In this work we present the results on formation of ZnO nanorods prepared by spray of aqueous sol... more In this work we present the results on formation of ZnO nanorods prepared by spray of aqueous solutions containing ZnCl2 and thiocarbamide (tu) at different molar ratios. It has been observed that addition of thiocarbamide into the spray solution has great impact on the size, shape and phase composition of the ZnO crystals. Obtained layers were characterized by scanning electron microscopy (SEM) equipped with energy selected backscattered electron detection system (ESB), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). Small addition of thiocarbamide into ZnCl2 solution (ZnCl2:tu = 1:0.25) supports development of significantly thinner ZnO nanorods with higher aspect ratio compared to those obtained from ZnCl2 solution. Diameter of ZnO rods decreases from 270 to 100 nm and aspect ratio increases from ~2.5 to 12 spraying ZnCl2 and ZnCl2:tu solutions, respectively. According to XRD, well crystallized (002) orientated pure wurtzite ZnO crystals have been formed. However,...
In the present study nanostructured solar cells were prepared by in-line spray pyrolysis techniqu... more In the present study nanostructured solar cells were prepared by in-line spray pyrolysis technique. ETA cells were realized on ZnO nanorod layer using CuInS2 as an absorber material. Thin layers of TiO2 or indium sulfide (In-S) were deposited by spray onto ZnO nanorods in order to prevent the ZnO crystals from dissolution during the deposition of acidic solutions to form the next layers of the cell. Insertion of both TiO2 and In-S layers into the cell structure reduces the electrical shorts between front and back contact. Thickness of TiO2 layer should be carefully controlled as at certain thickness it blocks the charge carrier transport in the device. The use of structured layer with ZnO nanorods (L~ 500 nm) increases the current density from 5-6 mA/cm2 up to 11-14 mA/cm2 with no significant reduction in Voc and FF compared to the planar device. Further increasing of the rod length leads to the higher current densities but decreases the open circuit voltage due to increased recombination at higher interface area. The conversion efficiency of 3.9 % (Voc=463 mV, j=14 mA/cm2, FF=60%) is obtained for the structure TCO/ZnO(rod)/barrier/In2S3/CuInS2/PEDOT:PSS prepared at very low cost.
In this study various morphologies of ZnO including rods, disks, and nanosheets network were synt... more In this study various morphologies of ZnO including rods, disks, and nanosheets network were synthesised by electrodeposition method. The influence of the SeO 2 additive concentration on morphological, structural, and optical properties of ZnO was studied by using scanning electron microscopy, X-ray diffractometry (XRD), energy-dispersive X-ray analysis (EDX), optical (UV-Vis) and photoluminescence (PL) spectroscopy methods. The formation of the disk-like ZnO structure with a diameter of ca. 300-500 nm and thickness ca. 80-100 nm was observed when 0.03 mmol/L of SeO 2 was added to the solution. Further increase of dopant concentration up to 0.2 mmol/L in the solution yielded a highly-porous network structure composed of thin nanosheets with a wall thickness of ca. 20 nm. According to the XRD results, all structures were composed of ZnO, rod-like crystals were strongly c-axis oriented, whereas disks and nanosheets network structures were a-axis oriented. EDX analysis revealed that Se was present in the disks and nanosheets structures. PL study of the rod sample showed UV emission at~370 nm, whereas the disks and nanosheets network showed intense deep-level emission band centred at~540 nm. The disks and nanosheets exhibited total transmittance of ∼80-90% in the region of 380-780 nm, whereas transmittance of the rods was increasing from 5% to 50% in this region. According to haze factor calculations, samples possessed scattering ability of 20% for disks, 45% for sheets and ca. 50% for rods. The probable mechanism for the formation of ZnO structures was discussed in detail.
