Thin CuInS 2 light-absorbing layer prospective for the solar cell applications is modified by gol... more Thin CuInS 2 light-absorbing layer prospective for the solar cell applications is modified by gold nanoparticles. Theoretical and experimental possibilities of placement nanoparticles over or under the CuInS 2 coating were tested. It was revealed that placement of nanoparticles under the CuInS 2 layer is better in terms of spray pyrolysis technique. It results in more effective plasmon-enhanced light absorption in the CuInS 2 layer at the visible/near infrared 650-700 nm spectral range.
The current paper provides a comparison of impact wear and sliding wear properties of the hard PV... more The current paper provides a comparison of impact wear and sliding wear properties of the hard PVD single layer TiN and Ti(C,N), multilayer (Ti,Al)N and nanocomposite FiVIc® coatings, deposited onto plasma nitrided low-alloy 42CrMo4 steel. All of the coatings studied demonstrated a relatively high impact wear resistance at the low (10 4 ) and medium (10 5 ) numbers of impact, however, all the studied coatings vanished at the high number of impacts (10 6 ). The most extensive wear amongst the coatings during the sliding wear test was observed for the (Ti,Al)N coating, with FiVIc® showing the least extensive wear. The most extensive wear of the counterbody (hardened steel ball) was registered for the (Ti,Al)N coating, with the lowest wear for the FiVIc® and Ti(C,N) coatings. The wear mechanism of coatings was mild abrasion, accompanied by oxidation, and the wear mechanism of the counterbody was plastic deformation.
Lanthanide-doped organic and carbon aerogels were obtained based on the modified resorcinol-forma... more Lanthanide-doped organic and carbon aerogels were obtained based on the modified resorcinol-formaldehyde aerogel preparation procedure. The prepared materials were tested as catalysts for the Michael reaction. Organic aerogels were prepared by sol-gel polymerization of 2,6-dihydroxy-4-methylbenzoic acid (dHMBA) mixed with 5-methylresorcinol (MR) and formaldehyde. The resulting gels were doped with Ln(NO 3) 3 (Ln = Ce, La, Nd, Pr) by ion-exchange and further dried with supercritical CO 2. Pyrolysis of organic aerogels at 900°C in N 2 atmosphere resulted in metal-doped carbon aerogels. The mostly mesoporous materials contained up to 12 wt.% of metal in organic aerogels and 22 wt.% in carbon aerogels. The materials were amorphous and crystal structures were not formed during pyrolysis. Ln-doped aerogels were tested as catalysts for Michael addition reaction. Organic aerogels doped with different lanthanides catalyze the Michael reaction efficiently with conversions ranging between 82 and 97% in 24 h. For Ln-doped carbon aerogels the conversion was modest (32%) to high (92%).
We report room-temperature ferromagnetism in Ca and Mg stabilized zirconia bulk samples and thin ... more We report room-temperature ferromagnetism in Ca and Mg stabilized zirconia bulk samples and thin films. Powders were prepared by the citrate-combustion route, and thin films grown on silicon substrates by the pulsed laser deposition technique. X-ray diffractograms and Raman spectra at room temperature reveal the formation of cubic phase zirconia. The observed ferromagnetism is robust at room temperature in both bulk as well as in thin film samples, although it is weaker in thin films. The origin of the ferromagnetism can be related to oxygen vacancies created due to divalent (calcium and magnesium) substitution for tetravalent zirconium ions.
In this study, TiO2 thin films were deposited by ultrasonic spray pyrolysis from solutions with c... more In this study, TiO2 thin films were deposited by ultrasonic spray pyrolysis from solutions with concentrations of 0.1 and 0.2 M. The deposition temperature was adjusted at 350 °C and all samples were annealed at 500 °C for 1 h in air. The thickness of TiO2 films was changed in the range of 50 to ca. 800 nm by varying the number of spray cycles from 1 to 21 and the solution concentration. The results showed that the mean crystallite size of the anatase structure, the surface roughness, and light absorption increased with the film thickness. The effect of film thickness on the photocatalytic activity was investigated with the photodegradation of stearic acid under UV-A irradiation. The optimal thickness of TiO2 films fabricated by ultrasonic spray pyrolysis for photocatalytic self-cleaning applications was in the range of 170–230 nm, indicating a ca. 2.6 times-higher photocatalytic self-cleaning activity compared to the reference sample, Pilkington ActivTM. The photocatalytic results ...
