Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 7, Issue 4, Pages 2972-2978Publisher
AMER CHEMICAL SOC
DOI: 10.1021/am508574m
Keywords
exciton utilization; reverse intersystem crossing; triplet-triplet annihilation; electroluminescence; magnetoelectroluminescence
Funding
- National Natural Science Foundation (NSF) of China [61275036, 21221063, 91233113]
- MOST [2015CB655000]
- Fundamental Research Funds for the Central Universities [SWU114042, XDJK2015C046]
- SCUT
- NSFC [2014ZG0009, 51173051, U1301243]
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The discovery of triplet excitons participating in the photoluminescent processes in a growing number of pure organic emitters represents an exciting impetus for a diversity of promising opto, bio, and optoelectronic applications. In this contribution, we have studied a small-molecule dithienylbenzothiadiazole-based red-emitting dye red-1b, which shows clearly delayed fluorescence under optical and electrical excitation. The OLED device that contained red-1b as a nondoped solution-processable emitter exhibited a moderately high utilization of exciton amounting to 31% and slow efficiency roll-off. Magnetoelectroluminescence measurements revealed the coexistence of reverse intersystem crossing from the lowest triplet state to singlet state (RISC, E-type triplet to singlet up-conversion) and triplettriplet annihilation (TTA, P-type triplet to singlet up-conversion). Specifically, in low current-density regime, the moderately high exciton utilization is attributed to RISC (i.e., thermally activated delayed fluorescence, TADF), whereas in high current-density regime, TTA may contribute to suppressing efficiency roll-off. Furthermore, the results showed that red-1b may represent a new kind of organic red emitters that display delayed fluorescence in a way differing from the few red emitters investigated so far.
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