Efficient radical-based light-emitting diodes with doublet emission
Top Cited Papers
- 21 November 2018
- journal article
- research article
- Published by Springer Science and Business Media LLC in Nature
- Vol. 563 (7732), 536-540
- https://doi.org/10.1038/s41586-018-0695-9
Abstract
Organic light-emitting diodes (OLEDs)(1-5), quantum-dot-based LEDs(6-10), perovskite-based LEDs(11-13) and micro-LEDs(14,15) have been championed to fabricate lightweight and flexible units for next-generation displays and active lighting. Although there are already some high-end commercial products based on OLEDs, costs must decrease whilst maintaining high operational efficiencies for the technology to realise wider impact. Here we demonstrate efficient action of radical-based OLEDs(16), whose emission originates from a spin doublet, rather than a singlet or triplet exciton. While the emission process is still spin-allowed in these OLEDs, the efficiency limitations imposed by triplet excitons are circumvented for doublets. Using a luminescent radical emitter, we demonstrate an OLED with maximum external quantum efficiency of 27 per cent at a wavelength of 710 nanometres-the highest reported value for deep-red and infrared LEDs. For a standard closed-shell organic semiconductor, holes and electrons occupy the highest occupied and lowest unoccupied molecular orbitals (HOMOs and LUMOs), respectively, and recombine to form singlet or triplet excitons. Radical emitters have a singly occupied molecular orbital (SOMO) in the ground state, giving an overall spin-1/2 doublet. If-as expected on energetic grounds-both electrons and holes occupy this SOMO level, recombination returns the system to the ground state, giving no light emission. However, in our very efficient OLEDs, we achieve selective hole injection into the HOMO and electron injection to the SOMO to form the fluorescent doublet excited state with near-unity internal quantum efficiency.Keywords
This publication has 30 references indexed in Scilit:
- Quantum‐Dot Light‐Emitting Diodes for Large‐Area Displays: Towards the Dawn of CommercializationAdvanced Materials, 2017
- High-efficiency light-emitting devices based on quantum dots with tailored nanostructuresNature Photonics, 2015
- Solution-processed, high-performance light-emitting diodes based on quantum dotsNature, 2014
- Highly efficient organic light-emitting diodes from delayed fluorescenceNature, 2012
- Bright, multicoloured light-emitting diodes based on quantum dotsNature Photonics, 2007
- Efficient Near-Infrared Polymer Nanocrystal Light-Emitting DiodesScience, 2002
- Highly efficient phosphorescent emission from organic electroluminescent devicesNature, 1998
- Electroluminescence from triplet metal—ligand charge-transfer excited state of transition metal complexesSynthetic Metals, 1998
- Light-emitting diodes based on conjugated polymersNature, 1990
- Organic electroluminescent diodesApplied Physics Letters, 1987