TiO2 thin films, modified by acetylacetone (AcacH) in solution, were deposited on glass substrate... more TiO2 thin films, modified by acetylacetone (AcacH) in solution, were deposited on glass substrate by ultrasonic spray pyrolysis and tested for photocatalytic activity in a multi-section continuous flow reactor by degradation of acetone and acetaldehyde under ultraviolet and visible light. The increase in molar ratio of AcacH in respect of titanium (IV) isopropoxide (TTIP) from 1:5 to 1:8 modified the electronic structure of the films, favoring enhanced photocatalytic activity. The photocatalytic activity was enhanced approximately twofold on the film with molar ratio 1:8 under both irradiations; the film completely oxidized 10 ppm of acetone and acetaldehyde. The photocatalytic efficacy of TiO2 films in oxidation of air pollutants was three times higher compared to the industrial glass Pilkington ActivTM. Moreover, all the synthesized films indicate antibacterial efficiency against E. coli of over 99% under ultraviolet. TiO2 film, with TTIP:AcacH molar ratio 1:8 having great possibi...
Preparation of electrocatalysts often relies on the use of multiple starting materials, with exam... more Preparation of electrocatalysts often relies on the use of multiple starting materials, with examples arising from a single precursor being less common. We have surveyed a series of heterobivalent scaffolds to identify an iron/benzimidazole-based metal−organic framework as a uniform starting material. By merging the catechol and imidazole units together, we get a direct entry into a highly efficient bifunctional oxygen electrocatalyst, which alleviates the need for dopants and modifying conditions. We demonstrate that by fine-tuning the chemical nature of an organic linker, one is able to modulate the electrochemical properties of a single precursor-derived electrocatalyst material.
Solution-processed metal oxides require a great deal of thermal budget in order to achieve the de... more Solution-processed metal oxides require a great deal of thermal budget in order to achieve the desired film properties. Here, we show that the deposition temperature of sprayed zirconium oxide (ZrOx) thin film can be lowered by exposing the film surface to an ultraviolet (UV) ozone treatment at room temperature. Atomic force microscopy reveals a smooth and uniform film with the root mean square roughness reduced from ~ 0.63 nm (UVO-O) to ~ 0.28 nm (UVO-120) in the UV–ozone treated ZrOx films. X-ray photoelectron spectroscopy analysis indicates the formation of a Zr–O network on the surface film, and oxygen vacancy is reduced in the ZrOx lattice by increasing the UV–ozone treatment time. The leakage current density in Al/ZrOx/p-Si structure was reduced by three orders of magnitude by increasing the UV-ozone exposure time, while the capacitance was in the range 290–266 nF/cm2, corresponding to a relative permittivity (k) in the range 5.8–6.6 at 1 kHz. An indium gallium zinc oxide (IGZ...
Owing to its high conductivity, graphene has been incorporated into polymeric nanofibers to creat... more Owing to its high conductivity, graphene has been incorporated into polymeric nanofibers to create advanced materials for flexible electronics, sensors and tissue engineering. Typically, these graphenebased nanofibers are prepared by electrospinning synthetic polymers, whereas electrospun graphenebiopolymer nanofibers have been rarely reported due to the poor compatibility of graphene with biopolymers. Herein, we report a new method for the preparation of graphene-biopolymer nanofibers using the judicious combination of an ionic liquid and electrospinning. Cellulose acetate (CA) has been used as the biopolymer, graphene oxide (GO) nanoparticles as the source of graphene and 1-butyl-3methylimidazolium chloride ([BMIM]Cl) as the ionic liquid (IL) to create CA-[BMIM]Cl-GO nanofibers by electrospinning for the first time. Moreover, we developed a new route to convert CA-[BMIM]Cl-GO nanofibers to reduced GO nanofibers using hydrazine vapor under ambient conditions to enhance the conductivity of the hybrid nanofibers. The graphene sheets were shown to be uniformly *
Herein we present a comparative study on highly transparent, conductive aluminium-doped ZnO (AZO)... more Herein we present a comparative study on highly transparent, conductive aluminium-doped ZnO (AZO) thin films deposited by pneumatic spray pyrolysis (PSP) of a zinc acetate based solution and a zinc acetylacetonate based solution on soda lime glass. The structural, optical and electrical properties of the films were studied depending on aluminium content in the precursor solution and substrate temperature during deposition (Ts). The solution used to prepare AZO thin films contained 0.2 M zinc acetate or 0.2 M zinc acetylacetonate and aluminium acetylacetonate between 0–15 at.% [Al]/[Zn]. Substrate temperature was varied from 275 to 450 °C. Transmittance and reflectance spectra were recorded by UV-VIS-NIR spectroscopy. Resistivity, mobility and charge carrier density were determined by four point probe measurements in ambient conditions. According to X-ray diffraction analysis, AZO films are highly c-axis oriented until 2–3 at.% [Al]/[Zn] in the spray solution, depending on zinc precu...
