Khasan S. Karimov

A Humidity Sensing Organic-Inorganic Composite for Environmental Monitoring

In this paper, we present the effect of varying humidity levels on the electrical parameters and the multi frequency response of the electrical parameters of an organic-inorganic composite (PEPC+NiPc+Cu2O)-based humidity sensor. Silver thin films (thickness ∼200 nm) were primarily deposited on plasma cleaned glass substrates by the physical vapor deposition (PVD) technique. A pair of rectangular silver electrodes was formed by patterning silver film through standard optical lithography technique. An active layer of organic-inorganic composite for humidity sensing was later spun coated to cover the separation between the silver electrodes. The electrical characterization of the sensor was performed as a function of relative humidity levels and frequency of the AC input signal. The sensor showed reversible changes in its capacitance with variations in humidity level. The maximum sensitivity ∼31.6 pF/%RH at 100 Hz in capacitive mode of operation has been attained. The aim of this study was to increase the sensitivity of the previously reported humidity sensors using PEPC and NiPc, which has been successfully achieved.

Effects of Temperature and Humidity on Electrical Properties of Organic Semiconductor Orange Dye Films Deposited from Solution

In this study the effects of temperature and humidity on electrical properties of organic semiconductor orange dye (OD) have been examined. Thin films of OD were deposited from 10 wt.% aqueous solution on Au and SnO2 substrates at room temperature under normal gravity conditions, i.e., 1 g and also by using a spin coater at an angular speed of 1000 RPM. Two different types of structures: surface OD/Au and sandwich Al/OD/SnO2, Al/OD/Au were fabricated and their DC and low frequency AC characteristics were evaluated for the temperature range 30–70°C at ambient humidity of 50–80%. It was observed that the Schottky characteristics exhibited by these devices are temperature and humidity dependent. It was further observed that devices with Al electrodes act as a primary battery and the zero biased current (Izo) increases by increasing the device temperature which is explained on the basis of temperature assisted electrochemical reaction due to the correction of Al electrode. It was found that certain sandwich structures are more sensitive to humidity than others and the observed resistance to humidity ratio for OD/Au was 5.4 whereas for Ga/OD/Au samples it was 5.0.

Surface-type nonvolatile electric memory elements based on organic-on-organic CuPc-H2Pc heterojunction*

A novel surface-type nonvolatile electric memory elements based on organic semiconductors CuPc and H2Pc are fabricated by vacuum deposition of the CuPc and H2Pc films on preliminary deposited metallic (Ag and Cu) electrodes. The gap between Ag and Cu electrodes is 30–40 μm. For the current–voltage (I–V) characteristics the memory effect, switching effect, and negative differential resistance regions are observed. The switching mechanism is attributed to the electric-field-induced charge transfer. As a result the device switches from a low to a high-conductivity state and then back to a low conductivity state if the opposite polarity voltage is applied. The ratio of resistance at the high resistance state to that at the low resistance state is equal to 120–150. Under the switching condition, the electric current increases ~ 80–100 times. A comparison between the forward and reverse I–V characteristics shows the presence of rectifying behavior.

Effective management of combined renewable energy resources in Tajikistan.

Water is needed mostly in summer time for irrigation and in winter time for generation of electric power. This results in conflicts between downstream countries that utilize water mostly for irrigation and those upstream countries, which use water for generation of electric power. At present Uzbekistan is blocking railway connection that is going to Tajikistan to interfere to transportation of the equipment and materials for construction of Rogun hydropower plant. In order to avoid conflicts between Tajikistan and Uzbekistan a number of measures for the utilization of water resources of the trans-boundary Rivers Amu-Darya and Sir-Darya are discussed. In addition, utilization of water with the supplement of wind and solar energy projects for proper and efficient management of water resources in Central Asia; export-import exchanges of electric energy in summer and winter time between neighboring countries; development of small hydropower project, modern irrigation system in main water consuming countries and large water reservoir hydropower projects for control of water resources for hydropower and irrigation are also discussed. It is also concluded that an effective management of water resources can be achieved by signing Water treaty between upstream and downstream countries, first of all between Tajikistan and Uzbekistan. In this paper management of water as renewable energy resource in Tajikistan and Central Asian Republics are presented.

Thermo photo-electrochemical effect in n-InP/aqueous solution of orange dye/C cell

The effect of light and heat is studied on the electrical properties of an electrochemical n-InP/aqueous solution of orange dye/C cell. The cell is investigated under the light and heat of filament bulb. The n-type indium phosphide and carbon plates are used as electrodes. The aqueous solution of organic material orange dye (C17H17N5O2) in distilled water is served as electrolyte at 1, 3 and 5 wt. % concentration. The cell is assembled in sealed organic glass box with dimensions 35 × 13 × 14 mm. The open circuit voltage (Voc) and short circuit current (Isc) of the cell are observed by illuminating and heating the samples. The temperature is raised up to 60°C from 25°C when light intensity is increased from dark condition to 425 W/m2. It is observed that the relationship between light intensity and temperature is approximately linear for all cases. The Voc and Isc increase 100% and 300% respectively by increasing the light. The reported n-InP/aqueous solution of orange dye/C cell can be considered as small converter of light and heat into electric power.

