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

Highly Transparent Wafer-Scale Synthesis of Crystalline WS₂ Nanoparticle Thin Film for Photodetector and Humidity-Sensing Applications

In the present investigation, we report a one-step synthesis method of wafer-scale highly crystalline tungsten disulfide (WS₂) nanoparticle thin film by using a modified hot wire chemical vapor deposition (HW-CVD) technique. The average size of WS₂ nanoparticle is found to be 25–40 nm over an entire 4 in. wafer of quartz substrate. The low-angle XRD data of WS₂ nanoparticle shows the highly crystalline nature of sample along with orientation (002) direction. Furthermore, Raman spectroscopy shows two prominent phonon vibration modes of E¹_2g and A_1g at ∼356 and ∼420 cm^–1, respectively, indicating high purity of material. The TEM analysis shows good crystalline quality of sample. The synthesized WS₂ nanoparticle thin film based device shows good response to humidity and good photosensitivity along with good long-term stability of the device. It was found that the resistance of the films decreases with increasing relative humidity (RH). The maximum humidity sensitivity of 469% along with response time of ∼12 s and recovery time of ∼13 s were observed for the WS₂ thin film humidity sensor device. In the case of photodetection, the response time of ∼51 s and recovery time of ∼88 s were observed with sensitivity ∼137% under white light illumination. Our results open up several avenues to grow other transition metal dichalcogenide nanoparticle thin film for large-area nanoelectronics as well as industrial applications

Electrochemical deposition of p-CdTe nanoparticle thin films for solar cell applications

In present work, p-type CdTe nanostructure thin films successfully synthesized on transparent conductive fluorine-doped SnO2-coated (FTO) substrate from acidic bath using three-electrode electrodeposition technique. Influence of applied potential and electrodeposition time on the structural, morphology and opto-electrical properties of the deposited films has been systematically investigated. Raman spectroscopy, low angle XRD, and HR-TEM analysis suggest that electrodeposited thin films have zinc blende cubic crystal structure. At optimized deposition conditions, we have found that CdTe thin films have direct band gap in the range 1.42–1.53 eV with a blue shift in absorption edge which may caused by quantum confinement effects in the CdTe thin films. The Hot probe experiment and Hall coefficient (RH) values confirmed the p-type semiconducting behavior of CdTe thin films. The ease of deposition of p-type CdTe nanostructure with different morphologies at room temperature provides a new insight for potential applications in hetero-junction solar cells technology

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

Electrochemical deposition of p-CdTe nanoparticle thin films for solar cell applications

In present work, p-type CdTe nanostructure thin films successfully synthesized on transparent conductive fluorine-doped SnO2-coated (FTO) substrate from acidic bath using three-electrode electrodeposition technique. Influence of applied potential and electrodeposition time on the structural, morphology and opto-electrical properties of the deposited films has been systematically investigated. Raman spectroscopy, low angle XRD, and HR-TEM analysis suggest that electrodeposited thin films have zinc blende cubic crystal structure. At optimized deposition conditions, we have found that CdTe thin films have direct band gap in the range 1.42–1.53 eV with a blue shift in absorption edge which may caused by quantum confinement effects in the CdTe thin films. The Hot probe experiment and Hall coefficient (RH) values confirmed the p-type semiconducting behavior of CdTe thin films. The ease of deposition of p-type CdTe nanostructure with different morphologies at room temperature provides a new insight for potential applications in hetero-junction solar cells technology

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