ZnO is an important inorganic material for numerous applications. Different physical and chemical... more ZnO is an important inorganic material for numerous applications. Different physical and chemical methods have been applied to deposit ZnO. Spray pyrolysis method being simple, rapid and low-cost is amongst the many options and has been chosen for this study. Fabrication of ZnO nanorods crystals by chemical spray pyrolysis was performed using acidic solution of ZnCl 2 1 or basic ammonia containing solution of ZnCl 2 2. All layers were studied using X-ray diffractometry and Scanning Electron Microscopy. The formation of ZnO nanorods from 2 appeared at 450 °C, whereas spraying acidic solution 1 yielded ZnO nanorods like morphology at 550 °C. Thermal decomposition of precursors for ZnO layers prepared by de-watering of acidic aqueous solution of ZnCl 2 with pH = 3 (1) and basic solution of ZnCl 2 and NH 4 OH with pH = 10 (2) was monitored by simultaneous thermogravimetric and differential thermal analysis (TG/DTA) in air coupled online with evolved gas analyses by Fourier transformed infrared spectroscopy (FTIR). The precursor (1) is ZnCl 2 *nH 2 O; the precursor (2) is a mixture of (NH 4) 3 (ZnCl 4)Cl, Zn(NH 3) 2 Cl 2 , NH 4 Cl(NH 3) 3 and Zn(OH) 2 phases. The thermal decomposition of (1) and (2) in the temperature range of 30-700 °C consists of two steps with total mass losses of 86.2% and 93.8%, respectively. The main evolved gases from (1) are H 2 O and HCl, whereas the main evolved gases from (2) are H 2 O, NO x and NH 3. Degradation of (1) and (2) is completed by 670 and 620 °C, respectively. The final decomposition product of (1) and (2) at 700 °C is ZnO. This study shows that the use of basic solutions enables to decrease the temperature of ZnO formation and the deposition temperature of ZnO nanorods layers.
The experimental research into the aqueous photocatalytic oxidation of doxycycline, a tetracyclin... more The experimental research into the aqueous photocatalytic oxidation of doxycycline, a tetracycline family antibiotic, was undertaken. The objective of the study was to ensure the feasibility of doxycycline photocatalytic degradation by UVA irradiated titania coatings on granulated media to be used in fluidised bed photocatalytic reactor and by slurries of P25, Evonik, as well as by visible light-sensitive sol-gel synthesized carbon-containing titania. The parameters influencing doxycycline oxidation, like catalyst concentration, initial doxycycline concentration and pH with P25 TiO
The cost-effective spray pyrolysis technique was applied to prepare ZnS thin films for large-scal... more The cost-effective spray pyrolysis technique was applied to prepare ZnS thin films for large-scale applications. Aqueous solutions containing ZnCl2 and SC(NH2)2 were deposited onto glass and n-type Si(100) substrates at 430-600°C. The structure and phase composition were studied by XRD and FTIR, the surface morphology by SEM. The optical properties were determined from the transmittance and reflectance measurements in the UV-visible and near-IR regions. The phase composition, crystallinity, and surface morphology of the films could be controlled by the Zn : S molar ratio in the stock solution and the deposition temperature. Highly (001) oriented ZnS films with wurtzite structure were grown at temperatures above 500°C using the Zn:S molar ratio 1 :2 in the solution. The sprayed films had high optical transmittance in a wide spectral range and the refractive index of up to 1.9 at 632.8 nm. It was also found that the sprayed ZnS films are capable of being used as antireflection coatings in Si-based devices.
ABSTRACT The In(OH)xSy thin films were deposited by chemical bath deposition (CBD) using three di... more ABSTRACT The In(OH)xSy thin films were deposited by chemical bath deposition (CBD) using three different deposition procedures: ‘hot’: starting the deposition at 70 °C, ‘cold’: starting the deposition at room temperature and pre-treatment with In3+ ions prior the ‘hot’ deposition. The analysis of the deposited In(OH)xSy layers on glass revealed that modifications in the chemical bath deposition procedure provoked significant changes in the nucleation process, the growth rate, the layer elemental composition and the layer morphology. With an additional In3+ pre-treatment or starting from a cold solution, the formation of a dense bottom layer has been observed, resulting in In(OH)xSy films with more compact structure with refractive index values of 2.6. The comparison of the measured In/S ratio with a thicker layer suggests, that the In(OH)xSy deposition starts with an OH-rich layer. Assuming the indirect allowed band gap transition type, an Eg of 2.2 eV was found independent of the procedure type or deposition time.