Chemical spray pyrolysis (CSP) is a fast wet-chemical deposition method in which an aerosol is gu... more Chemical spray pyrolysis (CSP) is a fast wet-chemical deposition method in which an aerosol is guided by carrier gas onto a hot substrate where the decomposition of the precursor chemicals occurs. The aerosol is produced using an ultrasonic oscillator in a bath of precursor solution and guided by compressed air. The use of the ultrasonic CSP resulted in the growth of homogeneous and well-adhered layers that consist of submicron crystals of single-phase Sb2S3 with a bandgap of 1.6 eV if an abundance of sulfur source is present in the precursor solution (SbCl3/SC(NH2)2 = 1:6) sprayed onto the substrate at 250 °C in air. Solar cells with glass-ITO-TiO2-Sb2S3-P3HT-Au structure and an active area of 1 cm2 had an open circuit voltage of 630 mV, short circuit current density of 5 mA/cm2, a fill factor of 42% and a conversion efficiency of 1.3%. Conversion efficiencies up to 1.9% were obtained from solar cells with smaller areas.
Acetylacetone is used as a chelating agent for titanium(IV) isopropoxide to inhibit hydrolysis an... more Acetylacetone is used as a chelating agent for titanium(IV) isopropoxide to inhibit hydrolysis and stabilize the precursor solution. The effect of the molar ratio between titanium(IV) isopropoxide and acetylacetone of 1:1, 1:2, 1:3 and 1:4 in the precursor solution on the morphological, structural and optical properties of TiO 2 thin film was investigated. These properties were studied using Fourier transformed infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, X-ray diffraction and UV-vis spectroscopy as a function of the molar ratios for the as-deposited thin films and films annealed at temperatures of 700, 800 and 950°C. Mixed anatase and rutile phases were detected after annealing at 800°C for 1:1 and 1:2 molar ratios and at 700°C for 1:3 and 1:4 molar ratios. The optical band gap decreased from 3.45 to 3.02 eV with an increase in the annealing temperature in agreement with corresponding structural changes.
The chemical spray pyrolysis method was used to deposit CuInS2 (CIS) thin films and Au nanopartic... more The chemical spray pyrolysis method was used to deposit CuInS2 (CIS) thin films and Au nanoparticles (NPs) in two configurations: glass/Au-NP layer covered with CuInS2 film (Au-NP/CIS) and glass/CuInS2 films covered with Au-NP layer (CIS/Au-NP). According to X-ray diffraction (XRD), the spray of 2 mM HAuCl4 aqueous solution with a volume of 2.5 to 15 ml onto a glass substrate at 340°C results in metallic Au nanoparticles with a similar mean crystallite size in the range of 30 - 38 nm. The mean crystallite sizes remain in the range of 15 - 20 nm when grown onto a CIS film. The prepared films show plasmonic light absorption with increasing intensity in the spectral range of 500- 800 nm when increasing the volume of HAuCl4 solution sprayed. When compared to bare CIS on glass, the absorptance was increased ca. 4.5 times in the case of glass/Au-NP/CIS and ca. 3 times in the case of glass/CIS/Au-NP configuration. The glass/Au-NP/CIS configuration had an advantage since Au-NP could be embe...
