Sergei Bereznev

Annealing effect for SnS thin films prepared by high-vacuum evaporation

Thin films of SnS are deposited onto molybdenum-coated soda lime glass substrates using the high-vacuum evaporation technique at a substrate temperature of 300 °C. The as-deposited SnS layers are then annealed in three different media: (1) H2S, (2) argon, and (3) vacuum, for different periods and temperatures to study the changes in the microstructural properties of the layers and to prepare single-phase SnS photoabsorber films. It is found that annealing the layers in H2S at 400 °C changes the stoichiometry of the as-deposited SnS films and leads to the formation of a dominant SnS2 phase. Annealing in an argon atmosphere for 1 h, however, causes no deviations in the composition of the SnS films, though the surface morphology of the annealed SnS layers changes significantly as a result of a 2 h annealing process. The crystalline structure, surface morphology, and photosensitivity of the as-deposited SnS films improves significantly as the result of annealing in vacuum, and the vacuum-annealed films are fo...

CZTS Monograin Powders and Thin Films

This paper reviews results of studies on different materials and technologies for polycrystalline solar cells conducted at Tallinn University of Technology. Structural properties and defect structure of kesterite CZTS compounds (Cu2ZnSnSe4, Cu2ZnSn(SSe)4) were studied. Influence of selenization parameters of a Zn-Cu-Sn stacked layer on the CZTS layer growth and on the morphology, distribution of elements was analyzed. All the results obtained have been used to optimize the technology of producing solar cell structures in different designs. Cu2ZnSnSe4 and, Cu2ZnSn(SSe)4 based monograin layer solar cells were developed.

Terahertz radiation from nonstoichiometric CuInSe2 films excited by femtosecond laser pulses

We report on the observation of efficient terahertz radiation from the surface of CuInSe2 excited by femtosecond laser pulses. Terahertz radiation emitted by polycrystalline CuInSe2 layers manufactured by using electrodeposition technology was as powerful as the signals radiated by single-crystalline semiconductor surfaces. It has been found that terahertz radiation efficiency is critically dependent on the stoichiometry of the CuInSe2 layers. The results of a double-pulse excitation experiment have indicated that terahertz radiation from the photoexcited surfaces of CuInSe2 samples was caused by the presence of a built-in electrical field at those surfaces.

SEM analysis and selenization of Cu-Zn-Sn sequential films produced by evaporation of metals

The formation of Cu2SnZnSe4 thin films in the selenization of different sequential metallic and alloy films is investigated. It is shown that the main process of low temperature selenization (up to 300degC) is the formation of different binary copper selenides on the layer surface. High temperature selenization (over 400degC) leads to the formation of Cu2ZnSnSe4 phase with some excess of a separate ZnSe phase. The content of ZnSe diminishes with the rise of the selenization temperature, but the selenized films stayed always multiphased. The size of the formed Cu2ZnSnSe4 crystals is controlled by the composition of the precursor.

CuInS 2 /PEDOT Photovoltaic Structure

Structures based on combination of electrically conductive polymers with inorganic semiconductors are currently intensively investigated with the aim to prepare low-cost, largearea and flexible photovoltaic devices. In this study, multilayer structures consisting of CuInS 2 (CIS) and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonate (PSS) thin films were prepared and investigated for photovoltaic applications. Polycrystalline CIS absorber layers were synthesized on top of a layered structure on Cu tape substrate using socalled non-vacuum CISCuT technique. Thin PEDOT buffer layers doped with PSS were deposited onto KCN etched and vacuum annealed CIS films. The deposition was performed using the spin-casting technique from an aqueous dispersion of PEDOT/PSS mixed with Nmethylpyrrolidone, isopropanol, glycerin and epoxysilane additives. Optimal deposition parameters for stable PEDOT films with a good adherence to the surface of CIS were selected experimentally. The morphology and thickness of prepared films and structures was determined using SEM technique. Average film thickness was about of 1.5 μm for CIS and 50 nm for PEDOT films. Current-voltage and impedance characteristics were measured. Significant photovoltage and photocurrent of the photovoltaic structures were observed under standard illumination intensity. The best structure showed an open-circuit voltage of 510 mV and a shortcircuit current density of 20.2 mA/cm 2 .

Electrochemical Behaviour of TiCN and TiAlN Gradient Coatings Prepared by Lateral Rotating Cathode Arc PVD Technology

TiCN and TiAlN gradient coatings were deposited on the AISI 316L stainless steel substrates by lateral rotating cathode arc (LARC) physical vapour deposition (PVD) technology. Corrosion and tribocorrosion behaviour was studied in 3.5 wt. % NaCl solution. The thickness of coatings was about 3 μm. For both coatings the corrosion potential shifted to more positive values as compared to the uncoated substrate. The corrosion current density decreased for TiCN and TiAlN coatings indicating up to 40 folds higher polarization resistance. The coefficient of friction value of TiCN coating is three times lower and durability is six times higher than that of TiAlN coating under the same tribocorrosion conditions.