ZnO-TiO 2 core shell Chemical spray pyrolysis ALD Sol-gel spray Electrical properties ZnO nanostr... more ZnO-TiO 2 core shell Chemical spray pyrolysis ALD Sol-gel spray Electrical properties ZnO nanostructured solar cells with CuInS 2 absorber layer were prepared by chemical spray method. In order to increase chemical stability of ZnO nanorods against dissolution in the next steps of the cell preparation, and reduce the electrical shorts between the front and back contacts, an amorphous TiO 2 layer was deposited on ZnO nanorods by ALD or sol-gel spray technique. The thicknesses of the layer (≤ 5 nm by spray and ≤ 1 nm by ALD), which did not impede the collection of carriers, were determined. TiO 2 thicknesses above these optimal values led to s-shaped I-V curves, causing the decrease in solar cell efficiency from 2.2 to 0.7% due to the formation of an additional junction blocking charge carrier transport in the device under forward bias. Nanostructured cells suffered from somewhat higher interface recombination but showed still two times higher current densities (~10 mA/cm 2) than the planar devices did.
The paper summarizes the results of R/D in new alternative materials and in thin film and monogra... more The paper summarizes the results of R/D in new alternative materials and in thin film and monograin solar cells at EU Centre of Excellence in PV Materials and Devices at TUT. The defect structure of various chalcopyrite compounds (CuInSe 2 , CuInS 2 , CuGaSe 2 , CuGaTe 2 , AgGaTe 2 , CuInTe 2 , AgInTe 2, Cu 2 ZnSnSe 4) was studied. A novel route of spray deposition was developed to prepare ZnO layers comprising nanorods as a promising material for solar cells. Technological conditions for controlled ZnS chemical bath deposition were determined. The influence of parameters of electrodeposition and annealings in different atmosphere to the composition and morphology of CuInSe 2 thin films was studied. Hybrid solar cells on the basis of CuInS 2 and CdTe photoabsorbers in combination with organic functional layers were prepared and investigated. All the obtained results were used to optimize the technology of producing solar cell structures in different designs.
ABSTRACT ZnO nanorods were prepared by a spray pyrolysis technique on both as-received and etched... more ABSTRACT ZnO nanorods were prepared by a spray pyrolysis technique on both as-received and etched Indium Tin Oxide (ITO)/glass substrates. The morphologies of the ITO substrates, the ZnO nucleation mechanism and the development of ZnO nanorods on both types of ITO substrates were investigated by Atomic Force Microscopy and Scanning Electron Microscopy methods. It was found that the amount of nucleation sites on as-received ITO is significantly higher compared to that on the etched ITO. As a result, well-shaped, elongated, strongly c-axis-oriented ZnO nanorods were obtained on the etched ITO/glass substrates. In contrast, randomly oriented ZnO nanocrystals with different shapes and sizes, as well as low aspect ratios, were obtained on the as-received substrates. It was found that ZnO nucleation follows the grain-boundary nucleation mechanism.
In this paper we present a realization of an extremely thin absorber (ETA) layer solar cell by th... more In this paper we present a realization of an extremely thin absorber (ETA) layer solar cell by the chemical spray pyrolysis method. CuInS 2 absorber was deposited onto a blocking layer coated ZnO nanorods grown on a transparent conductive oxide. Layers and cells were characterized by optical and Raman spectroscopy, and scanning electron microscopy. Current-voltage, spectral response and electron beam induced current measurements were applied to solar cells. ZnO nanorod cell showed twice higher short circuit current density than the flat reference. ETA cells with efficiency of 2.2% (j ¼ 12 mA/cm 2 , V oc ¼ 425 mV, FF ¼ 43%) and of 2.5% were prepared using TiO 2-anatase and an indium sulfide blocking layer, respectively.
ZnS thin films were prepared by spray pyrolysis technique using aqueous solutions of zinc chlorid... more ZnS thin films were prepared by spray pyrolysis technique using aqueous solutions of zinc chloride and thiourea at molar ratio of 1:1, 1:2 and 2:1. The films were characterized by XRD, FTIR, SEM and EDX. The phase composition, structure and morphology of sprayed films are controlled by both, the substrate temperature and the precursors molar ratio in the solution. The films deposited below 380 ºC are amorphous and contain thermal decomposition residues of Zn(tu) 2 Cl 2. Chlorine content becomes negligible at 500 ºC, carbon and nitrogen in the form of zinc cyanamide are present in a trace amount up to 540 ºC. Highly (002) orientated ZnS films with wurtzite structure and closely stoichiometric composition could be grown at temperatures close to 500 ºC using Zn:S molar ratio of 1:2 in spray solution. The film consists of well-shaped hexagonal prisms with size of 100 nm. The spray of equimolar solution (Zn:S = 1:1) results in ZnS films with smaller grain size (~25 nm) and slightly Zn-rich composition at 500 ºC. Higher temperature (530 ºC) is needed to grow the films with wurtzite structure. The use of Zn-rich (Zn/S>1) solution results in the films consisting of ZnO and ZnS phases above 400 ºC.
