# High‐Efficiency TADF Dendritic Emitters Enabled by Synchronously Inhibiting Degenerated Triplet Excited States and Structural Relaxation Toward Solution‐Processed OLEDs with EQE Over 33%

## TL;DR

Scientists designed a new type of light-emitting material that improves the efficiency of organic light-emitting diodes (OLEDs) by using an asymmetrical structure to enhance light emission.

## Contribution

The novel contribution is the design of an asymmetrical TADF dendrimer that achieves high photoluminescence efficiency and record OLED performance.

## Key findings

- The asymmetrical TADF dendrimer DMAC-XT-TCz achieves near-unity photoluminescence efficiency.
- Solution-processed OLEDs using DMAC-XT-TCz reach an external quantum efficiency of 33.7%.
- Using DMAC-XT-TCz as a sensitizer boosts performance in narrowband OLEDs with a current efficiency of 117.7 cd A⁻¹.

## Abstract

Manufacturing high‐performance solution‐processed organic light‐emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) dendritic emitters remains a formidable challenge due to the lack of efficient TADF dendrimers. Herein, a symmetry breaking strategy is adopted to construct an asymmetrical TADF dendrimer denoted as DMAC‐XT‐TCz. An in‐depth analysis of the photophysical properties combining with theoretical calculation expose that the asymmetrical architecture of target emitter switches degenerated triplet excited states to isolated counterpart, thereby effectively breaking the degeneracy of vibrational levels and boosting the spin flip of triplet excitons. Additionally, the nonradiative decay is also suppressed due to imbedding oxygen linkage to locking electron‐donating skeleton. Thus, near‐unity photoluminescence efficiency and excellent reverse intersystem crossing rate of 7.8 × 105 s−1 can be achieved for DMAC‐XT‐TCz. Impressively, the optimized solution‐processed OLEDs achieve an attractive external quantum efficiency of 33.7%, which is the highest value for TADF dendrimer‐based OLEDs. By using DMAC‐XT‐TCz as sensitizer, the solution‐processed narrowband OLEDs based on a multiple‐resonance TADF emitter also acquire record‐high device performances with current efficiency of 117.7 cd A−1. This study highlights the significance of asymmetric architecture in designing high‐efficiency TADF dendrimer, and provides an effective strategy to boost solution‐processed narrowband OLEDs through adopting TADF dendrimer as sensitizer.

Asymmetrical thermally activated delated fluorescence dendritic emitters are delicately constructed through symmetry breaking strategy, and near‐unity photoluminescence efficiency and excellent reverse intersystem crossing process are achieved via breaking the degeneracy of vibrational levels and boosting the spin flip of triplet excitons. The optimized solution‐processed organic light emitting dioses achieve a record‐high external quantum efficiency of 33.7%.