G. S. Khrypunov

Controlled Growth of one-dimensional zinc oxide nanostructures in the pulsed electrodeposition mode

Zinc oxide nanostructures are objects of study in the field of optoelectronics, solar power engineering, nanosensorics, and catalysis. For the purpose of the controlled growth of one-dimensional submicrometer zinc oxide structures in the pulsed electrodeposition mode, the effect of the pulse electrolysis parameters on the morphology of ZnO layers, their optical properties, and structural and substructural characteristics is determined using X-ray diffraction, optical spectrophotometry, and atomic-force microscopy. The possibility of fabricating arrays of ZnO nanowires with different geometrical shapes, perpendicular to the substrate surface, by varying the frequency of cathode-substrate potential pulses is shown.

The influence of prolonged storage and forward-polarity voltage on the efficiency of CdS/CdTe-based film solar cells

The influence of storage for 48 months and subsequent effect of the forward-polarity voltage on the operational efficiency of film solar cells with the starting layered structure n+-ITO/n-CdS/p-CdTe/Cu/Au is investigated by the methods of the current-voltage and capacitance-voltage characteristics. A physical model of degradation of this type of solar cells under the influence of the mentioned factors is improved based on the obtained results. The conditions are determined under which partial efficiency restoration of these cells after their degradation is possible via holding at room temperature under a forward bias voltage of the p-n heterojunction lower that the open-circuit voltage.

Prospects for the pulsed electrodeposition of zinc-oxide hierarchical nanostructures

Studies into the effect of the conditions of pulsed electrodeposition upon the structural and sub-structural parameters, morphology, and optical properties of ZnO-crystallite arrays make it possible to establish those parameters optimal for the formation of ZnO nanorods oriented normally to the substrate surface. These parameters are as follows: an electrolyte temperature of 70–85°C, duty cycle of 40%, and a pulse-repetition frequency of 2 Hz. The nanorod dimensions can be varied by heating or cooling the electrolyte within the above-indicated limits; as a result, small-sized nanorods can be electrically deposited on the surface of larger nanorods to form hierarchical nanostructures. By varying the duty cycle, it is possible to modify the surface morphology of the arrays up to the formation of mesoporous ZnO networks. In combination with ZnO nanorods, such networks are capable of forming hierarchical nanostructures with large specific areas.

Features of the light current-voltage characteristics of bifacial solar cells based on thin CdTe layers

It is shown that the features of the illuminated current-voltage characteristics of bifacial solar cells glass/SnO2:F/CdS/CdTe/Cu/ITO with a thin base layer are associated with the photovoltaic effect at the back contact. An equivalent circuit of the device structure under study, which takes into account the existence of two illuminated diodes—a frontal diode (main separating barrier) and a diode at a back contact—is suggested.

Solar selective absorber based on zinc oxide-nickel cermet

The efficiency of solar thermal collectors strongly depends on the optical properties of solar selective materials used in their design since the solar absorber surfaces should have high solar absorptance in the wavelength range of 0.3–2.5 µm and low thermal emittance in the infrared region (beyond 2.5 µm). Different design principles are developed for achieving of spectral selectivity. They are creation of intrinsic selective absorbers, multilayer absorbers, absorbers based on quantum size effect or on textured surfaces, absorber-reflector tandems (semiconductor-metal tandem or composite coatings), heat mirrors [1]. Different techniques were used for the obtaining of selective solar absorber surfaces such as sputtering, evaporation, electroplating, or they can be sprayed or spread as a paint [1]. Among the above mentioned designs of selective surfaces the composite coatings (also called cermets) attract significant attention due to their strong absorption in the solar spectrum range and transparency in the infrared. Usually, the cermet coatings consist of nanoscale metal particles embedded in a dielectric matrix, generally SiO 2 , Al 2 O 3 , and MgO, deposited on a highly infrared reflecting metal substrate like bulk Cu and Al plates or coated by Al or Cu thin films glass substrates. Particles of metals with high melting points such as Cu, Au, Ni, Mo, Cr, Co, etc. are commonly used as filler materials with dielectric matrixes. The absorbing cermet layer may have either uniform or graded metal content. An antireflective coating can be deposited on the top of cermet stack with the aim to reduce the refractive index mismatch between air and the absorbing layer. Intrinsic high resistive zinc oxide ZnO can be used as alternative to above mentioned conventional ceramic matrix materials [2]. ZnO has attracted increasing interest due to its unique ability to form a variety of nanostructures, especially in the form of vertically arranged one-dimensional (1D) nanorod arrays. The various methods have been developed for production of the well-ordered 1D ZnO nanostructures which are suitable for applications in various devices such as short-wavelength lasers, sensors, photocatalytic systems and for solar cells of third generation [2]. In comparison with high vacuum technologies pulse electrochemical deposition has high potential due to a more efficient material consumption and low investment costs. It is possible to control the preferred orientation of ZnO films and their morphology by changing such pulse parameters like the cathodic average current density or cathode on/off potentials, the pulse length, the pulse shape and the pulse period.

