Non-doped hot-exciton blue organic light-emitting diodes with efficiency over 20
Mingke Li1, Yulong Li1, Yue Yu1,2
1Institute of Polymer Optoelectronic Materials and Devices, Guangdong Basic Research Center of Excellence for Energy and Information Polymer Materials, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China.
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Host-guest doping is the mainstream technology for organic light-emitting diodes (OLEDs). Non-doped OLEDs, using a single material for both electron migration and exciton luminescence, promise simplified preparation, but lack efficient emitting-layer materials due to the concentration quenching of excitons (especially long-lifetime triplet excitons). This study compares two novel isomeric emitters (pTCN and mTCN) based on the hot-exciton mechanism. It shows that thermodynamically favorable excited-state alignments enable efficient high-lying reverse intersystem crossing (hRISC) from high-lying triplet states (Tn, n ≥ 2) to singlet states (S 1) with ΔETn - S 1 > 0. The pTCN-based non-doped device exhibited an unprecedented maximum external quantum efficiency (EQEmax) of 20.3% with CIE coordinates of (0.15, 0.07), while mTCN (unfavorable ΔETn - S 1 < 0) only has 5.3% EQEmax. Photophysical and excited-state dynamics studies confirm that the difference between the rates of the hRISC processes (∼1 × 108 vs. 0.7 × 108 s-1) gives rise to this performance gap.
