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Singlet and triplet to doublet energy transfer: improving organic light-emitting diodes with radicals
Nature Communications, Volume: 13, Issue: 1
Swansea University Author: Emrys Evans
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DOI (Published version): 10.1038/s41467-022-29759-7
Organic light-emitting diodes (OLEDs) must be engineered to circumvent the efficiency limit imposed by the 3:1 ratio of triplet to singlet exciton formation following electron-hole capture. Here we show the spin nature of luminescent radicals such as TTM-3PCz allows direct energy harvesting from bot...
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Organic light-emitting diodes (OLEDs) must be engineered to circumvent the efficiency limit imposed by the 3:1 ratio of triplet to singlet exciton formation following electron-hole capture. Here we show the spin nature of luminescent radicals such as TTM-3PCz allows direct energy harvesting from both singlet and triplet excitons through energy transfer, with subsequent rapid and efficient light emission from the doublet excitons. This is demonstrated with a model Thermally-Activated Delayed Fluorescence (TADF) organic semiconductor, 4CzIPN, where reverse intersystem crossing from triplets is characteristically slow (50% emission by 1 µs). The radical:TADF combination shows much faster emission via the doublet channel (80% emission by 100 ns) than the comparable TADF-only system, and sustains higher electroluminescent efficiency with increasing current density than a radical-only device. By unlocking energy transfer channels between singlet, triplet and doublet excitons, further technology opportunities are enabled for optoelectronics using organic radicals.
Faculty of Science and Engineering
J.D., Z.C. and F.L. are grateful for financial support from the National Natural Science Foundation of China (grant no. 51925303). E.W.E. is grateful to the Leverhulme Trust for an Early Career Fellowship; and the Royal Society for a University Research Fellowship (grant no. URF\R1\201300). TJHH thanks the Royal Society for a University Research Fellowship (grant no. URF\R1\201502). WKM and the Centre for Advanced Electron Spin Resonance is supported by EPSRC (EP/L011972/1). F.L. is an academic visitor at the Cavendish Laboratory, Cambridge, and is supported by the Talents Cultivation Programme (Jilin University, China). A.J.G. and RHF acknowledge support from the Simons Foundation (grant no. 601946) and the EPSRC (EP/M01083X/1 and EP/M005143/1). This project has received funding from the ERC under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 670405 and 101020167).