Fakhra Aziz

Influence of humidity conditions on the capacitive and resistive response of an Al/VOPc/Pt co-planar humidity sensor

The fabrication and characterization of a novel co-planar humidity sensor based on organic semiconducting material, vanadyl phthalocyanine (VOPc), is presented in this paper. Here we examine the effect of different humidity conditions on the capacitive and resistive response of VOPc thin films in the Al/VOPc/Pt co-planar structure. The two asymmetric electrodes, aluminum (Al) and platinum (Pt), were deposited through the photolithography technique. Thin films of VOPc were spun-cast on the glass substrate with primarily deposited asymmetric metal electrodes, from a solution of 30 mg ml−1 in chloroform at 3000 rpm. The gap between the electrodes was 17 µm. A 100-fold increase was observed in the capacitance of the VOPc sensing material with an elevation of relative humidity level. The resistance of the sensor reduced from 2.9 GΩ to 2.1 MΩ with increasing level of humidity. The VOPc thin film has been analyzed by x-ray diffraction as well as atomic force microscopy in order to get structural and morphological information on the sample. Adequate sensing properties such as enough sensitivity, good selectivity, linearity and reasonable response and recovery times have been obtained. The humidity-dependent properties of the sensor make it a good match for its potential application in commercial hygrometers.

Characterization of vanadyl phthalocyanine based surface-type capacitive humidity sensors

This study presents the fabrication and characterization of novel surface-type capacitive humidity sensors using vanadyl phthalocyanine (VOPc) as the active material. The devices, which comprise three different thicknesses, have been fabricated using the thermal evaporation technique. A thin film of VOPc is deposited on thoroughly cleaned glass substrates with pre-patterned Ag electrodes. The capacitive effect of the samples under humidity has been investigated. Comparison of the samples with different thicknesses shows that the thinnest device seems more sensitive towards humidity. The humidity dependent capacitance properties of the sensor make it beneficial for use in commercial hygrometers.

Investigation of Optical and Humidity-Sensing Properties of Vanadyl Phthalocyanine-Derivative Thin Films

In this study an active layer of Vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (VOPcPhO) has been employed in surface type humidity sensor. On top of preliminary deposited asymmetric metal electrodes, a VOPcPhO thin film was spun cast to obtain a surface type Al/VOPcPhO/Au sensor. The gap between the electrodes was 40 um. A solution of 30 mg/ml was deposited at 3000 rpm. The thickness of the VOPcPhO film was 150 nm. The capacitive effect of the sample was evaluated in the relative humidity range 0–87%RH, at room temperature. It was observed that the capacitance of the sensor increases 10 times under the effect of entire humidity range in the relative humidity level. The optical properties of VOPcPhO thin film were also investigated. The humidity-dependent capacitive properties make the sensor suitable for the application in the instruments used for environmental monitoring of humidity.

Eco-benign visible wavelength photodetector based on phthalocyanine-low bandgap copolymer composite blend

Herein, we demonstrate a novel solution-processed photodetector using an organic composite blend of VOPcPhO and PCDTBT to function as the donor (D) and the acceptor (A) materials, respectively. The absorption spectra of the composite blend have been successfully broadened to encompass almost the entire visible region by exploiting the spectral properties of PCDTBT moiety. The photodetector shows an efficient photo-current response as a function of varied illumination levels. Furthermore, current density–voltage (J–V) characteristics of the device, in the dark, have been employed to extract device parameters such as barrier height and rectification ratio. The conduction mechanisms at the electrode–semiconductor interface have also been investigated. As the proposed photodetector can harvest incident photons over almost the whole visible range, it can be potentially employed for practical applications.

Improvement in the photovoltaic properties of hybrid solar cells by incorporating a QD-composite in the hole transport layer

A hybrid solar cell (HSC) based on a ZnSe and CdSe QDs-composite with improved conversion efficiency has been demonstrated. A novel approach of incorporating a QDs-composite (CdSe and ZnSe QDs simultaneously), in the poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonate) (PEDOT : PSS) matrix by a simple cost effective solution processing technique, has been adopted. The combination of the QDs produced a 33% increase in the photo-conversion efficiency with a corresponding 67% enhancement in the fill factor (FF) when compared with the reference device. The micro-Raman analysis revealed effective strong coupling between both ZnSe and CdSe QDs, which promotes smooth charge transfer. This improved efficiency due to enhanced FF was achieved through interfacial engineering of the solution-processed hole transport layer, leading to facilitated charge transport and restrained bimolecular recombination. The present approach, outdoing the need of a cascaded layered structure, is compatible with the state-of-the-art hybrid solar cells, thus offering better throughput and a low cost manufacturing process for an improved-performance device.

