Structural and optical properties of CdTe thin films deposited using RF Magnetron sputtering

In this work, we have studied the influence of RF power on structural and optical properties of CdTe thin films deposited by indigenously designed locally fabricated RF magnetron sputtering. Films were analyzed by using variety of techniques such as low angle X- ray diffraction, UV-Visible spectroscopy, Raman spectroscopy etc. to study its structural and optical properties. Low angle XRD analysis showed that CdTe films are polycrystalline and has cubic structure with preferred orientation in (111) direction. Raman scattering studies revealed the presence of CdTephase over the entire range of RF power studied. The UV-Visible spectroscopy analysis showed that the band gap decreases with increase in RF power. However, CdTe films deposited at higher RF power has optimum band gap values (1.44-1.60 eV). Such optimum band gap CdTe can be use as absorber material in CdS/CdTe and ZnO/CdTe solar cells

Growth of hydrogenated nano-crystalline silicon (nc-Si:H) films by plasma enhanced chemical vapor deposition (PE-CVD)

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were prepared by home-made PE-CVD systemfromgas mixture of pure SiH4 and H2 at various deposition pressures. Obtained results exhibited that deposition rate increases with increase in deposition pressure. Raman spectroscopy analysis revealed that deposition pressure in PE-CVD is a critical process parameter to induce nanocrystallization in Si:H films. The FTIR spectroscopy analysis results indicate that with increase in deposition pressure hydrogen bonding in films shifts from Si-H to Si-H2 and (Si-H2)n bonded species bonded species. The bonded hydrogen content didn’t show particular trend with optical band gap with change in deposition pressure. The obtained results indicates that 400 mTorr is an optimized deposition pressure of our PE-CVD unit to synthesize nc-Si:H films. At this optimized deposition pressure nc-Si:H films with crystallite size ∼ 5.43 nm having good degree of crystallinity (∼77%) and high band gap (ETauc∼ 1.85 eV) were obtained with a low hydrogen content (4.28 at. %) at moderately high deposition rate (0.75 nm/s). The ease of the present work is to optimize deposition pressure to obtain device quality intrinsicnc-Si:H layer in view of its used in p-i-n solar cells

Single Crystal, High Band Gap CdS Thin Films Grown by RF Magnetron Sputtering in Argon Atmosphere for Solar Cell Applications

Single crystal thin films of CdS were grown onto glass substrates by RF magnetron sputtering at var ious substrate temperatures. Structural, optical and morphology properties of these films were investigated through low angle XRD, Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive x-ray (EDX) spectroscopy, UV-Visible spectroscopy etc. Formation of single crystal CdS films has been confirmed by low angle XRD and Raman spectroscopy analysis. Low angle XRD showed that CdS films has preferred orientation in (111) direction. Improvement of crystallinity and increase in average grain size of CdS crystallites has been observed with increase in substrate temperature. Surface morphology investigated using SEM showed that CdS films deposited over entire range of substrate temperature are highly smooth, dense, homogeneous, and free of flaws and cracks. The EDX data revealed the formation of high-quality nearly stoichiometric CdS films by RF magnetron sputtering. Furthermore, the CdS films deposited at low substrate temperatures (< 200 0C) are slightly S rich while deposited at higher substrate temperatures (> 200 0C) are slightly Cd rich. The UV-Visible spectroscopy analysis showed that an average transmission ~ 80-90 % in the visible range of the spectrum having band gap ~ 2.28 -2.38 eV, which is quite close to the optimum value of band gap for a buffer layer in CdTe/CdS, Cu2S/CdS hetero-junction solar cells

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

Structural, electronic, and optical properties of lead-free halide double perovskite Rb2AgBiI6: a combined experimental and DFT study

Hybrid lead halide perovskites have emerged as an attractive photoactive semiconductor for optoelectronic applications such as photovoltaics. However, their toxicity and stability issues pose significant challenges to its wide-scale applications and hence the need to find alternative perovskites that are stable and environmentally benign. Recently, double perovskites have been suggested as a potential alternative owing to their non-toxicity and high stability. In the present study, we report the first synthesis of Rb2AgBiI6 thin films in a cubic crystal structure using a facile room-temperature single-step solution process synthesis method and explore their potential optoelectronic applications. The structural, thermal, and mechanical stability, electronic, and optical properties are studied using various experimental techniques, and the results are further corroborated by first-principles density functional theory (DFT) calculations. The Rb2AgBiI6 film has an estimated band gap ∼ of 1.98 eV with the demonstrated thermal stability of ∼ 440 oC, suggesting its potential suitability for low-cost thin-film solar cells. The initial fabricated photovoltaic device without optimization of the synthesis conditions and device architecture show power conversion efficiency (PCE) of 0.1 % and an open-circuit voltage (Voc) of 0.46 V. The successful incorporation of Rb in Bi-based double perovskite should open the way to a new class of Rubidium-based perovskites with significant potential for optoelectronic applications