The ZnS layers morphology, structure, composition, and optical properties were investigated with ... more The ZnS layers morphology, structure, composition, and optical properties were investigated with respect to the precursors (zinc chloride and thiocarbamide, Zn:S) molar ratio in spray solution (1:1, 1:2, and 1:3) and growth temperatures in the range of 400–600 °C. Scanning electron microscopy (SEM), X‐ray diffraction (XRD), energy dispersive X‐ray analysis (EDX), UV–VIS, and PL spectroscopy were applied to characterize the ZnS layers. Layers obtained at temperatures up to 450 °C are not well crystallized and contain residues originated from undecomposed precursors. ZnS films become crystalline at Ts = 500 °C. Layers grown from 1:1 solution at 550 °C are mixture of ZnS and ZnO phases, whereas at 600 °C layers of ZnO were obtained. Films produced from 1:2 solution at 500–600 °C are of ZnS with a wurtzite structure and Eg of 3.66 eV, but contain traces of ZnO phase when grown at 550 or 600 °C. Appearance of ZnO phase in the films grown from 1:1 and 1:2 solutions is explained by the res...
Photocatalysts synthesized by sol-gel method inevitably incorporate carbon together with dopants.... more Photocatalysts synthesized by sol-gel method inevitably incorporate carbon together with dopants. The objective of the research consists in the synthesis and testing of photocatalytic activity of car bon containing titanium dioxide photocatalysts calcinated at various temperatures. The optical and struc tural properties of the catalysts were also studied. The activity was tested in visible light in aqueous photocat alytic oxidation of three various type pollutants, methyl tert butyl ether, p toluidine and phenol, where the divergent character of the C-TiO 2 catalysts was distinctively observed: methyl tert butyl ether and p tolui dine were oxidized with the efficiency close to or even surpassing that of UV irradiated P25 (Evonik), whereas phenol was oxidized poorly. The observed photocatalytic activity, where quantum efficiency varied from 0.6 to 2.3 and from 0.1 to 1.2% for p toluidine and phenol degradation respectively, may be explained by the different electrostatic properties of the catalysts' surface and the tested substances, i.e. their interac tion. This compromises the widespread usage of phenol as a reference substance for comparison of catalytic activities of catalysts.
IOP Conference Series: Materials Science and Engineering, 2013
ZnO layers comprizing rods were deposited by chemical spray pyrolysis (CSP) method at 520 ˚C on d... more ZnO layers comprizing rods were deposited by chemical spray pyrolysis (CSP) method at 520 ˚C on different FTO (SnO2:F)/glass substrates using zinc chloride aqueous solutions. Substrates were purchased from different manufactures and differ by morphology, grain size and roughness of FTO electrode. FTO/glass substrates and ZnO layers grown on them were characterised with the help of XRD, AFM, high resolution SEM, EDX methods. The relationship between nanorod formation and substrate properties was studied. It was found that substrate roughness and grain size influence the ZnO rods formation. Deposition of rods (d=300 nm, L=1.4 μm) was successful on the FTO layers with grain sizes around 30-50 nm and roughness below 10 nm, whereas large-grained FTO (grain size > 130 nm) resulted in thick, lowaspect ratio crystals with diameter around 400 nm and length of about 400 nm.