The effect of post-deposition annealing in flowing H 2 S atmosphere at 530-C on the properties of... more The effect of post-deposition annealing in flowing H 2 S atmosphere at 530-C on the properties of sprayed CuInS 2 (CIS) thin films was studied. The structure and composition were characterized by XRD, SEM and EDX. The density of carriers was obtained from C-V measurements of CIS/ Al Schottky barriers at room temperature (RT), the resistivity was measured at RT and as a function of temperature. H 2 S annealing eliminates the deficiency of sulfur and results in closely stoichiometric, well-crystallized films of CuInS 2. Annealed films are consisting of grains with a size up to 300 nm. By treatment, the optical band gap increases from 1.44 to 1.49 eV as determined from absorbance spectra. The electrical properties are depending on the cooling rates. The specific resistivity of 10 7 and 10 5 V cm and carrier concentrations in the order of 10 14 and 10 17 cm À 3 are characteristics of rapidly and slowly cooled films, respectively. Pronounced parabolic behaviour of the lnr vs. 1/T plot of rapidly cooled samples shows that grain boundaries effect should be considered in the conductivity mechanism. Slow cooling favours the removal of a resistive phase from the grain boundaries and the film conductivity increases. The different predominating defects are assumed to be present in the rapidly and slowly cooled films. The conductivity thermal activation energies of 80 and 160 meV are characteristic of slowly cooled samples deposited from ''stoichiometric'' or ''Cu-rich'' solutions, respectively. It shows that not only the treatment conditions but also the film deposition parameters are highly important in the development of the material properties.
CuInS 2 films were deposited by spray pyrolysis method at 250 ºC and 350 ºC using aqueous solutio... more CuInS 2 films were deposited by spray pyrolysis method at 250 ºC and 350 ºC using aqueous solutions of CuCl 2 , InCl 3 and SC(NH 2) 2 at molar ratio of precursors Cu:In:S=1:1:3 in spray solution. Films were characterized by X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) techniques. According to XPS, the films grown at 350 ºC have Cu 2+ containing pieces on the surface, the film composition in bulk region is not homogeneous and contains metal bonded oxygen in amount of 5-8 at.%. Deposition at 250 °C reduces the content of oxygen down to ~ 1 at. %, the films are low-crystalline with uniform distribution of the elements throughout the film and contain some excess of sulfur compared to stoichiometric CuInS 2 .
Solar cells consisting of an extremely thin In2S3/CuInS2 buffer/absorber layer uniformly covering... more Solar cells consisting of an extremely thin In2S3/CuInS2 buffer/absorber layer uniformly covering planar ZnO were prepared entirely by chemical spray pyrolysis. Au nanoparticles (Au-NPs) were formed via thermal decomposition of a gold(III) chloride trihydrate (HAuCl4·3H2O) precursor by spraying 2 mmol/L of the aqueous precursor solution onto a substrate held at 260 °C. Current–voltage scans and external quantum efficiency spectra were used to evaluate the solar cell performance. This work investigates the effect of the location of the Au-NP layer deposition (front side vs rear side) in the solar cell and the effect of varying the volume (2.5–10 mL) of the sprayed Au precursor solution. A 63% increase (from 4.6 to 7.5 mA/cm2) of the short-circuit current density was observed when 2.5 mL of the precursor solution was deposited onto the rear side of the solar cell.
TiO2 thin films were prepared by spray pyrolysis method. The solution containing titanium(IV)isop... more TiO2 thin films were prepared by spray pyrolysis method. The solution containing titanium(IV)isopropoxide, acetylacetone and ethanol was deposited onto n-type Si(100) and HD Si(100) wafers at substrate temperatures of 315 to 500 0C by pulsed spray solution feed. The films were characterized by FTIR, XRD, AFM, ellipsometry, impedance and I-V measurements. Asdeposited films prepared below 500 0C were amorphous, whereas crystalline films could be achieved at 500 0C. Subsequent annealing at 700 °C in air led to crystalline anatase formation for films deposited below 400 °C. Rutile phase appears in annealed films prepared at a growth temperature above 400 °C. Anatase TiO2 films show refractive index in the range 2.20 to 2.40 and exhibit a relative dielectric constant value of 75 in the range 1 to 100 kHz. Electric breakdown occurs for 120 nm thick film at 250 kV/cm.
