Study On The Effect Of Electrode Buffer Layer To Improve The Performance Of Organic Thin Film Transistor

This paper studies how to improve the performance of pentacene thin film transistors by inserting an electrode buffer layer and the performance improvement mechanism. When the source and drain electrodes contact with pentacene active layer, due to the interfacial dipole layer and metallic semiconductor layer, the contact interface will generate a1eV hole injection barrier, this barrier decline hole injection efficiency and reduce device performance. Using source and drain electrode buffer layer, on the one hand can block the diffusion of gold in the organic layer, avoiding Metallic organic layer; on the other hand inhibit the formation of interfacial dipole layer to some extent. In this paper, first, gold and pentacene contact interface properties were studied; secondly use Bphen modified the source and drain electrode of organic thin film transistor; Finally, to further enhance the performance of the device using the P‐type buffer layer materials modified source and drain electrodes, the device performance has been further improved. Details are as follows:1、Polyvinyl methyl organic polymer (PMMA) was prepared as an insulating layer material of the organic thin film transistor pentacene, realization of the preparation of full organic devices. The contact interface of gold source and drain electrodes and the pentacene active layer were analyzed. Analysis derived, grown under thermal evaporation of gold source and drain, gold penetrates into pentacene organic active layer forming a metalic layer that causes a hole injection barrier between gold and pentacene. Furthermore there is also an interface dipole layer, the presence of the dipole layer is also led to the hole injection barrier. The combined effect of two factors result in the formation of an approximately1eV interface hole injection barrier. The organic thin film transistor performance is deteriorated.2、Using Bphen buffer layer modified the aource and drain electrodes of organic thin film transistor, and compare with conventional inorganic buffer layer lithium fluoride. We found that Bphen is a better buffer layer material and easy to realize low‐temperature preparation. The thickness of Bphen buffer layer is optimized. We found that: When the buffer layer is thicker (5nm), the carrier is not sufficient to penetrate the buffer layer by tunneling effect; When the thickness of the buffer layer is thinner, continuous and dense film can not be formed above the active layer. Finally, the device with3nm Bphen buffer layer obtained an enhanced mobility of0.3cm2/Vs and a decreased threshold voltage of‐31.2V.3、To further enhance the performance of the device, using P‐type material buffer layer in place of Bphen buffer layer. Molybdenum oxide is used herein as a dopant, doping in Pentacen m‐MTDATA and m‐MTDATA doped pentacene, respectively. Three materials doped device exhibit the most superior performance. There are two reasons: first is that the layer surface is dense, smooth, and can block the diffusion of gold in the pentacene active layer and suppress the formation of metalic layer; Second, the charge transfer complex can be formed to facilitate hole injection. Using P doped buffer layer can greatly improve the performance of organic thin film transistor, the device obtained an enhanced mobility of0.72cm2/Vs and a decreased threshold voltage of‐13.4V.