Surface properties of spray and electrodeposited rods were studied and compared Influence of hy... more Surface properties of spray and electrodeposited rods were studied and compared Influence of hydroxyl groups on the surface of as-deposited ZnO rods was observed Higher amount of hydroxyl groups on electrodeposited rods makes surface hydrophilic Impact of hydroxyl groups of aged samples is shaded by contamination within time Wettability of sprayed samples didn't change significantly within storage time
In this work we present the results on formation of ZnO nanorods prepared by spray of aqueous sol... more In this work we present the results on formation of ZnO nanorods prepared by spray of aqueous solutions containing ZnCl2 and thiocarbamide (tu) at different molar ratios. It has been observed that addition of thiocarbamide into the spray solution has great impact on the size, shape and phase composition of the ZnO crystals. Obtained layers were characterized by scanning electron microscopy (SEM) equipped with energy selected backscattered electron detection system (ESB), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). Small addition of thiocarbamide into ZnCl2 solution (ZnCl2:tu = 1:0.25) supports development of significantly thinner ZnO nanorods with higher aspect ratio compared to those obtained from ZnCl2 solution. Diameter of ZnO rods decreases from 270 to 100 nm and aspect ratio increases from ~2.5 to 12 spraying ZnCl2 and ZnCl2:tu solutions, respectively. According to XRD, well crystallized (002) orientated pure wurtzite ZnO crystals have been formed. However,...
In the present study nanostructured solar cells were prepared by in-line spray pyrolysis techniqu... more In the present study nanostructured solar cells were prepared by in-line spray pyrolysis technique. ETA cells were realized on ZnO nanorod layer using CuInS2 as an absorber material. Thin layers of TiO2 or indium sulfide (In-S) were deposited by spray onto ZnO nanorods in order to prevent the ZnO crystals from dissolution during the deposition of acidic solutions to form the next layers of the cell. Insertion of both TiO2 and In-S layers into the cell structure reduces the electrical shorts between front and back contact. Thickness of TiO2 layer should be carefully controlled as at certain thickness it blocks the charge carrier transport in the device. The use of structured layer with ZnO nanorods (L~ 500 nm) increases the current density from 5-6 mA/cm2 up to 11-14 mA/cm2 with no significant reduction in Voc and FF compared to the planar device. Further increasing of the rod length leads to the higher current densities but decreases the open circuit voltage due to increased recombination at higher interface area. The conversion efficiency of 3.9 % (Voc=463 mV, j=14 mA/cm2, FF=60%) is obtained for the structure TCO/ZnO(rod)/barrier/In2S3/CuInS2/PEDOT:PSS prepared at very low cost.
In this study various morphologies of ZnO including rods, disks, and nanosheets network were synt... more In this study various morphologies of ZnO including rods, disks, and nanosheets network were synthesised by electrodeposition method. The influence of the SeO 2 additive concentration on morphological, structural, and optical properties of ZnO was studied by using scanning electron microscopy, X-ray diffractometry (XRD), energy-dispersive X-ray analysis (EDX), optical (UV-Vis) and photoluminescence (PL) spectroscopy methods. The formation of the disk-like ZnO structure with a diameter of ca. 300-500 nm and thickness ca. 80-100 nm was observed when 0.03 mmol/L of SeO 2 was added to the solution. Further increase of dopant concentration up to 0.2 mmol/L in the solution yielded a highly-porous network structure composed of thin nanosheets with a wall thickness of ca. 20 nm. According to the XRD results, all structures were composed of ZnO, rod-like crystals were strongly c-axis oriented, whereas disks and nanosheets network structures were a-axis oriented. EDX analysis revealed that Se was present in the disks and nanosheets structures. PL study of the rod sample showed UV emission at~370 nm, whereas the disks and nanosheets network showed intense deep-level emission band centred at~540 nm. The disks and nanosheets exhibited total transmittance of ∼80-90% in the region of 380-780 nm, whereas transmittance of the rods was increasing from 5% to 50% in this region. According to haze factor calculations, samples possessed scattering ability of 20% for disks, 45% for sheets and ca. 50% for rods. The probable mechanism for the formation of ZnO structures was discussed in detail.