Thin CuInS 2 light-absorbing layer prospective for the solar cell applications is modified by gol... more Thin CuInS 2 light-absorbing layer prospective for the solar cell applications is modified by gold nanoparticles. Theoretical and experimental possibilities of placement nanoparticles over or under the CuInS 2 coating were tested. It was revealed that placement of nanoparticles under the CuInS 2 layer is better in terms of spray pyrolysis technique. It results in more effective plasmon-enhanced light absorption in the CuInS 2 layer at the visible/near infrared 650-700 nm spectral range.
The current paper provides a comparison of impact wear and sliding wear properties of the hard PV... more The current paper provides a comparison of impact wear and sliding wear properties of the hard PVD single layer TiN and Ti(C,N), multilayer (Ti,Al)N and nanocomposite FiVIc® coatings, deposited onto plasma nitrided low-alloy 42CrMo4 steel. All of the coatings studied demonstrated a relatively high impact wear resistance at the low (10 4 ) and medium (10 5 ) numbers of impact, however, all the studied coatings vanished at the high number of impacts (10 6 ). The most extensive wear amongst the coatings during the sliding wear test was observed for the (Ti,Al)N coating, with FiVIc® showing the least extensive wear. The most extensive wear of the counterbody (hardened steel ball) was registered for the (Ti,Al)N coating, with the lowest wear for the FiVIc® and Ti(C,N) coatings. The wear mechanism of coatings was mild abrasion, accompanied by oxidation, and the wear mechanism of the counterbody was plastic deformation.
Lanthanide-doped organic and carbon aerogels were obtained based on the modified resorcinol-forma... more Lanthanide-doped organic and carbon aerogels were obtained based on the modified resorcinol-formaldehyde aerogel preparation procedure. The prepared materials were tested as catalysts for the Michael reaction. Organic aerogels were prepared by sol-gel polymerization of 2,6-dihydroxy-4-methylbenzoic acid (dHMBA) mixed with 5-methylresorcinol (MR) and formaldehyde. The resulting gels were doped with Ln(NO 3) 3 (Ln = Ce, La, Nd, Pr) by ion-exchange and further dried with supercritical CO 2. Pyrolysis of organic aerogels at 900°C in N 2 atmosphere resulted in metal-doped carbon aerogels. The mostly mesoporous materials contained up to 12 wt.% of metal in organic aerogels and 22 wt.% in carbon aerogels. The materials were amorphous and crystal structures were not formed during pyrolysis. Ln-doped aerogels were tested as catalysts for Michael addition reaction. Organic aerogels doped with different lanthanides catalyze the Michael reaction efficiently with conversions ranging between 82 and 97% in 24 h. For Ln-doped carbon aerogels the conversion was modest (32%) to high (92%).
We report room-temperature ferromagnetism in Ca and Mg stabilized zirconia bulk samples and thin ... more We report room-temperature ferromagnetism in Ca and Mg stabilized zirconia bulk samples and thin films. Powders were prepared by the citrate-combustion route, and thin films grown on silicon substrates by the pulsed laser deposition technique. X-ray diffractograms and Raman spectra at room temperature reveal the formation of cubic phase zirconia. The observed ferromagnetism is robust at room temperature in both bulk as well as in thin film samples, although it is weaker in thin films. The origin of the ferromagnetism can be related to oxygen vacancies created due to divalent (calcium and magnesium) substitution for tetravalent zirconium ions.
In this study, TiO2 thin films were deposited by ultrasonic spray pyrolysis from solutions with c... more In this study, TiO2 thin films were deposited by ultrasonic spray pyrolysis from solutions with concentrations of 0.1 and 0.2 M. The deposition temperature was adjusted at 350 °C and all samples were annealed at 500 °C for 1 h in air. The thickness of TiO2 films was changed in the range of 50 to ca. 800 nm by varying the number of spray cycles from 1 to 21 and the solution concentration. The results showed that the mean crystallite size of the anatase structure, the surface roughness, and light absorption increased with the film thickness. The effect of film thickness on the photocatalytic activity was investigated with the photodegradation of stearic acid under UV-A irradiation. The optimal thickness of TiO2 films fabricated by ultrasonic spray pyrolysis for photocatalytic self-cleaning applications was in the range of 170–230 nm, indicating a ca. 2.6 times-higher photocatalytic self-cleaning activity compared to the reference sample, Pilkington ActivTM. The photocatalytic results ...
