Highly efficient light-emitting diodes based on intramolecular rotation

TL;DR

This paper introduces a new class of organic light-emitting diodes that utilize intramolecular rotation to tune singlet-triplet energy gaps, achieving near-100% internal quantum efficiency and surpassing traditional OLED performance.

Contribution

It demonstrates a novel molecular design enabling efficient light emission by controlling singlet-triplet energy gaps through intramolecular rotation.

Findings

Achieved near-100% internal quantum efficiency.

Demonstrated high current and power efficiencies (87 cd/A, 75 lm/W).

Produced solution-processed LEDs outperforming some vacuum-processed devices.

Abstract

The efficiency of an organic light-emitting diode (OLED) is fundamentally governed by the spin of recombining electron-hole pairs (singlet and triplet excitons), since triplets cannot usually emit light. The singlet-triplet energy gap, a key factor for efficient utilization of triplets, is normally positive. Here we show that in a family of materials with amide donor and carbene acceptor moieties linked by a metal, this energy gap for singlet and triplet excitons with charge-transfer character can be tuned from positive to negative values via the rotation of donor and acceptor about the metal-amide bond. When the gap is close to zero, facile intersystem crossing is possible, enabling efficient emission from singlet excitons. We demonstrate solution-processed LEDs with exceptionally high quantum efficiencies (near-100% internal and >27% external quantum efficiencies), and current and power efficiencies (87 cd/A and 75 lm/W) comparable to, or exceeding, those of state-of-the-art vacuum-processed OLEDs and quantum dot LEDs.