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Publications
Publications (55)
Recent data loggers are computer peripheral devices or stand-alone smart instruments which can collect local databases and are able to transfer data to remote servers. Therefore, an appropriate communication protocol is required to facilitate the integration to existing computer infrastructure. This study proposes the utilization of MQTT as a commu...
Solar UV/visible monitoring has increased its importance in the recent years due to the global warming, unexpected atmospheric anomalies and storms, and the increasing needs for additional human protection. In mountain areas with high elevation the interest to UV irradiation measurements is expected to increase due to atmospheric transparency, howe...
This article focuses on the impact of the deposition temperature (in the range from 60 to 80 °C) in ZrO2 films obtained by the electrochemical deposition process on SnO2-covered glass substrates. The solution in which the deposition takes place is aqueous, containing ZrOCl2 with a concentration of 3 × 10−5 M and KCl with a concentration of 0.1 M. B...
The detection of hazardous gases at different concentration levels at low and room temperature is still an actual and challenging task. In this paper, Al-doped ZnO thin films are synthesized by the electrochemical deposition method on the gold electrodes of AT-cut quartz resonators, vibrating at 10 MHz. The average roughness, surface morphology and...
Studies are presented of electrochemically deposited nanostructured layers of ZrO2 on different conductive substrates using a thermostatic bath with a three-electrode cell as an electrochemical system. The aqueous solution in the system contained ZrOCl2 and KCl. The layers' structural properties were determined by X-ray diffraction (XRD), with the...
This article describes the research on the aging of solar photovoltaic cells in a solar power plant that has been in operation for more than 10 years. Тhe studied solar power plant is a roof structure with a power of 10kWp, and consists of three 3 syb-systems (PV strings). Two of them are based on polycrystalline-Si modules and the third one-based...
Soot is used as an electrode material for possible supercapacitance applications. The carbonaceous product is collected from a domestic heating system and possesses a naturally developed high surface area, which is one of the key requirements for such applications. The low‐molecular‐weight compounds in the soot are evaporated and carbonized by heat...
A study is presented on supercapacitor prototypes using chimney soot as the active electrode material. Despite its highly developed surface and the existence of capacitive properties, some compounds present in chimney soot make it unstable during the charge process. The irreversible electrochemical process leads to anodic oxidation and cathodic red...
Human over-exposure to solar UV radiation has been identified as a serious health problem which needs intensive screening and monitoring. The goal of this study is to present recent success in solar UV irradiation monitoring in Bulgaria in the frame of INTERGA_UV project (No. KΠ 06/24H - 2018 of National Research Fund of Bulgaria). The research eff...
A study is presented on the sensitivity of electrochemically deposited ZrO 2 and ZnO on a quartz resonator. The nanostructured ZrO 2 and ZnO layers are deposited by electrochemical method on the Au electrodes of the quartz resonators. The deposition of the electrochemical layers of ZrO 2 and ZnO is carried out in aqueous solution of (ZrOCl 2 (5. 10...
A solar thermal plant (STP) is a renewable energy source that converts heat from the sun into electricity through the chimney effect. Its main components are the chimney tower, ensuring a temperature gradient, and the collector area, converting the sun radiation into heat. The amount of electricity produced depends on the chimney dimensions, the co...
Damaging UV radiation is an important object of investigation related to its impact on biological species. Data acquired at high-altitude stations reveal dangerous events of incident UV radiation reaching the Earth surface. Continuous multi-UV spectral measurements by open-source equipment could further deepen the knowledge of solar light propagati...
Black powders were prepared from chimney soot by means of treatment with different solvents and drying. The powders were used to prepare inks, which were deposited on copper foils. The as prepared electrodes were assembled as supercapacitor structures with KOH as electrolyte. The charge-discharge characteristics were measured to evaluate the electr...
The influence of the deposition temperature (in the range from 50 to 80 • C) of the aqueous solution containing ZnCl 2 and KCl on the properties of ZnO films obtained by electrochemical deposition on SnO 2 covered glass substrates is studied. Through the implementation of X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), UV-VIS-NIR and p...
Recent advances in supercapacitor technology reveals new opportunities for energy storage devices for application in electro-transportation and renewable energy sectors. In this paper results on device fabrication are reported. A low-cost screen-printing technology to obtain electrodes of supercapacitor has been applied. The device structure is bas...
Flexible supercapacitors are attractive devices for portable applications including those integrated in clothes. Highly conducting flexible electrodes can easily be fabricated by graphene powder and PE polymer foil but reliable fabrication of supercapacitor structure is still a challenge. A promising solution could be the incorporation of conductin...
Studies and modeling of the impact of natural UV irradiation on the human population are of significant importance for human activity and economics. This paper highlights the development and initial validation of portable embedded devices for UV-A, UV-B, UV-C monitoring which are based on an open-source software architecture, narrow bandpass UV sen...
