High Band Gap Nanocrystalline Tungsten Carbide (nc-WC) Thin Films Grown by Hot Wire Chemical Vapor Deposition (HW-CVD) Method

In present study nanocrystalline tungsten carbide (nc-WC) thin films were deposited by HW-CVD using heated W filament and CF4 gas. Influence of CF4 flow rate on structural, optical and electrical properties has been investigated. Formation of WC thin films was confirmed by low angle XRD, Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) analysis. Low angle XRD analysis revealed that WC crystallites have preferred orientation in (101) direction and with increase in CF4 flow rate the volume fraction of WC crystallites and its average grain size increases. Formation of nano-sized WC was also confirmed by transmission electron microscopy (TEM) analysis. UV-Visible spectroscopy analysis revealed increase in optical transmission with increase in CF4 flow rate. The WC film deposited for 40 sccm of CF4 flow rate show high transparency (- 80-85 %) ranging from visible to infrared wavelengths region. The band gap shows increasing trend with increase in CF4 flow rate (3.48-4.18 eV). The electrical conductivity measured using Hall Effect was found in the range - 103-141 S/cm over the entire range of CF4 flow rate studied. The obtained results suggest that these wide band gap and conducting nc-WC films can be used as low cost counter electrodes in DSSCs and co-catalyst in electrochemical water splitting for hydrogen production

Synthesis and characterization of molybdenum back contact using direct current-magnetron sputtering for thin film solar cells

In present work, we report synthesis of molybdenum (Mo) thin films by direct current (DC)-magnetron sputtering method. The structural, optical, morphological, and electrical properties were investigated as a function of target-to-substrate distance. From the results, it is evident that with increase in target-to-substrate distance the thickness of films decreases while its sheet resistance and electrical resistivity increases, which is confirmed by van der Pauw method. Low angle XRD analysis revealed that with increase in target-to-substrate distance preferred orientation of Mo crystallites changes from (211) to (110) and its size decreases. The field emission scanning electron microscope (FE-SEM) analysis revealed a significant change in surface morphology with increase in target-to-substrate distance. UV-Visible spectroscopy analysis showed that Mo films deposited at higher target-to-substrate distance have more reflection than those deposited at lower target-to-substrate. Finally, adhesion test was performed using scotch hatch tape adhesion test which show all Mo films have excellent adhesion over the entire range of target-to-substrate distance studied. The employment of such Mo films as back contact can be useful to improve efficiency of CZTS solar cells

Effect of bath temperature on optical and morphology properties of CdS thin films grown by chemical bath deposition

Synthesis of CdS thin films were carried out onto glass substrates by chemical bath deposition (CBD) method using CdCl2asCd2+ and thiourea as S2-ion source with ammonia as a complexing agent. Influence of bath temperature on structural,morphology and optical properties has been systematically and carefully investigated. XRD analysis revealed that the synthesizedCdS films are nanocrystalline having hexagonal structure with (002) preferential orientation. Estimated crystallite size was foundin the range 16-32 nm. The UV-Visible spectroscopy analysis showed that the films have high transmission (> 70%) in visibleand NIR region of solar spectrum. Optical band gap was found > 2.3 eV over the entire range of bath temperature studied. TheRaman spectra for the CdS films deposited at various bath temperatures shows a continuous shift of 1 LO phonon peak towardshigher frequency which suggest the improvement of structural order with increase in bath temperature. The increase in theintensity ratio, 2LO/1LO with bath temperature indicates enhancement of crystallinity of CdS films with increase in bathtemperature. The SEM analysis showed that CdS films deposited at various bath temperatures are smooth, homogeneous, andnearly uniform with randomly oriented spherical nanocrystallites

Electrodeposition of template free hierarchical ZnO nanorod arrays via a chloride medium

