| Summary: | 博士 === 國立成功大學 === 光電科學與工程研究所 === 95 === The main purpose of this dissertation is to study new fabrication processes and mechanism of carrier transport for organic optoelectronic devices. The investigations in this thesis include four parts: 1) study of polarized luminescence from organic material aligned by ion-beam-processed poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), 2) polymer light-emitting diodes with thermal inkjet printed PEDOT:PSS, 3) excimer laser irradiation induced suppression of off-state leakage current in organic thin-film transistors (OTFTs), and 4) controllable threshold voltage OTFTs by O2 plasma treatment on surface of polyurethane dielectrics. The brief descriptions of four parts are as follows,
(1) Study of polarized luminescence from organic material aligned by ion-beam-processed poly(3,4-ethylenedioxythiophene): polystyrenesulfonate
Currently organic light-emitting diodes (OLEDs) have attracted a lot of interests as a new display technology. In the first part, we prepare a polarized OLEDs based on 4,4’-Bis[2-9(-ethyl-3-carbazoyl)vinylenyl]-1,1’-biphenyl (BECVB), which emitted polarized blue light, aligned by ion-beam-processed and rubbing-processed hole- injecting/-transport poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer. A rubbing polyimide and photoalignment polyimide were also used to align BECVB. The dichroic ratios of linearly polarized photoluminescence of BECVB films aligning by various techniques were compared.
(2)Polymer light-emitting diodes with thermal inkjet printed PEDOT:PSS
In the second part, PEDOT:PSS films, prepared by inkjet-printing and spin-coating methods, have been studied using atomic force microscopy, micro-Raman spectroscopy, photoelectron spectroscopy, and four-point probe conductivity measurements. Electrical conductivity of the inkjet-printed film was enhanced by a factor of around 10 when compared to a spin-coating film. The improved conductivity was attributed to longer effective conjugation length of PEDOT chains in inkjet-printing PEDOT:PSS films as suggested by their micro-Raman spectroscopy. PEDOT:PSS films formed by the inkjet-printing method are appropriate for use as an anode for simplification of the fabrication process of polymer light-emitting diodes whose performance is about 1.2 cd/A.
(3)Excimer laser irradiation induced suppression of off-state leakage current in organic transistors
We report the suppression of the OFF-state leakage current and subthreshold swing (SS) in inkjet-printed poly(3-hexylthiophene) (P3HT) thin-film transistors with asymmetric work function source and drain electrodes. Indium-tin-oxide (ITO) material was used as source/drain electrodes and the source electrode was irradiated by KrF excimer laser. The dominant mechanisms for the suppressive IOFF could be attributed to the increase in the work function of ITO source irradiated by the excimer laser. Lower trap state density formed on the laser-irradiated source electrode. Holes could be easily injected into the channel at small lateral electric field resulting in smaller threshold voltage and SS.
(4)Adjust threshold voltage device by O2 plasma treatment on polyurethane modified dielectrics
Threshold voltage is one of the most important parameters for OTFTs. In the fourth part, we provide a new method to control the threshold voltage. A polyurethane (PU) films play the gate dielectric layers within OTFTs. The PU layer formed by spin coating and then the surface of PU treated under O2 plasma. Finally, organic polymer P3HT was inkjet-printed on the surface of PU to complete an OTFT. The threshold voltage of OTFTs increases with increasing the power of the O2 plasma. Additionally, the on-off ratio of OTFTs enhances three orders when the power of O2 plasma is above 500 W. Therefore, the method of O2 plasma treatment could effectively enhance the performance of OTFTs.
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