ZnO is an important inorganic material for numerous applications. Different physical and chemical... more ZnO is an important inorganic material for numerous applications. Different physical and chemical methods have been applied to deposit ZnO. Spray pyrolysis method being simple, rapid and low-cost is amongst the many options and has been chosen for this study. Fabrication of ZnO nanorods crystals by chemical spray pyrolysis was performed using acidic solution of ZnCl 2 1 or basic ammonia containing solution of ZnCl 2 2. All layers were studied using X-ray diffractometry and Scanning Electron Microscopy. The formation of ZnO nanorods from 2 appeared at 450 °C, whereas spraying acidic solution 1 yielded ZnO nanorods like morphology at 550 °C. Thermal decomposition of precursors for ZnO layers prepared by de-watering of acidic aqueous solution of ZnCl 2 with pH = 3 (1) and basic solution of ZnCl 2 and NH 4 OH with pH = 10 (2) was monitored by simultaneous thermogravimetric and differential thermal analysis (TG/DTA) in air coupled online with evolved gas analyses by Fourier transformed infrared spectroscopy (FTIR). The precursor (1) is ZnCl 2 *nH 2 O; the precursor (2) is a mixture of (NH 4) 3 (ZnCl 4)Cl, Zn(NH 3) 2 Cl 2 , NH 4 Cl(NH 3) 3 and Zn(OH) 2 phases. The thermal decomposition of (1) and (2) in the temperature range of 30-700 °C consists of two steps with total mass losses of 86.2% and 93.8%, respectively. The main evolved gases from (1) are H 2 O and HCl, whereas the main evolved gases from (2) are H 2 O, NO x and NH 3. Degradation of (1) and (2) is completed by 670 and 620 °C, respectively. The final decomposition product of (1) and (2) at 700 °C is ZnO. This study shows that the use of basic solutions enables to decrease the temperature of ZnO formation and the deposition temperature of ZnO nanorods layers.
The experimental research into the aqueous photocatalytic oxidation of doxycycline, a tetracyclin... more The experimental research into the aqueous photocatalytic oxidation of doxycycline, a tetracycline family antibiotic, was undertaken. The objective of the study was to ensure the feasibility of doxycycline photocatalytic degradation by UVA irradiated titania coatings on granulated media to be used in fluidised bed photocatalytic reactor and by slurries of P25, Evonik, as well as by visible light-sensitive sol-gel synthesized carbon-containing titania. The parameters influencing doxycycline oxidation, like catalyst concentration, initial doxycycline concentration and pH with P25 TiO
The cost-effective spray pyrolysis technique was applied to prepare ZnS thin films for large-scal... more The cost-effective spray pyrolysis technique was applied to prepare ZnS thin films for large-scale applications. Aqueous solutions containing ZnCl2 and SC(NH2)2 were deposited onto glass and n-type Si(100) substrates at 430-600°C. The structure and phase composition were studied by XRD and FTIR, the surface morphology by SEM. The optical properties were determined from the transmittance and reflectance measurements in the UV-visible and near-IR regions. The phase composition, crystallinity, and surface morphology of the films could be controlled by the Zn : S molar ratio in the stock solution and the deposition temperature. Highly (001) oriented ZnS films with wurtzite structure were grown at temperatures above 500°C using the Zn:S molar ratio 1 :2 in the solution. The sprayed films had high optical transmittance in a wide spectral range and the refractive index of up to 1.9 at 632.8 nm. It was also found that the sprayed ZnS films are capable of being used as antireflection coatings in Si-based devices.
ABSTRACT The In(OH)xSy thin films were deposited by chemical bath deposition (CBD) using three di... more ABSTRACT The In(OH)xSy thin films were deposited by chemical bath deposition (CBD) using three different deposition procedures: ‘hot’: starting the deposition at 70 °C, ‘cold’: starting the deposition at room temperature and pre-treatment with In3+ ions prior the ‘hot’ deposition. The analysis of the deposited In(OH)xSy layers on glass revealed that modifications in the chemical bath deposition procedure provoked significant changes in the nucleation process, the growth rate, the layer elemental composition and the layer morphology. With an additional In3+ pre-treatment or starting from a cold solution, the formation of a dense bottom layer has been observed, resulting in In(OH)xSy films with more compact structure with refractive index values of 2.6. The comparison of the measured In/S ratio with a thicker layer suggests, that the In(OH)xSy deposition starts with an OH-rich layer. Assuming the indirect allowed band gap transition type, an Eg of 2.2 eV was found independent of the procedure type or deposition time.
