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Higher Order Effects in Organic LEDs with Sub-bandgap Turn-on

Published

Author(s)

Sebastian Engmann, Adam J. Barito, Emily G. Bittle, Chris Giebink, Lee J. Richter, David J. Gundlach

Abstract

Spin-dependent nonlinear processes in organic materials such as singlet-fission and triplet- triplet annihilation could increase the performance for photovoltaics, detectors, and light emitting diodes. Rubrene/C60 light emitting diodes exhibit a distinct low voltage (half- bandgap) threshold for emission. Two origins for the low voltage turn-on have been proposed: (i) Auger assisted energy up-conversion, and (ii) triplet-triplet annihilation. We test these proposals by systematically altering the rubrene/C60 interface kinetics by introducing thin interlayers. Quantitative analysis of the unmodified rubrene/C60 device suggests that higher order processes can be ruled out as the origin of the sub-bandgap turn-on. Rather, band-to-band recombination is the most likely radiative recombination process. However, insertion of a bathocuproine layer yields a 3-fold increase in luminance compared to the unmodified device. This indicates that suppression of parasitic interface processes by judicious modification of the interface allows a triplet-triplet annihilation channel to be observed.
Citation
Nature Communications

Keywords

Triplet-Triplet-Annihilation, Triplet-Fusion, Auger Recombination, Half-Bandgap, Organic Light Emitting Diodes, Small molecule
Created January 16, 2019, Updated January 27, 2020