We have successfully grown template and buffer free ZnO nanorod films via chloride medium by controlling bath temperature in a simple and cost effective electrochemical deposition method. Thin films of ZnO nano-rods were obtained by applying a potential of −0.75 V by employing Ag/AgCl reference electrode for 4 h of deposition time. The CV measurements were carried out to determine potential required to deposit ZnO nanorod films whereas chronoamperometry studies were carried out to investigate current and time required to deposit ZnO nanorod films. The formation of ZnO nanorod has been confirmed by scanning electron microscopy (SEM) and Raman spectroscopy. Low angle XRD analysis confirms that ZnO nanorod films have preferred orientation along (101) direction with hexagonal wurtzite crystal structure. The SEM micrographs show nice surface morphology with uniform, dense and highly crystalline hexagonal ZnO nanorods formation. Bath temperature has a little influence on the orientation of nanorods but has a great impact on their aspect ratio. Increase in bath temperature show improvement in crystallinity, increase in diameter and uniform distribution of nanorods. Compositional analysis shows that the amount of oxygen is ~49.35 % and that of Zn is ~50.65 %. The optical band gap values were found to be 3.19 and 3.26 eV for ZnO nanorods prepared at bath temperature 70 and 80 °C respectively. These results indicate that by controlling the bath temperature band gap of ZnO nanorods can be tailored. The obtained results suggest that it is possible to synthesize ZnO nanorod films by a simple, cost effective electrodeposition process which can be useful for opto-electronic devices fabrication

Магнетронне розпилення при постійному тоці зворотного контакту Mo для тонкоплівкових сонячних елементів з халькопіриту

In present work, Mo films were deposited on corning glass substrates using DC-Magnetron sputtering. Influence of DC sputtering power on electrical, structural, morphological, optical and topological properties has been investigated by using Hall effect, Х-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-Visible spectroscopy, non-contact-atomic force microscopy (NC-AFM) etc. It is observed that electrical resistivity and adhesion of Mo thin film were strongly affected by DC power. The synthesized Mo films were of few micrometer thicknesses (~ 0.9-1.6 m) with deposition rate in the range of 32-57 nm/min. Cross-hatch cut and Scotch tape adhesion test showed that all Mo films have good adhesion to the substrate. XRD analysis showed that as-deposited Mo films have preferred orientation in (110) direction and with enhancement in its crystallinity and average grain size with an increase in the DC sputtering power. Furthermore, XRD analysis showed that the Mo films deposited at DC sputtering power 300 W exhibit tensile strain, while deposited at DC sputtering power 350 W – exhibit compressive strain. FE-SEM analysis showed that all Mo films are dense, homogeneous and free of flaws and cracks. In the visible range of the spectrum, an increase in an average reflection of Mo films with DC sputtering power was observed by UV-Visible spectroscopy analysis. NC-AFM characterization revealed that the surface roughness of the films increases with an increase in the DC sputtering power. Hall effect measurements showed that the electrical resistivity of Mo films decreases while charge carrier mobility show increasing trend with increase in DC sputtering power. The obtained results suggest that as-synthesized Mo thin films with DC power 300 W have potential application as a back contact material for chalcopyrite compounds based on solar cells due to good adhesion and low electrical resistivity.В даній роботі, плівки Mo осаджувалися на підкладках із скла з використанням магнетронного розпилення при постійному струмі. Досліджено вплив потужності розпилення на електричні, структурні, морфологічні, оптичні та топологічні властивості за допомогою ефекту Холла, рентгенівської дифракції, автоелектронної скануючої мікроскопії, спектроскопії в УФ та видимої областях, неконтактної атомно-силової мікроскопії, тощо. Виявлено, що потужність постійного струму суттєво впливає на електричний опір і адгезію тонкої плівки Мо. Синтезовані плівки Mo мали товщину декількох мікрометрів (~ 0.9-1.6 мкм) зі швидкістю осадження в діапазоні 32-57 нм/хв. Випробування показали, що всі плівки Mo мають гарну адгезію до підкладки. Рентгено-дифракційний аналіз показав, що свіжосконденсовані плівки Mo мають переважну орієнтацію (110) і поліпшення її кристалічності та середнього розміру зерна зі збільшенням потужності розпилення при постійному струмі. Крім того, рентгенодифракційний аналіз показав, що плівки Mo, нанесені при потужності розпилення 300 Вт, демонструють деформацію розтягування, в той час як нанесені при потужності розпилення 350 Вт демонструють деформацію стиску. Результати автоелектронної скануючої мікроскопії показали, що всі плівки Mo щільні, однорідні і вільні від дефектів і тріщин. При спектроскопічному аналізі спостерігалося збільшення середнього коефіцієнту відбиття плівок Mo з потужністю розпилення спостерігалося у видимому діапазоні спектра. Неконтактна атомно-силова мікроскопія показала, що шорсткість поверхні плівок збільшується зі збільшенням потужності розпилення при постійному струмі. Вимірювання ефекту Холла показало, що електричний опір плівок Mo зменшується, а рухливість носіїв заряду збільшується з ростом потужності розпилення при постійному струмі. Отримані результати свідчать про те, що синтезовані тонкі плівки Мо з потужністю постійного струму 300 Вт мають перспективу застосування як матеріалу зворотного контакту для сполук халькопіритів на основі сонячних елементів завдяки хорошій адгезії та низькому електричному опору