TiO2 thin films, modified by acetylacetone (AcacH) in solution, were deposited on glass substrate... more TiO2 thin films, modified by acetylacetone (AcacH) in solution, were deposited on glass substrate by ultrasonic spray pyrolysis and tested for photocatalytic activity in a multi-section continuous flow reactor by degradation of acetone and acetaldehyde under ultraviolet and visible light. The increase in molar ratio of AcacH in respect of titanium (IV) isopropoxide (TTIP) from 1:5 to 1:8 modified the electronic structure of the films, favoring enhanced photocatalytic activity. The photocatalytic activity was enhanced approximately twofold on the film with molar ratio 1:8 under both irradiations; the film completely oxidized 10 ppm of acetone and acetaldehyde. The photocatalytic efficacy of TiO2 films in oxidation of air pollutants was three times higher compared to the industrial glass Pilkington ActivTM. Moreover, all the synthesized films indicate antibacterial efficiency against E. coli of over 99% under ultraviolet. TiO2 film, with TTIP:AcacH molar ratio 1:8 having great possibi...
Preparation of electrocatalysts often relies on the use of multiple starting materials, with exam... more Preparation of electrocatalysts often relies on the use of multiple starting materials, with examples arising from a single precursor being less common. We have surveyed a series of heterobivalent scaffolds to identify an iron/benzimidazole-based metal−organic framework as a uniform starting material. By merging the catechol and imidazole units together, we get a direct entry into a highly efficient bifunctional oxygen electrocatalyst, which alleviates the need for dopants and modifying conditions. We demonstrate that by fine-tuning the chemical nature of an organic linker, one is able to modulate the electrochemical properties of a single precursor-derived electrocatalyst material.
Solution-processed metal oxides require a great deal of thermal budget in order to achieve the de... more Solution-processed metal oxides require a great deal of thermal budget in order to achieve the desired film properties. Here, we show that the deposition temperature of sprayed zirconium oxide (ZrOx) thin film can be lowered by exposing the film surface to an ultraviolet (UV) ozone treatment at room temperature. Atomic force microscopy reveals a smooth and uniform film with the root mean square roughness reduced from ~ 0.63 nm (UVO-O) to ~ 0.28 nm (UVO-120) in the UV–ozone treated ZrOx films. X-ray photoelectron spectroscopy analysis indicates the formation of a Zr–O network on the surface film, and oxygen vacancy is reduced in the ZrOx lattice by increasing the UV–ozone treatment time. The leakage current density in Al/ZrOx/p-Si structure was reduced by three orders of magnitude by increasing the UV-ozone exposure time, while the capacitance was in the range 290–266 nF/cm2, corresponding to a relative permittivity (k) in the range 5.8–6.6 at 1 kHz. An indium gallium zinc oxide (IGZ...
Owing to its high conductivity, graphene has been incorporated into polymeric nanofibers to creat... more Owing to its high conductivity, graphene has been incorporated into polymeric nanofibers to create advanced materials for flexible electronics, sensors and tissue engineering. Typically, these graphenebased nanofibers are prepared by electrospinning synthetic polymers, whereas electrospun graphenebiopolymer nanofibers have been rarely reported due to the poor compatibility of graphene with biopolymers. Herein, we report a new method for the preparation of graphene-biopolymer nanofibers using the judicious combination of an ionic liquid and electrospinning. Cellulose acetate (CA) has been used as the biopolymer, graphene oxide (GO) nanoparticles as the source of graphene and 1-butyl-3methylimidazolium chloride ([BMIM]Cl) as the ionic liquid (IL) to create CA-[BMIM]Cl-GO nanofibers by electrospinning for the first time. Moreover, we developed a new route to convert CA-[BMIM]Cl-GO nanofibers to reduced GO nanofibers using hydrazine vapor under ambient conditions to enhance the conductivity of the hybrid nanofibers. The graphene sheets were shown to be uniformly *
Herein we present a comparative study on highly transparent, conductive aluminium-doped ZnO (AZO)... more Herein we present a comparative study on highly transparent, conductive aluminium-doped ZnO (AZO) thin films deposited by pneumatic spray pyrolysis (PSP) of a zinc acetate based solution and a zinc acetylacetonate based solution on soda lime glass. The structural, optical and electrical properties of the films were studied depending on aluminium content in the precursor solution and substrate temperature during deposition (Ts). The solution used to prepare AZO thin films contained 0.2 M zinc acetate or 0.2 M zinc acetylacetonate and aluminium acetylacetonate between 0–15 at.% [Al]/[Zn]. Substrate temperature was varied from 275 to 450 °C. Transmittance and reflectance spectra were recorded by UV-VIS-NIR spectroscopy. Resistivity, mobility and charge carrier density were determined by four point probe measurements in ambient conditions. According to X-ray diffraction analysis, AZO films are highly c-axis oriented until 2–3 at.% [Al]/[Zn] in the spray solution, depending on zinc precu...
