Papers by Keyword: Pentacene

Abstract: This work is devoted to the influence of magnetized water on dye extracted from Anchusa Italica plant and doped pentacene thin films. The findings resulted in optoelectronic behavior, showing that using magnetized water in the extraction process gives rise to distinct and superior characteristics as compared to using regular water. The Fourier-transform infrared method was used to analyze the structural properties of an Anchusa Italica-doped pentacene thin film. A comparative study on two samples was carried out: the first sample was affected by a static magnetic field and the other one was not. Optical properties including the absorption spectra absorption coefficient, optical energy gap, conventional and refractive factors were investigated by applying ultraviolet-visible spectroscopy ranging from 300 to 900 nm. The estimated band gap edge of the dye/doped pentacene affected with magnetization was reduced from 2.61 to 1.76 eV and converted into the recommended direct band gap to contribute to optical systems. The absorption spectra of the sample with magnetization effect appears to be more efficient than the one extracted using regular water. The power transmission coefficients (indirect to direct) were also affected because of the magnetic extraction procedure. The complex refractive index was used to study the magnetization effect on the resonance mode and transparent indicator. The absorption index was enhanced to 570 nm in the spectrum, whereas there was also a low attenuation coefficient. This is the first time that magnetized sol has been used in dye extraction processes.

Abstract: The dye-doped polymer is commonly used in the field of optoelectronics, given its effectiveness in optimising the device’s performance. This study is devoted to the synthesis and characterisation of Anchusa-Italica-doped Pentacene thin-film. Scanning electronic microscopy structural analysis, Fourier transform spectroscopy, and UV-visible transmittance spectra with a range of 300-900 nm were also carried out. The fundamental optical properties such as the absorption coefficient, optical energy gap, absorption and refractive indices were calculated based on the methods already used in the literature as Tauc’s relationship. The morphology of the samples indicated that dye structure was affected in the doped pentacene. The Fourier transform infrared technique (FT-IR) resulting spectrum of the doped samples also showed a significant absorption peak corresponding to C-H as an index of impurities. The calculated band-gap energy of the impurity sample was reduced and was the lowest compared to both the pure dye and polymer samples. The optical absorption and transmittance spectra revealed that it was positioned in the desirable ranges for optoelectronic applications. An anomaly in the absorption index was also observed through excitation of the resonance mode with transparent indication. This effect was deduced from the calculation of the refractive index. The results presented in this paper significantly contribute to the developments in the field of optoelectronic devices based on dye/polymer organic materials.

Abstract: For organic solar cells (OSC) such as dye-sensitized cell (DSSC) to compete with silicon-based cells in terms of stability, there is a need to further improve components which causes degradation. To answer the stability issue with liquid electrolyte, solid state dye-sensitized solar cell (SS-DSSC) was introduced. SS-DSSC promises performance consistency due to less power degradation compared to standard DSSC that uses liquid-based electrolyte. Pentacene (PEN), a semiconductor usually used on field-effect transistors is a material that has a higher hole and electron mobility when compared to amorphous silicon and also has a band gap suitable for solar energy conversion. In this study, PEN used as hole transporting layer in SS-DSSC was fabricated through spin coating and heating using a precursor and through vapour transport using powder. The PEN samples were then doped with bromine through different methods - immersion and vaporization. Characterization of the PEN samples through X-ray Diffraction, Energy Dispersive X-ray Fluorescence, and Atomic Force Microscopy reveal orthorhombic, thin film, and crystalline bulk phases present on different fabricated PEN samples as well as confirmed successful doping. Furthermore, the light harvesting parameters are analysed through SolarTM Light LS1000 Solar Simulator (AM 1.5, 100 mW/cm²) which confirm correlation between the increased efficiency, PEN layer growing methods, and bromine doping methods.

Abstract: The influence of contact thickness on electrical performance of bottom gate Organic Field Effect Transistor (BG-OFET) with staggered and planer structures is studied in this paper. Two dimensional device simulation is performed with identical dimensions for both devices which show a good agreement between simulated and measured results. Contact thickness is varied from 0nm to 20nm for planer and staggered structures. The electrical characteristics are strongly affected by the contact thickness variation. With increasing contact thickness, the threshold voltage shifts from negative to positive. The simulation results indicate that saturation current value of staggered structure is higher than that of planer. Although the current does not increase in staggered structure due to its increasing contact thickness, while the current in planer structure increases up to three times. However, current in planer is still below the current in staggered structure. The extracted field effect mobility and current on-off ratio at 20nm electrode thickness for staggered structure is 0.67 cm²/V.s and 10⁸, respectively. It has been observed that the field effect mobility, threshold voltage, sub-threshold slope, transconductance and current on-off ratio can be modified by varying contact thickness. Analysis of the results clearly demonstrates the significance of controlling the contact thickness in planer and staggered OFETs. It even offers a way to control OFETs parameters.