Electrodeposition of template free hierarchical ZnO nanorod arrays via a chloride medium

We have successfully grown template and buffer free ZnO nanorod films via chloride medium by controlling bath temperature in a simple and cost effective electrochemical deposition method. Thin films of ZnO nano-rods were obtained by applying a potential of −0.75 V by employing Ag/AgCl reference electrode for 4 h of deposition time. The CV measurements were carried out to determine potential required to deposit ZnO nanorod films whereas chronoamperometry studies were carried out to investigate current and time required to deposit ZnO nanorod films. The formation of ZnO nanorod has been confirmed by scanning electron microscopy (SEM) and Raman spectroscopy. Low angle XRD analysis confirms that ZnO nanorod films have preferred orientation along (101) direction with hexagonal wurtzite crystal structure. The SEM micrographs show nice surface morphology with uniform, dense and highly crystalline hexagonal ZnO nanorods formation. Bath temperature has a little influence on the orientation of nanorods but has a great impact on their aspect ratio. Increase in bath temperature show improvement in crystallinity, increase in diameter and uniform distribution of nanorods. Compositional analysis shows that the amount of oxygen is ~49.35 % and that of Zn is ~50.65 %. The optical band gap values were found to be 3.19 and 3.26 eV for ZnO nanorods prepared at bath temperature 70 and 80 °C respectively. These results indicate that by controlling the bath temperature band gap of ZnO nanorods can be tailored. The obtained results suggest that it is possible to synthesize ZnO nanorod films by a simple, cost effective electrodeposition process which can be useful for opto-electronic devices fabrication

Synthesis and Characterization of Molybdenum Back Contact Using Direct Current-Magnetron Sputtering for Thin Film Solar Cells

In present work, we report synthesis of molybdenum (Mo) thin films by direct current (DC)-magnetron sputtering method. The structural, optical, morphological, and electrical properties were investigated as a function of target-to-substrate distance. From the results, it is evident that with increase in target-to-substrate distance the thickness of films decreases while its sheet resistance and electrical resistivity increases, which is confirmed by van der Pauw method. Low angle XRD analysis revealed that with increase in target-to-substrate distance preferred orientation of Mo crystallites changes from (211) to (110) and its size decreases. The field emission scanning electron microscope (FE-SEM) analysis revealed a significant change in surface morphology with increase in target-to-substrate distance. UV-Visible spectroscopy analysis showed that Mo films deposited at higher target-to-substrate distance have more reflection than those deposited at lower target-to-substrate. Finally, adhesion test was performed using scotch hatch tape adhesion test which show all Mo films have excellent adhesion over the entire range of target-to-substrate distance studied. The employment of such Mo films as back contact can be useful to improve efficiency of CZTS solar cells

