Non-doped hot exciton blue organic light-emitting diodes with efficiency over 20%

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 concentration quenching of excitons (especially long-lifetime triplet excitons). This study compares two novel isomeric emitters (pTCN, 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 state (S1) with ΔETn−S1 > 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−S1 < 0) only has 5.3% EQEmax. Photophysical and excited-state dynamics studies confirm that the difference in the rate of hRISC processes (∼1×108 s–1 vs. 0.7×108 s–1) gives rise to this performance gap.