Roberto Koji Onmori

An electrical study of a thin film poly(o-methoxyaniline) field effect transitor

A field-effect transistor (FET) having poly(o-methoxyaniline) (POMA) as the active layer was built on a SiO 2 -Si substrate which acts as the gate. The POMA layer was deposited by spin coating on the substrate interdigitated with gold lines and which acts either as the source or drain contact. A tentative theoretical model based on the Schottky gold/polymer interface contact and on the electronic properties of the POMA film was developed to explain the characteristic behavior of the FET device.

Influência de diferentes solventes utilizados na deposição de filme de poli(9-vinilcarbazol) em dispositivos OLEDs

This work studies the influence of the film deposition process on light emission performance and on threshold voltage of OLEDs, with architecture glass/ITO/PEDOT:PSS/PVK/Alq3/Al. The commercial PVK was dissolved in different solvents such as: chloroform, tetrahydrofuran, 1,2,4-trichlorobenzene and trimethylpentane. OLEDs were characterized by current-voltage and revealed a significant influence of the solvents, although all devices emitted green electroluminescence. A difference in threshold voltage up to 10 V was observed among OLEDs prepared from different solvents. The 1,2,4-trichlorobenzene showed best performance, presenting lowest treshold voltage (≈ 6 V), followed by tetrahydrofuran (≈ 8 V), trimethylpentane (≈ 14 V) and chloroform (≈ 16 V).

Reversible photovoltaic/electroluminescent effects of Al/MH-PPV/ITO structures

Schottky diode structures employing chlorine doped MH-PPV (Methoxy-Hexiloxy-P-Phenylene-Vinylene) as active layers were prepared to study the electronic possibilities of this conjugated polymer. MH-PPV films were deposited by spin-coating technique on ITO (indium tin oxide) coated glass substrates. Aluminum contact was then vacuum evaporated. Dark conductivity characteristic is that of a rectifier diode. Upon illumination the device shows photovoltaic characteristics. When a voltage is applied, however, the structure shows electroluminescence with a peak at 606nm. In this sense, it is a reversible photonic device.

Study of heterojunction diodes using POMA/PANI and amorphous/microcrystalline silicon structures

Photovoltaic diode based on a heterojunction structure combine on amorphous and microcrystalline silicon, deposited by PECVD process, with polyaniline- (PANI) and poly(o-methoxyaniline)-(POMA), using PIN structures. We report IxV characteristic curves of glass/ITO/a-Si:H(p)/POMA or PANI/μc-Si:H(n)/Al structures. Preliminary results show a dependence of the IxV curves on the polymer doping level. This structure shows an insulating behavior for undoping or very low doping, photovoltaic effect at medium doping and a typical resistance curve at high doping level. The device is a promising tool to understand transport and electronic properties of the polymers.

Photovoltaic effect on μc-Si:H(n+)/poly(o-methoxyaniline)/a-Si:H(p) structures

Abstract Heterostructures, having poly(o-methoxyaniline) (POMA) deposited by spin coating process as active layer, were built with n -type microcrystalline silicon and p -type amorphous silicon deposited by CVD process near room temperature. J x F device characteristic curves showed rectification properties whose current enhances under visible light illumination. This photomechanism may act directly in the bulk polymer, generating photocarriers, or in the p -Si/POMA interface injecting positive carriers from Si into the POMA bulk. Photovoltage phenomenon was also observed, indicating the possibility of fabricating photovoltaic solar cells with POMA films.

Study of a POMA based solar cell

A new type of solar cell based on poly(o-methoxyanilinc)-POMA as active layer is proposed. A simple Schottky structure was prepared: Al/POMA/ITO/glass. The POMA layer was deposited by the casting method and doped with aqueous hydrochloric acid solutions. Light absorption in POMA produces carriers for the electrical current. The dark current vs. voltage curves show a rectification feature. Under illumination, the short circuit current increases with the light intensity, characteristic of the photovoltaic effect. Studies of the dependence on hydrochloric acid concentration, doping time and POMA layer thickness were done. The easy synthesis of POMA and the simplicity of this device arc the important aspects of this structure.

Low cost UV-Ozone reactor mounted for treatment of electrode anodes used in P-OLEDs devices

Low cost UV-Ozone reactor using a high pressure mercury vapor lamp of 80 watts without outer bulb showed good results for treatment of ITO films used as anode electrode in the assembly of P-OLED (polymer-organic light emitting diode) devices. This study revealed 20 minutes as effective treatment time and it was verified also that the effect of UV-Ozone treatment loses its efficiency as the elapsed time increases. It was analyzed with measurements of contact angle using a droplet of PEDOT:PSS polymer. P-OLEDs devices were mounted with architecture: ITO/PEDOT:PSS/PVK/Alq3/Al. The PVK polymer was diluted in organic solvent of 1,2,4-trichlorobenzene with concentrations of: 5, 10, 20 and 30 mg/mL. Results revealed better performance of P-OLED devices for concentration of 5 mg/mL resulting in lower threshold voltage, elevation of electrical current and similar diode curve.

Transistor por efeito de campo e fotocondutor de poli(o-metoxianilina).

ABSTRACT: A field effect transistor - FET made from poly(o-methoxyaniline) (POMA), which is a conductive polymer, was developed. Several modifications were carried out to adapt the procedures generally used in traditional device developments. The characteristic of the FET produced was sensible to the gate modulation, but it operates even for VG = 0. The drain current ID enhanced under visible and near infrared radiation, showing the photoconductor character of POMA and, consequently, of the device. A theoretical model, based on the electronic properties of POMA and on the metal-polymer interface, was developed which is in good agreement with the experimental results.

Low cost spinner developed for deposition of thin films used in OLED devices

This work aims the development of a compact spinner to be used inside the glove-box chamber to deposition of polymeric thin films used in the build of OLED devices. Initially, ten fans extracted of microcomputers were tested with commercial multi-voltage power supply. Four fans were selected based on the standard deviation of speed. A variable power supply was also built in order to get a more detailed response in terms of electrical current and speed in function of applied voltage. The fan that showed less variation of speed with applied voltage was selected for deposition tests using polymeric photoresist solution on the ITO (indium tin oxide) coated glass. This polymer was deposited by spin-coating at different speeds: 1000, 2000, 3000 and 4000 rpm and dried for the thicknesses measurement revealing good uniformity. Finally, three OLED devices were assembled with 2000 and 3000 rpm and the layers were dried under the same conditions. In the structure of the devices were used the materials deposited layer-by-layer:glass/ITO/PEDOT:PSS/ Polyfluorene (PFpf)/Al. The OLED devices revealed blue light electroluminescence. The I-V curves showed better performance for OLED devices mounted at 2000 rpm with higher current density and similar appearance to the diode curve.