Showing papers by "Muhammad Hassan Sayyad published in 2011"

Electrical characterization of the organic semiconductor Ag/CuPc/Au Schottky diode

Abstract: This paper reports on the fabrication and investigation of a surface-type organic semiconductor copper phthalocyanine (CuPc) based diode. A thin film of CuPc of thickness 100 nm was thermally sublimed onto a glass substrate with preliminary deposited metallic electrodes to form a surface-type Ag/CuPc/Au Schottky diode. The current-voltage characteristics were measured at room temperature under dark conditions. The barrier height was calculated as 1.05 eV The values of mobility and conductivity was found to be 1.74 × 10−9 cm2 (V · s) and 5.5 × 10−6 Ω−1 · cm−1, respectively. At low voltages the device showed ohmic conduction and the space charge limited current conduction mechanisms were dominated at higher voltages.

Potential of 5,10,15,20-Tetrakis(3′,5′-di-tertbutylphenyl)porphyrinatocopper(II) for a multifunctional sensor

Abstract: An organic compound 5,10,15,20-Tetrakis(3′,5′-di-tertbutylphenyl)porphyrinatocopper(II) (TDTPPCu) is synthesized and studied as an active material for multifunctional capacitive sensor. The capacitance of the device as a function of illumination, humidity and temperature has been investigated. It is observed that the capacitance increases by 4.7 times from the dark condition under an illumination of 3850 lx. The capacitance is also changed 9.5 times with the increase in relative humidity (RH) from 30% to 95%. No change in capacitance appeared below critical temperature 120 °C. Based on the experimental results for the multifunctional sensor a mathematical model has been developed. The model is mainly based on the assumption that the capacitive response of the sensor is associated with dielectric polarization. The sensors are simulated using this model. The simulated results match well with experimental results.

Investigation of temperature-dependent electrical properties of p-VOPc/n-si heterojunction under dark conditions

Abstract: An organic/inorganic heterojunction p-VOPc/n-Si was fabricated and its electrical properties were investigated. Temperature-dependent dark current–voltage (I–V) characteristics of the heterojunction exhibited rectification behaviour with a rectification ratio of 405 at ±1 V and room temperature. The current–voltage characteristics of the cell showed ohmic conduction at low voltages followed by a space charge-limited current (SCLC) conduction dominated by an exponential trap distribution at higher voltages. At room temperature, the series and shunt resistances were found to be approximately 1.4 and 100 kΩ, respectively. Diode ideality factor n was found to be 3.2 at room temperature and dropped to 1.9 at 363 K. Room temperature mobility of vanadyl phthalocyanine (VOPc) was extracted from the I–V characteristics in the SCLC region and was found approximately 15.5 × 10−3 cm2 V−1 s−1. The effective barrier height, ФB, was estimated as 0.77 eV. The effect of temperature, on various heterojunction parameters was recorded under dark conditions and at temperatures ranging from 300 to 363 K.

Direct current and impedance spectroscopic studies on MoO3 modified ZnPc/ITO Schottky diodes

Abstract: We use experimental results of direct current and low signal impedance spectroscopy to investigate the conduction mechanism in organic semiconductor ZnPc. The experimental results demonstrate an increase in current and holes mobility by the introduction of a thin MoO3 film at the ITO/ZnPc interface. This significantly improves the device performance. The improvement is explained in terms of the reduction in the effective barrier for charge transfer from ZnPc to ITO.

Impedance spectroscopic studies of an organic semiconductor device incorporating a thin film of highly doped ZnPc with MoO3

Abstract: We use experimental results of low signal impedance spectroscopy to investigate the conduction mechanism in organic semiconductor, zinc phthalocyanine (ZnPc). The first 10 nm, of a total of 150 nm thermally deposited ZnPc, was doped with molybdenum oxide (MoO 3 ) by co-evaporation to obtain a 20% doping concentration. The ac electrical parameters were measured at room temperature in the dc bias and frequency ranges of 0–5 V and 100 Hz–0.1 MHz, respectively. The variation of bulk resistance with applied bias presents a clear indication of space charge limited conduction in the fabricated device. The experimental results show a strong frequency dependence of capacitance and loss tangent at low frequencies and high applied bias, while at higher frequencies and low applied bias a weak dependence is observed. Moreover, the ac conductivity shows a strong dependence on frequency and is found to vary as ω s with the index s ≤1.15 suggesting a dominant hopping mechanism of conduction.