Cu-In and Cu-Zn-Sn Films as Precursors for Production of CuInSe 2 and Cu 2 ZnSnSe 4 Thin Films

The co-sputtered Cu-In precursor layers were characterized by bi-layer surface structure in which island-type crystals were formed in a small-crystalline matrix layer. The elemental composition of the island-type crystals corresponds to the compound CuIn 2 and the matrix (area) consists of copper-rich Cu 11 In 9 phase. The surface morphology of sequentially evaporated Cu-Zn-Sn precursor layers is determined by the deposition order of stacked consistent metal layers. Precursor Mo-Sn-Zn-Cu films exhibit a well-formed “mesa-like” structure of the surface in which larger crystals (about 1,5 μm) are located on a “small-crystalline” valley. For films with other sequences of metallic layers, the mesa like structure is not so well exposed and well formed flat precursor layers were produced replacing separate metallic Cu and Sn layers with Cu/Sn alloy layer. Selenization of both Cu-In and Cu-Zn-Sn precursor layers begins with the formation of binary Cu-selenides with compositions varying with the temperature. At temperatures higher than 370 0 C the selenization of Cu-In results in single-phase CuInSe 2 films in contrast to the selenization of Sn-Zn-Cu films that results always in multi-phase films consisting of high quality Cu 2 ZnSnSe 4 crystals and of separate small-crystalline phase of ZnSe.

Hybrid solar cells based on inorganic thin film structures and conjugated polymers

Hybrid solar cells based on a combination of conductive polymer poly (3,4-ethylenedioxyth1ophene) (PEDOT) doped with polystyrenesulfonate (PSS) and inorganic semiconductor CuIn(S,Se)2 (CISSe) were investigated. The CuInSe2 (CISe) absorber layers were electrodeposited on IT0 covered glasses from aqueous solutions with various ratios of elements. The ITO/In(O,S)/CISSe photovoltaic (PV) junctions were prepared by the sulfurization of ITO/CISe precursors at 450 °C in the H2S atmosphere. A PEDOT-PSS layer of p-type is considered as an alternative for the traditional window top layer on the CISSe absorber layer in the cell structure. The polymer deposition was performed using spin-casting technique. The PV properties of the prepared ITO/In(O,S)/CISSe and ITO/In(O,S)/CISSe/PEDOT- PSS structures were investigated, with special attention paid to the role of the conductive polymer layer in the cell structure.

Electrical properties of polyaniline and polypyrrole bilayer structures

We have studied the electrical properties for conductive polyaniline (PANI) and polypyrrole (PPy). Also, bilayer structures consisted of electrochemically deposited PPy and PANI films onto PPy and PANI substrates prepared by chemical oxidative polymerization were investigated. In order to obtain structures with a high stability of electrical properties, the dopants compatibility with the polymers was studied. Special attention is given to I-V characteristics of the structures. On the basis of the experimental results, the electrical properties of bilayer structures based on PPy and PANI combined by different ways are described. In addition, the adhesive properties of different adherent layers, one to another, are discussed.

Enhanced efficiency of hybrid amorphous silicon solar cells based on single-walled carbon nanotubes and polymer composite thin film

We report a simple approach to fabricate hybrid solar cells (HSCs) based on a single-walled carbon nanotube (SWCNT) film and a thin film hydrogenated amorphous silicon (a-Si:H). Randomly oriented high quality SWCNTs with an enhanced conductivity by means of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate are used as a window layer and a front electrode. A series of HSCs are fabricated in ambient conditions with different SWCNT film thicknesses. The polymethylmethacrylate layer drop-casted on fabricated HSCs reduces the reflection fourfold and enhances the short-circuit Jsc, open-circuit Voc, and efficiency by nearly 10%. A state-of-the-art J-V performance is shown for SWCNT/a-Si HSC with an open-circuit voltage of 900 mV and efficiency of 3.4% under simulated one-sun AM 1.5G direct illumination.We report a simple approach to fabricate hybrid solar cells (HSCs) based on a single-walled carbon nanotube (SWCNT) film and thin film hydrogenated amorphous silicon (a-Si:H). Randomly oriented high-quality SWCNTs with conductivity enhanced by means of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate are used as a window layer and a front electrode. A series of HSCs are fabricated in ambient conditions with varying SWCNT film thicknesses. The polymethylmethacrylate layer drop-casted on fabricated HSCs reduces the reflection fourfold and enhances the short-circuit J sc , open-circuit V oc , and efficiency by nearly 10%. A state-of-the-art J-V performance is shown for SWCNT/a-Si HSC with an open-circuit voltage of 900 mV and an efficiency of 3.4% under simulated one-sun AM 1.5 G direct illumination.