Efficient near-infrared organic light-emitting diodes with emission from spin doublet excitons
Hwan‐Hee Cho, Sebastian Gorgon, Giacomo Londi, Samuele Giannini, Changsoon Cho, Pratyush Ghosh, Claire Tonnelé, David Casanova, Yoann Olivier, Tomi K. Baikie, Feng Li, David Beljonne, Neil C. Greenham, Richard H. Friend, Emrys W. Evans
Abstract
The development of luminescent organic radicals has resulted in materials with excellent optical properties for near-infrared emission. Applications of light generation in this range span from bioimaging to surveillance. Although the unpaired electron arrangements of radicals enable efficient radiative transitions within the doublet-spin manifold in organic light-emitting diodes, their performance is limited by non-radiative pathways introduced in electroluminescence. Here we present a host-guest design for organic light-emitting diodes that exploits energy transfer with up to 9.6% external quantum efficiency for 800 nm emission. The tris(2,4,6-trichlorophenyl)methyl-triphenyl-amine radical guest is energy-matched to the triplet state in a charge-transporting anthracene-derivative host. We show from optical spectroscopy and quantum-chemical modelling that reversible host-guest triplet-doublet energy transfer allows efficient harvesting of host triplet excitons.