Production and characterization of nanoparticle dispersions of organic semiconductors for potential applications in organic electronics

Abstract: The technique of pulsed laser ablation in a liquid has been applied to the synthesis of the nanoparticles dispersion of an organic semiconductor cobalt phthalocyanine (CoPc). A pellet of CoPc, placed in the bottom of a glass beaker filled with deionized water, was irradiated with a nanosecond Nd:YAG laser working at 532 nm and a colloidal solution of the nanoparticles of CoPc was obtained. To test the potentiality of this nanodispersion for the fabrication of low cost organic electronic devices, a surface-type Ag/NanoCoPc/Ag humidity sensor was fabricated and effect of humidity on the capacitance of the sensor was studied for 0–90% RH. In the 0–55% RH range no change in the capacitance of the sensor was observed but above 55% RH a significant increase in the capacitance with the increase in humidity was observed. The observed humidity-capacitance relationship is explained on the basis of water adsorption and dielectric physics theory. The response-and recovery-times of the sensor were measured as less than 5 s.

Investigation of Temperature-Dependent Electrical Properties of Tc-CuPc: PCBM Bulk Heterojunction (BHJ) under Dark Conditions

Abstract: An organic bulk heterojunction (BHJ) was fabricated using a blended film containing Copper (II) tetrakis(4 cumylphenoxy)phthalocyanine (Tc CuPc) along with (6,6) Phenyl C61 butyric acid methyl ester (PCBM). Weight ratio between Tc CuPc and PCBM was 1:1. The electrical properties of Tc CuPc:PCBM BHJ were examined. Rectifying nature of the BHJ was displayed by current voltage (IV ) curves, recorded in dark and at various temperatures. At low voltages, conduction was ohmic succeeded by space charge limiting current (SCLC) conduction at higher voltages in which exponential trap distribution was dominant. Series resistance, shunt resistance, ideality factor, effective barrier height and mobility at room temperature were found to be 526 4, 482 k4, 3.7, 0.17 eV and 2×10 7 cm 2 V 1 s 1 respectively. Temperature effect towards different BHJ parameters was observed under dark condition.

Investigation of 5,10,15,20-Tetrakis(3-,5--Di-Tert-Butylphenyl)Porphyrinatocopper(II) for Electronics Applications

Abstract: In this work, an organic compound 5,10,15,20Tetrakis(3,5-di-tertbutylphenyl)porphyrinatocopper(II) (TDTBPPCu) is studied as an active material for thin film electronic devices. To investigate the electrical properties of TDTBPPCu, junction of TDTBPPCu with heavily doped n-Si and Al is fabricated. TDTBPPCu film was sandwiched between Al and n-Si electrodes. Various electrical parameters of TDTBPPCu are determined. The current-voltage characteristics of the junction are nonlinear, asymmetric and show rectification behavior, which gives the clue of formation of depletion region. This behavior indicates the potential of TDTBPPCu for electronics applications. The current-voltage and capacitance-voltage techniques are used to find the different electronic parameters. Keywords—P-type, organic semiconductor, Electrical characteristics

Optoelectronic Properties of Vanadyl phthalocyanine Based Organic-Inorganic Hybrid Devices

Abstract: The Optoelectronic properties of organic-inorganic hybrid devices consisting of Ag/VOPc/n-Si/Ag structure have been investigated through analyzing the current-voltage characteristics. We have also studied the effect of illumination on the open circuit voltage, capacitance and reverse resistance with consideration of VOPc film thickness. The dark I-V characteristics display rectification behaviour of such hybrid structures and a very high photo-capacitive response under illumination of 200 lx is observed. Furthermore due to the generation of photo induced charges, under illumination, the decrease in reverse bias resistance to one third of its value is observed.

Application of Formyl-TIPPCu (II) for Temperature and Light Sensing

Abstract: Effect of temperature and light was investigated on a thin film of organic semiconductor formyl-TIPPCu(II) deposited on a glass substrate with preliminary evaporated gold electrodes. The electrical capacitance and resistance of the fabricated device were evaluated under the effect of temperature and light. The relative capacitance of the fabricated sensor increased by 4.3 times by rising temperature from 27 to 187C, while under illumination up to 25000 lx, the capacitance of the Au/formyl-TIPPCu(II)/Au photo capacitive sensor increased continuously by 13.2 times as compared to dark conditions. Keywords—formyl-TIPPCu(II), Organic semiconductor, Photocapacitance, Polarizability.