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

## TL;DR

Researchers developed non-doped blue OLEDs with over 20% efficiency using a new hot-exciton mechanism, simplifying device fabrication.

## Contribution

The study introduces a novel hot-exciton mechanism enabling efficient non-doped blue OLEDs with record efficiency.

## Key findings

- pTCN-based non-doped devices achieved 20.3% external quantum efficiency.
- mTCN devices showed only 5.3% efficiency due to unfavorable excited-state alignments.
- hRISC rates directly impact device performance, confirmed through photophysical studies.

## Abstract

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 (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 between the rates of the hRISC processes (∼1 × 108 vs. 0.7 × 108 s–1) gives rise to this performance gap.

Via the hot exciton mechanism, this study rapidly harnesses high-energy triplet excitons to realize ultra-high-efficiency non-doped blue OLEDs and simplify device fabrication processes.