ZnO-TiO 2 core shell Chemical spray pyrolysis ALD Sol-gel spray Electrical properties ZnO nanostr... more ZnO-TiO 2 core shell Chemical spray pyrolysis ALD Sol-gel spray Electrical properties ZnO nanostructured solar cells with CuInS 2 absorber layer were prepared by chemical spray method. In order to increase chemical stability of ZnO nanorods against dissolution in the next steps of the cell preparation, and reduce the electrical shorts between the front and back contacts, an amorphous TiO 2 layer was deposited on ZnO nanorods by ALD or sol-gel spray technique. The thicknesses of the layer (≤ 5 nm by spray and ≤ 1 nm by ALD), which did not impede the collection of carriers, were determined. TiO 2 thicknesses above these optimal values led to s-shaped I-V curves, causing the decrease in solar cell efficiency from 2.2 to 0.7% due to the formation of an additional junction blocking charge carrier transport in the device under forward bias. Nanostructured cells suffered from somewhat higher interface recombination but showed still two times higher current densities (~10 mA/cm 2) than the planar devices did.
The paper summarizes the results of R/D in new alternative materials and in thin film and monogra... more The paper summarizes the results of R/D in new alternative materials and in thin film and monograin solar cells at EU Centre of Excellence in PV Materials and Devices at TUT. The defect structure of various chalcopyrite compounds (CuInSe 2 , CuInS 2 , CuGaSe 2 , CuGaTe 2 , AgGaTe 2 , CuInTe 2 , AgInTe 2, Cu 2 ZnSnSe 4) was studied. A novel route of spray deposition was developed to prepare ZnO layers comprising nanorods as a promising material for solar cells. Technological conditions for controlled ZnS chemical bath deposition were determined. The influence of parameters of electrodeposition and annealings in different atmosphere to the composition and morphology of CuInSe 2 thin films was studied. Hybrid solar cells on the basis of CuInS 2 and CdTe photoabsorbers in combination with organic functional layers were prepared and investigated. All the obtained results were used to optimize the technology of producing solar cell structures in different designs.
ABSTRACT ZnO nanorods were prepared by a spray pyrolysis technique on both as-received and etched... more ABSTRACT ZnO nanorods were prepared by a spray pyrolysis technique on both as-received and etched Indium Tin Oxide (ITO)/glass substrates. The morphologies of the ITO substrates, the ZnO nucleation mechanism and the development of ZnO nanorods on both types of ITO substrates were investigated by Atomic Force Microscopy and Scanning Electron Microscopy methods. It was found that the amount of nucleation sites on as-received ITO is significantly higher compared to that on the etched ITO. As a result, well-shaped, elongated, strongly c-axis-oriented ZnO nanorods were obtained on the etched ITO/glass substrates. In contrast, randomly oriented ZnO nanocrystals with different shapes and sizes, as well as low aspect ratios, were obtained on the as-received substrates. It was found that ZnO nucleation follows the grain-boundary nucleation mechanism.
In this paper we present a realization of an extremely thin absorber (ETA) layer solar cell by th... more In this paper we present a realization of an extremely thin absorber (ETA) layer solar cell by the chemical spray pyrolysis method. CuInS 2 absorber was deposited onto a blocking layer coated ZnO nanorods grown on a transparent conductive oxide. Layers and cells were characterized by optical and Raman spectroscopy, and scanning electron microscopy. Current-voltage, spectral response and electron beam induced current measurements were applied to solar cells. ZnO nanorod cell showed twice higher short circuit current density than the flat reference. ETA cells with efficiency of 2.2% (j ¼ 12 mA/cm 2 , V oc ¼ 425 mV, FF ¼ 43%) and of 2.5% were prepared using TiO 2-anatase and an indium sulfide blocking layer, respectively.
ZnS thin films were prepared by spray pyrolysis technique using aqueous solutions of zinc chlorid... more ZnS thin films were prepared by spray pyrolysis technique using aqueous solutions of zinc chloride and thiourea at molar ratio of 1:1, 1:2 and 2:1. The films were characterized by XRD, FTIR, SEM and EDX. The phase composition, structure and morphology of sprayed films are controlled by both, the substrate temperature and the precursors molar ratio in the solution. The films deposited below 380 ºC are amorphous and contain thermal decomposition residues of Zn(tu) 2 Cl 2. Chlorine content becomes negligible at 500 ºC, carbon and nitrogen in the form of zinc cyanamide are present in a trace amount up to 540 ºC. Highly (002) orientated ZnS films with wurtzite structure and closely stoichiometric composition could be grown at temperatures close to 500 ºC using Zn:S molar ratio of 1:2 in spray solution. The film consists of well-shaped hexagonal prisms with size of 100 nm. The spray of equimolar solution (Zn:S = 1:1) results in ZnS films with smaller grain size (~25 nm) and slightly Zn-rich composition at 500 ºC. Higher temperature (530 ºC) is needed to grow the films with wurtzite structure. The use of Zn-rich (Zn/S>1) solution results in the films consisting of ZnO and ZnS phases above 400 ºC.
