Exciton-induced degradation of organic/electrode interfaces in ultraviolet organic photodetectors |
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Authors: | Qi Wang Hany Aziz |
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Affiliation: | Department of Electrical & Computer Engineering, and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo Ontario N2L 3G1, Canada |
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Abstract: | We study the degradation mechanisms of ultraviolet (UV) organic photodetectors (OPDs). Contrary to expectations, we determine that the bulk of the organic layers in UV OPDs is stable under prolonged UV irradiation, showing no detectable changes in photophysical characteristics such as photoluminescence yield and exciton lifetime and thus not contributing to the observed degradation behavior of UV OPDs. However, the results show that the organic/electrode interfaces in UV OPDs, including indium tin oxide (ITO)/organic and organic/metal ones, are susceptible to UV irradiation, leading to a deterioration in both charge injection and extraction across the interfaces. The degradation of the organic/electrode interfaces in UV OPDs is essentially induced by UV-generated excitons in their vicinity and may be responsible for nearly 100% of the photo-current loss of UV OPDs. Approaches for improving the photo-stability of organic/electrode interfaces, and thus the lifetime of UV OPDs, are also investigated. We demonstrate that the use of thin (∼0.5 nm) interfacial layers such as lithium acetylacetonate at organic/metal interfaces can significantly reduce the interfacial degradation, and the use of appropriate hole transport materials such as N,N′-bis (naphthalen-1-yl)-N,N′-bis(phenyl) benzidine at ITO/organic interfaces can greatly improve the interfacial photo-stability. |
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Keywords: | Exciton-induced degradation Organic/electrode interfaces Ultraviolet (UV) organic photodetectors (OPDs) Interfacial layers |
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