Chemical spray pyrolysis (CSP) is a fast wet-chemical deposition method in which an aerosol is gu... more Chemical spray pyrolysis (CSP) is a fast wet-chemical deposition method in which an aerosol is guided by carrier gas onto a hot substrate where the decomposition of the precursor chemicals occurs. The aerosol is produced using an ultrasonic oscillator in a bath of precursor solution and guided by compressed air. The use of the ultrasonic CSP resulted in the growth of homogeneous and well-adhered layers that consist of submicron crystals of single-phase Sb2S3 with a bandgap of 1.6 eV if an abundance of sulfur source is present in the precursor solution (SbCl3/SC(NH2)2 = 1:6) sprayed onto the substrate at 250 °C in air. Solar cells with glass-ITO-TiO2-Sb2S3-P3HT-Au structure and an active area of 1 cm2 had an open circuit voltage of 630 mV, short circuit current density of 5 mA/cm2, a fill factor of 42% and a conversion efficiency of 1.3%. Conversion efficiencies up to 1.9% were obtained from solar cells with smaller areas.
Acetylacetone is used as a chelating agent for titanium(IV) isopropoxide to inhibit hydrolysis an... more Acetylacetone is used as a chelating agent for titanium(IV) isopropoxide to inhibit hydrolysis and stabilize the precursor solution. The effect of the molar ratio between titanium(IV) isopropoxide and acetylacetone of 1:1, 1:2, 1:3 and 1:4 in the precursor solution on the morphological, structural and optical properties of TiO 2 thin film was investigated. These properties were studied using Fourier transformed infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, X-ray diffraction and UV-vis spectroscopy as a function of the molar ratios for the as-deposited thin films and films annealed at temperatures of 700, 800 and 950°C. Mixed anatase and rutile phases were detected after annealing at 800°C for 1:1 and 1:2 molar ratios and at 700°C for 1:3 and 1:4 molar ratios. The optical band gap decreased from 3.45 to 3.02 eV with an increase in the annealing temperature in agreement with corresponding structural changes.
The chemical spray pyrolysis method was used to deposit CuInS2 (CIS) thin films and Au nanopartic... more The chemical spray pyrolysis method was used to deposit CuInS2 (CIS) thin films and Au nanoparticles (NPs) in two configurations: glass/Au-NP layer covered with CuInS2 film (Au-NP/CIS) and glass/CuInS2 films covered with Au-NP layer (CIS/Au-NP). According to X-ray diffraction (XRD), the spray of 2 mM HAuCl4 aqueous solution with a volume of 2.5 to 15 ml onto a glass substrate at 340°C results in metallic Au nanoparticles with a similar mean crystallite size in the range of 30 - 38 nm. The mean crystallite sizes remain in the range of 15 - 20 nm when grown onto a CIS film. The prepared films show plasmonic light absorption with increasing intensity in the spectral range of 500- 800 nm when increasing the volume of HAuCl4 solution sprayed. When compared to bare CIS on glass, the absorptance was increased ca. 4.5 times in the case of glass/Au-NP/CIS and ca. 3 times in the case of glass/CIS/Au-NP configuration. The glass/Au-NP/CIS configuration had an advantage since Au-NP could be embe...