ENHANCEMENT IN THE SENSING PROPERTIES OF METHYL ORANGE THIN FILM BY TiO2 NANOPARTICLES

This paper reports the enhancement in the sensing properties of organic dye methyl orange (MO) by introducing TiO2 nanoparticles. For this purpose, two surface type Ag/MO/Ag and Ag/MO:TiO2/Ag multifunctional sensors were fabricated by spin coating a 3.0 wt.% solution of MO and 3.0:0.3 wt.% of MO:TiO2 composite on pre-patterned silver (Ag) electrodes. The gap between Ag electrodes was 40 μm. The Ag/MO/Ag and Ag/MO:TiO2/Ag structures were characterized to investigate their response towards humidity and temperature variations. The Ag/MO:TiO2/Ag sensor exhibited better sensitivity and response time than Ag/MO/Ag sensor. The large surface to volume ratio of TiO2 nanoparticles is the primary reason for the higher sensitivity of Ag/MO:TiO2/Ag sensor. The sensors can be used to detect humidity variations from 30% to 95% RH and temperature variation from 30°C to 200°C with good stability. Surface morphologies of the film were investigated by scanning electron microscope (SEM).

Photovoltaic effect in single-junction organic solar cell fabricated using vanadyl phthalocyanine soluble derivative

Purpose – The purpose of this paper is to study the optical and electrical characteristics of a single-junction solar cell based on a green-colour dye vanadyl 2,9,16, 23-tetraphenoxy-29H, 31H-phthalocyanine (VOPcPhO). The use of soluble vanadyl phthalocyanine derivative makes it very attractive for photovoltaic applications due to its tunable properties and high solubility. Design/methodology/approach – A photoactive layer of VOPcPhO has been sandwiched between indium tin oxide (ITO) and aluminium (Al) electrodes to produce a ITO/PEDOT:PSS/VOPcPhO/Al photovoltaic device. The VOPcPhO thin film is deposited by a simple spin coating technique. To obtain the optimal thickness for the solar cell device, different thicknesses of the photoactive layer, achieved by manipulating the spin rate, have been investigated. Findings – The device exhibited photovoltaic effect with the values of Jsc, Voc and FF equal to 5.26 × 10-6 A/cm2, 0.621 V and 0.33, respectively. The electronic parameters of the cell have been obtai...

Compositional engineering of VOPcPhO-TiO2 nano-composite to reduce the absolute threshold value of humidity sensors

This research work demonstrates compositional engineering of an organic-inorganic hybrid nano-composites for modifying absolute threshold of humidity sensors. Vanadyl-2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (VOPcPhO), an organic semiconductor, doped with Titanium-dioxide nanoparticles (TiO2 NPs) has been employed to fabricate humidity sensors. The morphology of the VOPcPhO:TiO2 nano-composite films has been analyzed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The sensors have been examined over a wide range of relative humidity i.e. 20-99% RH. The sensor with TiO2 (90nm) shows reduced sensitivity-threshold and improved linearity. The VOPcPhO:TiO2 (90nm) nano-composite film is comprised of uniformly distributed voids which makes the surface more favorable for adsorption of moisture content from environment. The VOPcPhO:TiO2 nano-composite based sensor demonstrates remarkable improvement in the sensing parameter when equated with VOPcPhO sensors.

Enhancement of electrical properties of vanadyl phthalocyanine derivative by PCBM

Purpose – The purpose of this paper is to investigate the effect of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) on improvement of physical and electrical properties of vanadyl phthalocyanine derivative. The correlation between the physical characteristics of the active layers, comprising vanadyl 2,9,16, 23-tetraphenoxy-29H,31H-phthalocyanine (VOPcPhO) and PCBM, and the electrical properties of metal/organic/metal devices have been studied. The use of soluble vanadyl phthalocyanine derivative makes it very attractive for a variety of applications due to its tunable properties and high solubility. Design/methodology/approach – The sandwich type structures Al/VOPcPhO/Al and Al/VOPcPhO:PCBM/Al were fabricated by spin casting the active organic layers between the top and bottom (aluminum) electrodes. The stand-alone (VOPcPhO) and composite (VOPcPhO:PCBM) thin films were characterized by X-ray diffraction, atomic force microscopy, UV/Vis and Raman spectroscopy. The electronic properties of the metal/organ...

Employment of single-diode model to elucidate the variations in photovoltaic parameters under different electrical and thermal conditions

In this research work, numerical simulations are performed to correlate the photovoltaic parameters with various internal and external factors influencing the performance of solar cells. Single-diode modeling approach is utilized for this purpose and theoretical investigations are compared with the reported experimental evidences for organic and inorganic solar cells at various electrical and thermal conditions. Electrical parameters include parasitic resistances (Rs and Rp) and ideality factor (n), while thermal parameters can be defined by the cells temperature (T). A comprehensive analysis concerning broad spectral variations in the short circuit current (Isc), open circuit voltage (Voc), fill factor (FF) and efficiency (η) is presented and discussed. It was generally concluded that there exists a good agreement between the simulated results and experimental findings. Nevertheless, the controversial consequence of temperature impact on the performance of organic solar cells necessitates the development of a complementary model which is capable of well simulating the temperature impact on these devices performance.