large charge injection barrier[31], low charge mobility[32,33], heterojuction barrier necessary for the generation of bulk exciton[34,35] and intense charge-trapping behavior of a phosphor in the emissive layer (EML)[36,37] etc To address these limitations, many strategies have been developed in v-PhOLEDs, such as the p-i-n structure[38], cascade charge injection/transport multilayers[2], and exciplex-forming co-host[14]. Systematic research about the device operating mechanism will be performed subsequently, which can give us a clear picture of our concept
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