Morphologically controlled charge injection and transport of the organic semiconductors in controlled nano-meter regime

MasterThe possibility of using small molecules and polymeric organic semiconductor materials for applications in the electronics has been of great scientific and technological interest for several decades. Recently, the needs for flexible electronics such as flexible displays, radio frequency identification (RFID) tag and smart cards have found the significance of this practical impact in optoelectronic applications. In the past 10 years, intensive studies have been conducted by many researchers and the research area was also broadened for the commercial application of these materials to organic thin-film electronic devices such as memory, photovoltaics, organic light emitting diodes (OLEDs) and organic thin-film transistors (OTFTs). The impressive improvement in device performance and efficiency of organic electronics has been successively reported. The performance of organic thin film transistors (OTFT) using small molecules has considerably improved during the last couple of decades. Organic materials have the superior advantages of potentially simple and low-temperature thin-film processing, using spin coating technology, ink-jet printing or stamping. This fact suggests that OTFTs could be a competitive material for applications that need large-area coverage, low-temperature processing and low cost. [1-2]But, in the aspect of device performances, OTFTs is not suitable for the applications requiring high switching speeds due to its low field effect mobility. Approach to overcoming these serious limitations is to imitate the approach of improving performance by downscaling which the silicon industry has adopted for the last 40 years and reducing the contact resistance between the organic semiconductors and the metal electrodes.In this study, we have compared the performance of the OTFTs in confined micro- and nano relief patterns using soft lithographic methods with that of the standard OTFTs using vacuum deposited films. And we have investigated the difference of charge transport along the relief of the substrate from the perpendicular direction. We have analyzed the effect of the morphology of the organic semiconductor films confined in the relief patterns on the charge transport. So far, many research groups don`t have enough understanding of the morphology effect on the charge transport in nano region. The other study shows that the charge injection barrier is controlled by introducing a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS):PFI high conducting polymer as electrodes. Deposition of polymeric electrode layers including a perfluorinated ionomer (PFI) has been demonstrated using layer-by-layer spin self-assembly for enhanced device performance. We show that the layer-by-layer spin self-assembled thin films enable to control work functions of electrodes of the OFET by changing the PFI concentration and improved surface roughness on the metal electrodes. In consequence, the smaller charge injection barrier and reduced hysteresis are observed in the OFET using PEDOT:PSS:PFI polymeric electrodes