CuPc/C60 heterojunction thin film optoelectronic devices

The optoelectronic properties of heterojunction thin film devices with ITO/CuPc/C60/Al structure have been investigated by analyzing their current–voltage characteristics, optical absorption and photocurrent. In this organic photovoltaic device, CuPc acts as an optically active layer, C60 as an electron-transporting layer and ITO and Al as electrodes. It is observed that, under illumination, excitons are formed, which subsequently drift towards the interface with C60, where an internal electric field is present. The excitons that reach the interface are subsequently dissociated into free charge carriers due to the electric field present at the interface. The experimental results show that in this device the total current density is a function of injected carriers at the electrode–organic semiconductor surface, the leakage current through the organic layer and collected photogenerated current that results from the effective dissociation of excitons.

Resistance Pressure Sensor Based on Ag/Cu2O-PEPC-NiPc/Al Composite

This work reports on the fabrication and investigation of pressure sensor based on Ag/Cu2O-PEPC-NiPc/Al composite. The active layer of the composite was deposited by drop-casting of the blend Cu2O-PEPC-NiPc on flexible substrate. The thin film of the blend consist of cuprous oxide (Cu2O) micropowder, (5 wt. %), poly-N-epoxypropylcarbazole (PEPC), (2 wt. %) and nickel phthalocyanine (NiPc) micropowder, (3 wt. %) in benzol (1 ml). The film thickness of the composite is in the range of 20-30 μm. It is found that the fabricated sensor is sensitive to pressure and showed good repeatability. The decrease in resistance of the sensor is observed 10 times by increasing the external uniaxial pressure up to 11.7 kNm-2. The experimentally obtained results are compared with the simulated results and showed reasonable agreement with each other.

Effect of humidity on copper phthalocyanine films deposited at different gravity conditions

Purpose The paper aims to study the effects of humidity on the electrical properties of copper phthalocyanine (CuPc) thin films deposited at different gravity conditions. Design/methodology/approach Surface-type samples were fabricated on glass substrates with preliminary-deposited copper electrodes. The CuPc solution was prepared in benzene. The thin films of CuPc were deposited on these substrates at diverse gravity conditions by drop-casting and centrifugation at 1 × g and 70 × g, respectively. Impedance and capacitance of the fabricated devices were measured against the different relative humidity ranging from 32 to 98 per cent. Findings The impedance and the capacitance of the CuPc film were found to be dependent on the ambient humidity levels (32-98 per cent) and the gravity conditions (1 × g and 70 × g) opted during the fabrication process. Research limitations/implications The centrifugation technique can potentially be used in the instrumentation industry for the fabrication of humidity sensors. Practical implications The results of the investigations can potentially be used in the instrumentation and optoelectronics industry for the fabrication of humidity sensors. Originality/value CuPc films were deposited from a solution in benzene using drop-casting and centrifugation. The electrical properties of the films were found to be dependent on film fabrication conditions and ambient humidity levels. Growth-dependent electrical properties of the CuPc films can be explained by considering their structure.

Space Charge–Limited Current Model for Polymers

7 Polymers have exceptional charge transport mechanism as a combination of delocali‐ 8 zation and localization of charge carriers with intramolecular and intermolecular charge 9 interaction, respectively, and most of the time, it is interpreted with Mott‐Gurney space 10 charge–limited current model. As polymers are full of traps, therefore, Mott‐Gurney 11 space charge–limited model is modified with various trap distributions as trapped space 12 charge–limited model. The most crucial parameter affected by the nature and distribu‐ 13 tion of traps is the carrier mobility, and it is argued that space charge–limited model is 14 an acceptable choice for the mobility measurement for polymer. Similarly, in order to 15 account the commonly observed lowering of trap barrier height at higher electric field, 16 the Mott‐Gurney space charge–limited current is further modified with little variations, 17 which are evaluated and discussed in detail. 18

CNT-based displacement sensor

Abstract In this study, carbon-nanotubes-based Al/CNT/Al displacement sensors were designed, fabricated by deposition of the carbon nanotubes on an adhesive elastic polymer tape, and placed in the elastic casing, and investigated. The diameter of multiwalled nanotubes varied between 10–30 nm. The thickness of the carbon nanotube layers in the samples was 300–430 μm. The interelectrode distance (length) and width of the surface-type samples were in the range of 4–6 mm and 3–4 mm, respectively. The DC resistance of the sensors from different batches was decreased on average by 3 times as the displacement was increased up to 900 μm. The resistance–displacement relationships were supported by simulation.