Aluminum-doped ZnO (AZO) thin films are deposited by economically-versatile fabrication method of electro-spraying onto two types of substrates-glass and silicon wafer, at substrate temperature of 300 °C, voltage of 18 kV and emitter to collector distance of 6 cm, Zinc acetate dehydrate dissolved in a mixture of deionized water, ethanol and acetic...
These works present the electrochemical deposition of ZnO nanostructured thin films on glass substrates covered by SnO 2 thin films. Nanostructured ZnO films are obtained by an electrochemical process using a three-electrode system with a saturated calomel electrode as reference electrode, in aqueous solution containing ZnCl 2 and KCl. The influenc...
The high penetration of photovoltaic (PV) installations in urban areas raises the problem of power quality and voltage stability during external atmospheric fluctuations. Densely populated PV installations, connected in a remote node of the grid may degrade power quality or multiply power fluctuations if not properly designed. Computer simulation o...
Al-doped ZnO thin films with different Al content were prepared by atomic layer deposition (ALD). To carry out thermal ALD, diethyl zinc (DEZ) and tri-methyl aluminium (TMA) were used as Zn and Al precursors, respectively, and water vapor as oxidant. Various numbers n of DEZ and m TMA cycles was used to obtain different [ZnO]n
[Al2O3]m
films, where...
In this paper, results are reported from the study of the structural and optical properties of ZnO nanostructured arrays with nanorods (NRs) grown electrochemically on ITO seeding layers with two different thicknesses deposited on a glass substrate. The properties are compared of the ZnO NRs grown on ITO seeding layers with resistivity 6.4 × 10-4 Ω...
The influence of the quartz roughness on the ZnO sorption properties is investigated. AT- cut quartz plates with differently treated surface - flat polished and unpolished ones are used. The nanostructured ZnO layers are deposited by electrochemical method on the Au electrodes of the quartz crystal micro-balances resonators (OCM). Thin ZnO nanostru...
In this paper we report results of a study of the structural and optical properties of ZnO nanostructured (NS) array layers electrochemically deposited on different conductive substrates. The following types of substrates have been used: (i) conductive multilayer stack structures glass/ZnO:Al/Ag/ZnO:Al and glass/Ag/ZnO:Al/Ag/ZnO:Al, (ii) conductive...
Large-scale PV fields are a complicated target for monitoring and performance evaluation. In this paper, field experience with multirotor UAV has been reported. A X-frame quadcopter equipped with various VIS and IR cameras is used to detect defects responsible for performance degradation. Usually in laboratory environment, hires VIS photos, EL phot...
The aim of this work is to examine the photosensitivity of dye-sensitized materials. Three types of organic dye sensitizers, i.e. perylene diimide (PDI) derivatives with different terminal groups were synthesized. The synthesized PDI derivates were deposited by dipping on a glass/ITO substrate covered with arrays of ZnO nanorods (NR) grown by an el...
The paper presents experimental results showing the possibility of liquid-phase epitaxy with a pulse-cooled substrate nano-heteroepitaxial structures with Ge quantum dots and GaP matrix for production of single-junction solar cells working under sun light concentration. The preparation of the surface of Si wafers suitable for growing of these struc...
The results of study of the optical and structural properties of ZnO nanorods (NR) arrays electrochemically deposited on two type substrates – the ITO surface on the front side of Si heterojunction (SHJ) solar cells and on stainless steel plate used for formation of a-Si:H thin film solar cells, are reported. The surface morphology of the NS arrays...
The research was fixed on sensing behavior of ZnO nanostructured (NS) films to NO2 concentrations in the environment. The ZnO NS layers are deposited by electrochemical method on quartz resonators with Au electrodes. The sorption properties of ZnO layers were defined by measuring the resonant frequency shift (Δf) of the QCM-ZnO structure for differ...
ZnO nano structured (NS) arrays are grown by electrochemical method on conductive seeding layers of ZnO doped with V (ZnO:V) deposited by magnetron sputtering on glass substrates. The surface morphology of the ZnO NS is studied by Scanning Electron Microscopy. The spectra of transmittance, diffused and specular reflectance are measured for the ZnO...
In order to improve the short-circuit current and the efficiency of silicon heterojunction solar cells, Ag grid/ITO/(p)a-Si:H/(i)a-Si:H/(n)c-Si/(i)a-Si:H/(n+)a-Si:H/Al, ZnO nanostructured (NS) array films are deposited by electrochemical method on the front side of the solar cells. Aqueous solutions of ZnCl2 and KCl at temperature of 80 °C were use...
Structural, optical, and electrical properties of multilayer stacks ZnO:Al/Ag/ZnO:Al and ZrO2/Ag/ZrO2 are studied. The stacks are deposited on glass substrates without heating by consecutive r.f. magnetron sputtering of ZnO:Al and Ag or ZrO2 and Ag targets, respectively. The properties of samples as-deposited and annealed in forming gas atmosphere,...