The ZnS layers morphology, structure, composition, and optical properties were investigated with ... more The ZnS layers morphology, structure, composition, and optical properties were investigated with respect to the precursors (zinc chloride and thiocarbamide, Zn:S) molar ratio in spray solution (1:1, 1:2, and 1:3) and growth temperatures in the range of 400–600 °C. Scanning electron microscopy (SEM), X‐ray diffraction (XRD), energy dispersive X‐ray analysis (EDX), UV–VIS, and PL spectroscopy were applied to characterize the ZnS layers. Layers obtained at temperatures up to 450 °C are not well crystallized and contain residues originated from undecomposed precursors. ZnS films become crystalline at Ts = 500 °C. Layers grown from 1:1 solution at 550 °C are mixture of ZnS and ZnO phases, whereas at 600 °C layers of ZnO were obtained. Films produced from 1:2 solution at 500–600 °C are of ZnS with a wurtzite structure and Eg of 3.66 eV, but contain traces of ZnO phase when grown at 550 or 600 °C. Appearance of ZnO phase in the films grown from 1:1 and 1:2 solutions is explained by the res...
Photocatalysts synthesized by sol-gel method inevitably incorporate carbon together with dopants.... more Photocatalysts synthesized by sol-gel method inevitably incorporate carbon together with dopants. The objective of the research consists in the synthesis and testing of photocatalytic activity of car bon containing titanium dioxide photocatalysts calcinated at various temperatures. The optical and struc tural properties of the catalysts were also studied. The activity was tested in visible light in aqueous photocat alytic oxidation of three various type pollutants, methyl tert butyl ether, p toluidine and phenol, where the divergent character of the C-TiO 2 catalysts was distinctively observed: methyl tert butyl ether and p tolui dine were oxidized with the efficiency close to or even surpassing that of UV irradiated P25 (Evonik), whereas phenol was oxidized poorly. The observed photocatalytic activity, where quantum efficiency varied from 0.6 to 2.3 and from 0.1 to 1.2% for p toluidine and phenol degradation respectively, may be explained by the different electrostatic properties of the catalysts' surface and the tested substances, i.e. their interac tion. This compromises the widespread usage of phenol as a reference substance for comparison of catalytic activities of catalysts.
IOP Conference Series: Materials Science and Engineering, 2013
ZnO layers comprizing rods were deposited by chemical spray pyrolysis (CSP) method at 520 ˚C on d... more ZnO layers comprizing rods were deposited by chemical spray pyrolysis (CSP) method at 520 ˚C on different FTO (SnO2:F)/glass substrates using zinc chloride aqueous solutions. Substrates were purchased from different manufactures and differ by morphology, grain size and roughness of FTO electrode. FTO/glass substrates and ZnO layers grown on them were characterised with the help of XRD, AFM, high resolution SEM, EDX methods. The relationship between nanorod formation and substrate properties was studied. It was found that substrate roughness and grain size influence the ZnO rods formation. Deposition of rods (d=300 nm, L=1.4 μm) was successful on the FTO layers with grain sizes around 30-50 nm and roughness below 10 nm, whereas large-grained FTO (grain size > 130 nm) resulted in thick, lowaspect ratio crystals with diameter around 400 nm and length of about 400 nm.
Surface properties of spray and electrodeposited rods were studied and compared Influence of hy... more Surface properties of spray and electrodeposited rods were studied and compared Influence of hydroxyl groups on the surface of as-deposited ZnO rods was observed Higher amount of hydroxyl groups on electrodeposited rods makes surface hydrophilic Impact of hydroxyl groups of aged samples is shaded by contamination within time Wettability of sprayed samples didn't change significantly within storage time
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