The effect of post-deposition annealing in flowing H 2 S atmosphere at 530-C on the properties of... more The effect of post-deposition annealing in flowing H 2 S atmosphere at 530-C on the properties of sprayed CuInS 2 (CIS) thin films was studied. The structure and composition were characterized by XRD, SEM and EDX. The density of carriers was obtained from C-V measurements of CIS/ Al Schottky barriers at room temperature (RT), the resistivity was measured at RT and as a function of temperature. H 2 S annealing eliminates the deficiency of sulfur and results in closely stoichiometric, well-crystallized films of CuInS 2. Annealed films are consisting of grains with a size up to 300 nm. By treatment, the optical band gap increases from 1.44 to 1.49 eV as determined from absorbance spectra. The electrical properties are depending on the cooling rates. The specific resistivity of 10 7 and 10 5 V cm and carrier concentrations in the order of 10 14 and 10 17 cm À 3 are characteristics of rapidly and slowly cooled films, respectively. Pronounced parabolic behaviour of the lnr vs. 1/T plot of rapidly cooled samples shows that grain boundaries effect should be considered in the conductivity mechanism. Slow cooling favours the removal of a resistive phase from the grain boundaries and the film conductivity increases. The different predominating defects are assumed to be present in the rapidly and slowly cooled films. The conductivity thermal activation energies of 80 and 160 meV are characteristic of slowly cooled samples deposited from ''stoichiometric'' or ''Cu-rich'' solutions, respectively. It shows that not only the treatment conditions but also the film deposition parameters are highly important in the development of the material properties.
CuInS 2 films were deposited by spray pyrolysis method at 250 ºC and 350 ºC using aqueous solutio... more CuInS 2 films were deposited by spray pyrolysis method at 250 ºC and 350 ºC using aqueous solutions of CuCl 2 , InCl 3 and SC(NH 2) 2 at molar ratio of precursors Cu:In:S=1:1:3 in spray solution. Films were characterized by X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) techniques. According to XPS, the films grown at 350 ºC have Cu 2+ containing pieces on the surface, the film composition in bulk region is not homogeneous and contains metal bonded oxygen in amount of 5-8 at.%. Deposition at 250 °C reduces the content of oxygen down to ~ 1 at. %, the films are low-crystalline with uniform distribution of the elements throughout the film and contain some excess of sulfur compared to stoichiometric CuInS 2 .
Solar cells consisting of an extremely thin In2S3/CuInS2 buffer/absorber layer uniformly covering... more Solar cells consisting of an extremely thin In2S3/CuInS2 buffer/absorber layer uniformly covering planar ZnO were prepared entirely by chemical spray pyrolysis. Au nanoparticles (Au-NPs) were formed via thermal decomposition of a gold(III) chloride trihydrate (HAuCl4·3H2O) precursor by spraying 2 mmol/L of the aqueous precursor solution onto a substrate held at 260 °C. Current–voltage scans and external quantum efficiency spectra were used to evaluate the solar cell performance. This work investigates the effect of the location of the Au-NP layer deposition (front side vs rear side) in the solar cell and the effect of varying the volume (2.5–10 mL) of the sprayed Au precursor solution. A 63% increase (from 4.6 to 7.5 mA/cm2) of the short-circuit current density was observed when 2.5 mL of the precursor solution was deposited onto the rear side of the solar cell.
TiO2 thin films were prepared by spray pyrolysis method. The solution containing titanium(IV)isop... more TiO2 thin films were prepared by spray pyrolysis method. The solution containing titanium(IV)isopropoxide, acetylacetone and ethanol was deposited onto n-type Si(100) and HD Si(100) wafers at substrate temperatures of 315 to 500 0C by pulsed spray solution feed. The films were characterized by FTIR, XRD, AFM, ellipsometry, impedance and I-V measurements. Asdeposited films prepared below 500 0C were amorphous, whereas crystalline films could be achieved at 500 0C. Subsequent annealing at 700 °C in air led to crystalline anatase formation for films deposited below 400 °C. Rutile phase appears in annealed films prepared at a growth temperature above 400 °C. Anatase TiO2 films show refractive index in the range 2.20 to 2.40 and exhibit a relative dielectric constant value of 75 in the range 1 to 100 kHz. Electric breakdown occurs for 120 nm thick film at 250 kV/cm.
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Papers by Arvo Mere