Effect of calcination on structural, morphological and photoelectrochemical performance of SnO2/TiO2 nanostructure films

In the present work, one dimensional rutile-TiO2nanoneedles (NNs) and nanorods (NRs) were grown directly on transparent conductive fluorine-doped SnO2-coated (FTO) glass substrates by chemical bath deposition (CBD) method using titanium (III) chloride as the precursor, followed by calcination at two different temperatures. The heat treatment leads to the conversion of TiO2 nanoneedles into nanorods with reduction in length and enhancement in diameter. The TiO2 nanostructure displayed a diameter range of 11.3–21.7 nm and a length range of 97.7–55.8 nm. The photoelectrochemical evaluation showed that rutile-TiO2 nanostructure exhibited excellent stability upon annealing in a temperature range of 200–400 °C. Optical studies showed that rutile-TiO2 nanostructure has a high absorption coefficient and a direct band gap. The band gap decreased slightly (3.14–3.03 eV) with increasing calcination temperature. The ease of deposition of rutile-TiO2 nanostructure with different morphologies at low temperature provides a new insight for potential applications in solar cells, sensors, catalysis and separation technology

Environmentally stable lead-free cesium bismuth iodide (Cs3Bi2I9) perovskite: Synthesis to solar cell application

In this paper, we synthesized lead-free cesium bismuth iodide (Cs3Bi2I9) perovskite films by solution process using one-step spin-coating technique. Formation of Cs3Bi2I9 perovskite was confirmed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy analysis. The XRD analysis showed that all Cs3Bi2I9 perovskite films were polycrystalline in nature, with hexagonal crystal structure and preferred-orientation along (006) direction. The environmental stability of Cs3Bi2I9 perovskite was confirmed by XRD analysis and UV–visible spectroscopy. Multiple XRD and UV–Vis spectra taken after long time spans revealed the stable nature of Cs3Bi2I9 perovskite films. The UV–visible spectroscopy and photoluminescence analysis showed that the perovskite films absorbed strongly in the visible region and had an optical band gap of ∼2.1 eV. Surface morphology of Cs3Bi2I9 perovskite over the entire substrate surface was investigated using scanning electron microscopy. Thermo-gravimetric analysis showed that Cs3Bi2I9 perovskite was thermally stable up tõ420 °C. Finally, solar cells fabricated using Cs3Bi2I9 perovskite material showed maximum power conversion efficiency (PCE) of 0.17%, with short circuit current density of 1.43 mA/cm2, open circuit voltage of 0.37 V and fill factor of 32%. Applying compositional engineering and optimizing the device structure should further improve the PCE. These results are a significant step toward fabrication of Cs3Bi2I9 perovskite-based solar cells

Effect of calcination on structural, morphological and photoelectrochemical performance of SnO2/TiO2 nanostructure films

In the present work, one dimensional rutile-TiO2nanoneedles (NNs) and nanorods (NRs) were grown directly on transparent conductive fluorine-doped SnO2-coated (FTO) glass substrates by chemical bath deposition (CBD) method using titanium (III) chloride as the precursor, followed by calcination at two different temperatures. The heat treatment leads to the conversion of TiO2 nanoneedles into nanorods with reduction in length and enhancement in diameter. The TiO2 nanostructure displayed a diameter range of 11.3–21.7 nm and a length range of 97.7–55.8 nm. The photoelectrochemical evaluation showed that rutile-TiO2 nanostructure exhibited excellent stability upon annealing in a temperature range of 200–400 °C. Optical studies showed that rutile-TiO2 nanostructure has a high absorption coefficient and a direct band gap. The band gap decreased slightly (3.14–3.03 eV) with increasing calcination temperature. The ease of deposition of rutile-TiO2 nanostructure with different morphologies at low temperature provides a new insight for potential applications in solar cells, sensors, catalysis and separation technology