17 December 1999 Current voltage characteristics of organic EL devices with a Cu-phthalocyanine buffer layer
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A buffer layer is often placed between an ITO (indium-tin- oxide) electrode and a hole transport layer (HTL) of organic EL devices made of low-molecular-weight materials. Cu- phthalocyanine is the representative material of the buffer layer. Form the analysis of the current-voltage properties of the devices, we found that buffer layer hinders the current when it is very thin, 60 nm or less. On the other hand, when it is thick, it enhances the current. In order to clarify these effects of the buffer layer, we studied the hole injection process from the ITO electrode into the HTL in devices with and without the buffer layer. The results indicate that the holes are accumulated at the buffer layer/HTL interface because of the energy gap. These holes are injected into the HTL across the barrier. However, some of the holes are back transferred to the ITO. This rate is dependent on the thickness of the buffer layer and the voltage applied to the devices. The competition between forward and backward movements of the accumulated holes determines the current- voltage characteristics of the organic EL devices.
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Michio Matsumura, Michio Matsumura, Yuichiro Miyamae, Yuichiro Miyamae, } "Current voltage characteristics of organic EL devices with a Cu-phthalocyanine buffer layer", Proc. SPIE 3797, Organic Light-Emitting Materials and Devices III, (17 December 1999); doi: 10.1117/12.372721; https://doi.org/10.1117/12.372721

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