Papers by Keyword: Organic Semiconductor

Abstract: Organic optoelectronic devices such as light-emitting diodes and solar cells present unique challenges for surface cleaning and preparation because of their large area and the ‘soft’, thin film nature of the materials involved. This paper gives an introduction to this class of semiconductor devices and covers a recent example of how surface cleaning impacts the long-term reliability of organic light-emitting diodes being commercialized for solid-state lighting.

Abstract: The optical absorption spectrum, Photoluminesces, and non-linear optical properties for Copper Phthalocyanine (CuPc) thin films (150,300 and 450 nm) respectively have been investigated via pulsed laser deposition technique. The absorption spectrum indicted that there are two bands one in UV around 330 nm which called B-band and the second in Visible around 650nm which called Q-band. Photoluminescence spectrum related to deposit samples has been determined with different thicknesses. From closed and open aperture Z-scan data non-linear absorption coefficient and non-linear refractive index have been calculated respectively using He-Ne laser which have beam waist of (24.2 μm), wave-length of (632.8 nm) and Rayleigh thickness was 2.9 mm. Through dividing closed by open apertures, non-linear refractive index was calculated accurately. Finally, the study also showed the suitability of the deposited films as an optical limiter at the wavelength 632.8 nm.

Abstract: Organic devices are advantageous in term of high carrier mobility, lightweight and flexibility. The solution processed method offers economic and efficient device fabrication in small laboratory scale. The α-quaterthiophene (α-4T) is an oligomer and a p-type organic semiconductor. In this study, pure α-4T and polylactide acid (PLA)/α-4T films were spin-coated on glass and indium tin oxide (ITO) substrates at low spin frequency. The hydrated films were left to dry at room temperature and later in vacuum oven. The α-4T microstructures changed when blended with the polymer. The roughness of the 180 nm ITO film was found to be 1 - 30 nm and the organic layer formed uneven thickness (max ~ 300 nm) thicker toward the edge. The preparation of spin coated organic thin film is the first step towards realizing solution processed organic device in electronic packaging.

Abstract:

Dip-coating is a conventional solution processing technology to prepare large-area films at a low cost and with cheap facilities. For semiconductor film processing, crystal orientation and thickness uniformity are the primary factors that determine the film quality and its electrical performance. These requirements are readily satisfied with the dip-coating method because the film morphology can be effectively optimized by tuning the withdrawal speed. This work optimizes the withdrawal speed for the dip-coating of patterned semiconductor films of 400×500 mm² as well as that for film dip-coating on the whole surfaces of the substrate. For both experiment, optimized electrical mobility is achieved at the same withdrawal speed, however, the random crystal orientation of the patterned films causes a remarkable decrease in device performance.

Abstract: By using organic semiconductor CuPc as photosensitive materials, we prepared an organic thin film transistor with the vertical structure consisted of metal Cu/ organic semiconductor CuPc/ Al/ organic semiconductor CuPc/ indium tin oxide ITO. CuPc semiconductor material has good photosensitive properties in the 700 nm light. When the light signal irradiates organic semiconductor photosensitive material, the electron-hole exciton is separated into photocurrent in built-in electric field produced by organic semiconductor material/ metal schottky contact. It transforms into the driving current of organic photoelectric triode. By using its current amplification effect, the output current increase obviously. The test result shows that the I-V characteristics of the transistor are obvious unsaturated triode characteristics. When using 700 nm light to irradiate the device, the working current of the device increases obviously.

Abstract: Materials with both electrical and magnetic properties are required for various applications ranging from electric and magnetic shields, molecular electronics, and sensors to microwave absorbers. Conducting polymers with the addition of magnetic oxides composites are suitable for such uses. Such is the case of the polyaniline (PANI), an organic polymer, mixed with magnetite. We have prepared through a new chemical method a PANI/ Fe₃O₄ composite with different amount of magnetic oxide from 0.3% m/m on the composite up to 42% m/m. The final product is a powder with good solubility in some organic solvents as chloroform. Structural morphological studies, transport properties (the electrical conductivity as a function of temperature) and magnetic characterization were performed on the oxides, on PANI and on the composites. We have explored the answer of these composites as absorbers in the microwave region to determine its potential technological application. An interesting magnetoresistance (MR) behavior was observed. The results are related to the particle size and to the influence of the percentage of oxide in the composite.

Abstract: In this paper, a thin layer of perylene tetracarboxylic bisbenzimidazole (PTCBI) is investigated as a potential hole-blocking contact in an a-Se photodetector. The behavior of the device was characterized as a function of electric field under light and dark conditions. It was found that the PTCBI layer permits operation at high electric fields (>>10 V/μm) while maintaining a dark current density below 200 pA/mm². Short pulse experiments were performed to assure that charge accumulation at the organic/a-Se interface is negligible and does not reduce the electric field in the a-Se layer. The detector investigated uses a simple low temperature fabrication process based on widely available semiconductor materials that can be easily integrated into current large area digital imager manufacturing processes.

Abstract: Organic semiconductor-based solar photovoltaic cells and sensors are scalable, printable, solution processable, bendable and light-weight. Furthermore, organic semiconductors require low energy fabrication process, hence can be fabricated at low cost as light-weight solar cells and sensors, coupled with the ease of processing, as well as compatibility, with flexible substrates. Organic semiconductors have been identified as a fascinating class of novel semiconductors that have the electrical and optical properties of metals and semiconductors. The continuous demand to improve the properties of organic semiconductors raises the quest for a deep understanding of fundamental issues and relevant electronic processes. Organic semiconductor thin film is sandwiched between two metal electrodes of indium tin oxide (ITO) and aluminum to form organic photovoltaic solar cell. Several types of organic semiconductors have been utilized as the photoactive layer in the solution processable organic solar cells. The performance of the fabricated solar cells can be improved by dissolving the material in the right choice of solvent, annealing of organic thin film, slowly forming the thin film and introducing an infra-red absorbance layer. Besides, organic semiconductor-based sensors can be fabricated utilizing either in a sandwidch type or planar type device. Some of these techniques and the experimental results are presented.

Abstract: Hybrid photovoltaic concepts based on a nanoscale combination of organic and inorganic semiconductors are promising way to enhance the cost efficiency of solar cells through a better use of the solar spectrum, a higher ratio of interface-to-volume, and the flexible processability of polymers. In this work, two types of thin film solar cells have been developed. In both types of solar cells, poly-N-vinylcarbazole (PVK) is used as electron donor, cadmium sulfide (CdS) and titanium dioxide (TiO2) nanocrystals are used as electron acceptors, respectively. Since TiO2 has a wide band gap and can only absorb UV light, in the second type of solar cell, ruthenium dye is used as photo-sensitizer. The preliminary results of photoconductive and photovoltaic characteristics of these two inorganic-organic composites are presented.

Abstract: The electronic properties of organic field effect transistors limit the efficiency of integrated circuits build on basis of printed organic semiconductors. In order to control the mobility of high efficient semiconductors, like rubrene, tetracene, tetracyanoquinodimethane (TCNQ), copper phthalocyanine and many others, single-crystal field-effect transistors have been prepared on surfaces of single crystals and characteristics have been measured. The highest mobility has been measured on rubrene single crystals. The mobility of as-grown crystals measured by air-gap field effect transistor is in the range of 10 cm²/Vs but falls below 1 cm²/Vs during reduction. It was observed that the measured mobility depends on the dielectric used for field effect transistors.