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

Structural and optical properties of CdTe thin films deposited using RF Magnetron sputtering

In this work, we have studied the influence of RF power on structural and optical properties of CdTe thin films deposited by indigenously designed locally fabricated RF magnetron sputtering. Films were analyzed by using variety of techniques such as low angle X- ray diffraction, UV-Visible spectroscopy, Raman spectroscopy etc. to study its structural and optical properties. Low angle XRD analysis showed that CdTe films are polycrystalline and has cubic structure with preferred orientation in (111) direction. Raman scattering studies revealed the presence of CdTephase over the entire range of RF power studied. The UV-Visible spectroscopy analysis showed that the band gap decreases with increase in RF power. However, CdTe films deposited at higher RF power has optimum band gap values (1.44-1.60 eV). Such optimum band gap CdTe can be use as absorber material in CdS/CdTe and ZnO/CdTe solar cells

Soft annealing effect on the properties of sputter grown Cu2ZnSnS4 (CZTS) thin films for solar cell applications

In present study, CZTS films were fabricated using 2 different processes and their properties have been compared. The first is a 2-stage process which includes deposition of CZT followed by sulfurization and the second is a 3-stage process which includes deposition of identical CZT, soft annealing (pre-heating) and sulfurization. Structural, morphological, optical and compositional properties of CZTS films are investigated by XRD, Raman spectroscopy, FE-SEM, UV–Visible spectroscopy, EDS and photoresponse measurements. Structural analysis revealed that films prepared by both processes have polycrystalline kesterite-CZTS structure and exhibit prefered orientation along (1 1 2) direction. It has been observed that soft annealing temperature in 3-stage process significantly improve the crystal quality of CZTS films. Surface morphology of films sulfurized at 550 °C shows a uniform and compact micrograin (∼0.31 µm) without cracks. The soft annealing temperature significantly improves micrograin size (∼0.49 µm) and compactness of CZTS films. UV–Visible spectroscopy showed that the band gap of all CZTS films is in optimal range. The CZTS films fabricated by 3-stage process, exhibits high photocurrent response under intermittent visible-light irradiation, implying that they can useful as an absorber layer in solar cells

Growth of hydrogenated nano-crystalline silicon (nc-Si:H) films by plasma enhanced chemical vapor deposition (PE-CVD)

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were prepared by home-made PE-CVD systemfromgas mixture of pure SiH4 and H2 at various deposition pressures. Obtained results exhibited that deposition rate increases with increase in deposition pressure. Raman spectroscopy analysis revealed that deposition pressure in PE-CVD is a critical process parameter to induce nanocrystallization in Si:H films. The FTIR spectroscopy analysis results indicate that with increase in deposition pressure hydrogen bonding in films shifts from Si-H to Si-H2 and (Si-H2)n bonded species bonded species. The bonded hydrogen content didn’t show particular trend with optical band gap with change in deposition pressure. The obtained results indicates that 400 mTorr is an optimized deposition pressure of our PE-CVD unit to synthesize nc-Si:H films. At this optimized deposition pressure nc-Si:H films with crystallite size ∼ 5.43 nm having good degree of crystallinity (∼77%) and high band gap (ETauc∼ 1.85 eV) were obtained with a low hydrogen content (4.28 at. %) at moderately high deposition rate (0.75 nm/s). The ease of the present work is to optimize deposition pressure to obtain device quality intrinsicnc-Si:H layer in view of its used in p-i-n solar cells

Soft annealing effect on the properties of sputter grown Cu2ZnSnS4 (CZTS) thin films for solar cell applications

In present study, CZTS films were fabricated using 2 different processes and their properties have been compared. The first is a 2-stage process which includes deposition of CZT followed by sulfurization and the second is a 3-stage process which includes deposition of identical CZT, soft annealing (pre-heating) and sulfurization. Structural, morphological, optical and compositional properties of CZTS films are investigated by XRD, Raman spectroscopy, FE-SEM, UV–Visible spectroscopy, EDS and photoresponse measurements. Structural analysis revealed that films prepared by both processes have polycrystalline kesterite-CZTS structure and exhibit prefered orientation along (1 1 2) direction. It has been observed that soft annealing temperature in 3-stage process significantly improve the crystal quality of CZTS films. Surface morphology of films sulfurized at 550 °C shows a uniform and compact micrograin (∼0.31 µm) without cracks. The soft annealing temperature significantly improves micrograin size (∼0.49 µm) and compactness of CZTS films. UV–Visible spectroscopy showed that the band gap of all CZTS films is in optimal range. The CZTS films fabricated by 3-stage process, exhibits high photocurrent response under intermittent visible-light irradiation, implying that they can useful as an absorber layer in solar cells