Abstract: For what is believed to be for the first time, the device physics based modeling approach to derive the generic model current equations of organic thin film transistor (OTFT) is described. Firstly, the current model equation is derived by considering the dependence of mobility on gate voltage and doping density, which is more realistic and relevant to organic materials containing TFTs. To model small molecule or polymer TFT, the potential drop across contacts is taken into account as contacts are not ohmic due to some morphological disorders. Further the effect of contact resistance is included and accordingly the generic model current equation is modified. It shows a good agreement of proposed current equation with simulated results which validates the proposed OTFT model from ohmic to saturation regime. Moreover, the analytical model is used to extract the contact and channel resistances in linear and saturation region and these resistances are verified through potential cut line (PCL) and transmission line methods (TLM). The extracted parameters are not only used to verify the electrical characteristics but also exhibit insight on contact potential, charge injection and transport phenomenon for organic TFT operation.

Abstract: The three photovoltaic cells with two different anode buffer layer on the basis of Pentacene/C60 as active layer was fabicated, the effect and mechanism of anode buffer layer on performance of organic photovoltaic cell are explored. The experimental result shows transition metal oxide inserted between organic active layer and ITO could increase short circuit current and open-circuit voltage,power conversion efficiency is increased to 107%,so it is effective anode buffer material.

Abstract: P-channel pentacene field effect transistorswith a Si/SiO₂/pentacene/Au structure were fabricated, and were gamma-ray irradiated with a Co⁶⁰ source. The changes of the drain current I_D vs. source/drain voltage V_SD (I_D - V_SD) characteristics were measured after every 200 Gy in silicon (Gy_Si) irradiations up to the total dose of 1200 Gy_Si. The drain current I_D continuously decreased to less than 10 % of that before irradiation after 1200 Gy_Si irradiation. The threshold voltage V_th continuously decreased up to 800 Gy_Si, started to saturate above 800 Gy_Si, and recovered above 1000 Gy_Si. The mobility m continued to decrease up to 1200 Gy_Si. Those behaviors were explained by accumulation of positive trapped charge within the gate insulator SiO₂ near the interface, continuous increase of interface traps near the interface between the SiO₂ and pentacene, and build up of electrons in the channel regions. These behaviors were discussed in comparisons with previously reported results on ultraviolet (UV) light irradiation experiments on similarly structured pentacene-based transistors.

Abstract: Electrical characterization of ⁶⁰Co γ-ray radiation effects on pentacene-based organic thin-film-transistors having two kinds of gate insulator have been carried out. For transistors with SiO₂ gate insulator, the threshold voltage shifts are consistent with positive charge trapping in the oxide and a “rebound” effect is observed. This “rebound” effect is attributed to the negatively charged interface traps generated during irradiation. For polyimide gate insulator, the threshold voltage continually decreases with an increasing total-dose. At total-dose of 1200 Gy (Si), for the SiO₂ gate insulator, the field-effect mobility decreased by almost 80%, and for polyimide gate insulator, it decreased by 40%.

Abstract: There is a current upsurge in research on devices with nanoparticles embedded in dielectrics. Such structures can operate as memories with high speed, high density, low voltage and low cost. Here, we report on hybrid gold nanoparticle-based metal-insulator-semiconductor (MIS) memory devices combining silicon technology and organic thin film deposition. The nanoparticles are deposited using a self-assembly technique at room temperature onto a 4.5 nm thermal silicon oxide layer. A 40 nm thin film of pentacene (deposited by flash thermal evaporation), polymethylmethacrylate (spin coated) and cadmium arachidate (deposited using the Langmuir- Blodgett technique) are used as insulators. Distinct capacitance-voltage (C-V) hysteresis is observed with a memory window that increases linearly with increasing voltage programming range. Clockwise and anticlockwise hysteresis in devices based on p-type and n-type silicon, respectively are observed, indicating that charges are injected from the top electrode to the nanoparticles rather than tunnelling through the thin SiO2 layer. However, thermal growth of SiO2 at a temperature below 800 °C resulted in a hysteresis in the opposite direction. The detailed electrical behaviour of the MIS devices will be discussed.

Abstract: We investigated the characteristics of pentacene thin films of different materials for gate insulators using atomic force microscope (AFM) and x-ray diffraction (XRD). The pentacene thin films are fabricated by evaporation on different polymer substrates. We used HMDS (Hexa Methyl Di Silazane), PVA (Poly Vinyl Alcohol) and PMMA (Poly Methyl Meth Acrylate) for the polymer substrates, on which pentacene is deposited at various substrate temperatures. The case of pentacene deposited on the PMMA has the largest grain size and least trap concentration. We also fabricated pentacene TFTs with the PMMA gate insulator. Pentacene TFTs with PMMA gate insulator, shows high field-effect mobility (ｕFET= 0.03 cm2/Vs) and large on/off current ratio (>105) and small threshold voltage (Vth= -6 V).