This paper reports studies on the sensitivity of ZnO layers to NO2 exposure. ZnO layers were fabricated by electrochemical deposition on the surface of a quartz crystal microbalance (QCM) with Au electrodes. The sensitivity was estimated using the frequency-time characteristics of the QCM. For this purpose, the resonance frequency shift was measure...
Multilayer stack structures ZnO:Al(20 nm)/Ag(x)/ZnO:Al(20 nm) with different thickness of the middle Ag(x) layer – x = 6 nm, 10 nm, 12 nm, 16 nm and 20 nm, were prepared by r.f. magnetron sputtering. The ZnO:Al and Ag layers were deposited by magnetron sputtering on glass substrates without heating. The two-layer structures ZnO:Al(20)/Ag(x) were an...
We report studies on the optical and structural properties of nanostructured ZnO layers doped with Al (ZnO NW) electrochemically grown on conductive substrates, namely, ZnO:Al/Ag/ZnO:Al multilayer stack structures deposited on glass substrates. Multilayer transparent conductive stack structures with different thickness of the middle Ag film (10 nm,...
In this paper we report results of fabrication of ordered ZnO nanorods (NRs) or nanowalls (NWs) electrochemically deposited on different highly conductive substrates. The following types of conductive substrates have been used: (i) highly doped p-type multi-crystalline Si, and (ii) copper thin plates. The influence of a seeding Ag layer deposited o...
This study addresses the optical and electrical properties of ZnO thin films doped with Al, V and Nb (ZnO:Al, ZnO:V and ZnO:Nb, respectively) deposited by r.f. magnetron sputtering in Ar atmosphere. The films are deposited on glass substrates without heating and heated at 100 °C, 150 °C and 275 °C. The optical spectra of transmittance and reflectan...
ZnO nanostructures layers are deposited by electrochemical method on different c-Si solar cells structures. Acid aqueous solutions of ZnCl2 (5. 10(-3) M) aid KCl (0.1 M) with pH 6.0 at temperature of 80 degrees C is used as electrolyte using a three-electrode electrochemical cell and saturated calomel electrodes (SCE) as a reference electrode. ZnO...
Thin films of Al2O3 with embedded Cu and Ag
nanoparticles (NPs) are deposited by r.f. co-sputtering on glass
substrates. The samples are annealed at 400°C and 500°C for 3 h
in forming gas (N2+5% H2) to stimulate Cu and Ag
nanoclusters' formation. Multilayer structures (stacks) such as
Al2O3/Ag/Al2O3,
ZnO:Al/Ag/ZnO:Al and Ag/ZnO:Al/Ag/ZnO:Al are dep...
The present work concerns the electrochemical deposition of aluminium
doped ZnO nanostructured thin films on SnO2:F covered glass
substrates. Doped with Al nanostructured ZnO (ZnO:Al) films are obtained
by an electrochemical process using a three-electrode potentiostatic
system with a saturated calomel electrode as reference electrode, in
aqueous s...
This work reports the synthesis of nanostructured ZnO by electrochemical deposition on glass substrates covered by a thin film of SnO2 doped with F (SnO2:F). Nanostructured ZnO films are deposited by an electrochemical process using a three-electrode potentiostatic system with saturated calomel electrodes as reference electrodes from an aqueous sol...
The optical and electrical properties are investigated of Nb doped ZnO (ZnO:Nb) thin films deposited by r.f. magnetron co-sputtering on glass substrates at different temperatures, Ts, between 50 °C and 500 °C. The optical transmittance and reflectance spectra are measured and used to determine the optical band gap. The values of the optical band ga...
Influence of the vanadium concentrations, CV, on the structural, optical and electrical properties of V doped ZnO thin films deposited by R.F. magnetron sputtering is studied. The CV in the films (0.41-2.46 at.%) is determined by EDAX analysis. XRD spectra show a preferential c-axis orientation along the (002) plane and average grain size is in the...
The effects of laser fluence on the growth characteristics and surface morphology of yttrium films grown by pulsed laser deposition are investigated. The presence of droplets in the deposited films, which is the main drawback of pulsed laser deposition technique, was studied at different laser fluences. The morphology and the structure of the grown...
Structural, optical and electrical properties of V doped ZnO thin films deposited by r.f. magnetron co-sputtering on glass substrates at different temperature, Ts, between 150°C and 500°C are studied. The EDS analyses indicate that the average vanadium content in the films is in the range of 0.86-0.89 at. %. XRD spectra demonstrate preferential (00...
The magnetic properties of layered HoMn2O5 monocrystals were studied in the temperature interval 4.2–150 K and in magnetic fields with the induction of up to 15 T. It was established that at room temperature the crystals have orthorhombic structure and possess ferromagnetic properties. At temperatures lower than 18 K crystals undergo phase transiti...
The structural and optical properties of nanostructured ZnO layers grown on SnO 2 :F covered glass substrate by the method of electrochemical deposition are studied. The layers are deposited from aqueous solution containing ZnCl 2 , KCl, pH 4.00 and additional supplement of ZnO powder suspension in the condition of flowing air. The influence of the...