Investigation of Thin Film Solar Cells on CdS/CdTe Base with Different Back Contacts

The peculiarities of photo-electric processes in thin film CdS/CdTe solar cells (SC) with different back electrodes (Cu/Au, ITO, Cu/ITO) have been studied. As it was established by capacitance – voltage (C – V) characteristics, the potential barrier heights for CdTe/Cu/Au and CdTe/ITO were 0.3 eV and 2.2 eV, respectively. The concentrations of charge carriers near back contact consisted 91020 m–3 and 21021 m–3, respectively. A high carrier concentration and high potential barrier of the ITO back contact caused the tunnel – recombination mechanism of the charge transport. The investigations of CdS/CdTe/ITO SC spectral photosensitivity testify a negative impact of the developed grain-boundary surface of the base layer on the processes of diffusion and separation of non-equilibrium current carriers generated by short-wave radiation. It is shown that the deposition of Cu nanolayer before the deposition of ITO films give stable efficiency 10 % for bifacial CdS/CdTe solar cells.

Adopting of DC magnetron sputtering method for preparing semiconductor films

It has been carried out the experimental studies of the process of cadmium telluride magnetron sputtering with direct current, and the impact of a magnetron sputtering mode on CdTe films crystalline structure. In order to create thin-film solar cells based on cadmium sulfide and telluride CdTe films for the base layers of thin film solar cells was obtained on flexible polyimide substrates by magnetron sputtering with direct current for the first time. It has found that increasing the magnetron discharge current up to 80 mA leads to increase in coherent scattering regions what is due to an increase in the thickness of the cadmium telluride films of the hexagonal modification having a columnar structure.

Properties of CdTe films prepared by DC magnetron sputtering

In order to create thin-film solar cells based on cadmium sulfide and telluride experimental studies of the process of cadmium telluride magnetron sputtering with direct current, and the impact of a magnetron sputtering mode on CdTe films crystalline structure were carried out. CdTe films for the base layers of thin film solar cells was obtained on flexible polyimide substrates by magnetron sputtering with direct current for the first time. It has found that increasing the magnetron discharge current up to 80 mA leads to increase in coherent scattering regions what is due to an increase in the thickness of the cadmium telluride films of the hexagonal modification having a columnar structure. A further increase in the discharge current leads to a decrease in the size of coherent scattering regions what caused by the thermodynamical output formation of low-angle boundaries. It has shown experimentally that the “chloride” processing of the obtained cadmium telluride layer leads to the transformation of the metastable hexagonal modification cadmium telluride in a stable cubic modification. At the same time, due to the eutectic recrystallization, increase in the sizes of coherent scattering regions by a decade and the microstrain level reduction in 1.5 times are observed.

Development of hybrid solar generating module for high-efficiency solar energy station

Experimentally established, the influence of the working temperature and solar radiation power on the efficiency of industrial production silicon solar cells. Based on the experimental results designed the concept of a hybrid solar generating module equipped with a mirror concentrator of solar radiation and solar cells cooling system for using in high-performance solar energy station. Concentrator of solar radiation provides in 1.5-time increase of electrical power generating by such module, and water-cooling system can reduce the equilibrium temperature of the module up to 10 degrees and twice reduce efficiency losses from solar cells overheating. The proposed concept will reduce the number of modules needed to build solar energy station.