13 September 2012 Characterization of charge carrier injection in organic and hybrid organic/inorganic semiconductor devices by capacitance-voltage measurements
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Abstract
Organic and hybrid organic / inorganic semiconductor heterostructures offer great potential as key technology for cost-efficient electro-photonic devices. To exploit their full potential, fundamental understanding of charge carrier injection is essential. Therefore we use current-luminance-voltage (I-L-V) and capacitance-voltage (C-V) measurements to analyze the injection characteristics of monochrome OLED test structures and hybrid organic / inorganic (HOI) pentacene / n-GaN and Alq3 / n-GaN heterostructures processed by organic vapor phase deposition (OVPD) and metal organic chemical vapor deposition (MOCVD), respectively. In a first step, we fundamentally analyze the specific C-V characteristics of OLED test structures. The multilayer devices show additional features in the C-V profile as compared to the bilayer OLED investigated by Brütting et al.1,2. We attribute this behavior to the additional organic / organic interfaces and the resulting energetic barriers in multilayer devices. In addition, we compared the C-V measurements of pristine and degraded OLED test structures. Here we conclude that a deterioration of hole injection in degraded devices is dominant, whereas electron injection remains largely unaffected. Furthermore, in pristine and degraded OLED, increased temperatures generally lead to improved charge injection as well as a reduced impact of the additional barriers in multilayer stacks. By analyzing I-V and C-V measurements of HOI heterostructures, we find ambipolar currents in pentacene-based diodes with electrons from n-GaN being injected at lower bias than the onset of hole injection from the gold anode contacts. Generally, I-V measurements of both types of HOI heterostructures show an onset of charge injection at very low bias voltage. Accordingly, n-GaN offers superior electron injection characteristics recommending n-GaN as cathode contact e.g. in fully transparent OLED microdisplays.
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M. Weingarten, M. Weingarten, M. Slawinski, M. Slawinski, F. Urbain, F. Urbain, D. Fahle, D. Fahle, D. Bertram, D. Bertram, M. Heuken, M. Heuken, H. Kalisch, H. Kalisch, A. Vescan, A. Vescan, } "Characterization of charge carrier injection in organic and hybrid organic/inorganic semiconductor devices by capacitance-voltage measurements", Proc. SPIE 8476, Organic Light Emitting Materials and Devices XVI, 84761H (13 September 2012); doi: 10.1117/12.929582; https://doi.org/10.1117/12.929582
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