Hydrogenated Nanocrystalline Silicon Thin Films Prepared by Hot-Wire Method with Varied Process Pressure

Hydrogenated nanocrystalline silicon films were prepared by hot-wire method at low substrate temperature (200∘C) without hydrogen dilution of silane (SiH4). A variety of techniques, including Raman spectroscopy, low angle X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and UV-visible (UV-Vis) spectroscopy, were used to characterize these films for structural and optical properties. Films are grown at reasonably high deposition rates (>15 Å/s), which are very much appreciated for the fabrication of cost effective devices. Different crystalline fractions (from 2.5% to 63%) and crystallite size (3.6–6.0 nm) can be achieved by controlling the process pressure. It is observed that with increase in process pressure, the hydrogen bonding in the films shifts from Si–H to Si–H2 and (Si–H2)n complexes. The band gaps of the films are found in the range 1.83–2.11 eV, whereas the hydrogen content remains <9 at.% over the entire range of process pressure studied. The ease of depositing films with tunable band gap is useful for fabrication of tandem solar cells. A correlation between structural and optical properties has been found and discussed in detail

Ternary Cu2SnS3: synthesis, structure, photoelectrochemical activity, and heterojunction band offset and alignment

Ternary Cu2SnS3 (CTS) is an attractive nontoxic and earth-abundant absorber material with suitable optoelectronic properties for cost-effective photoelectrochemical applications. Herein, we report the synthesis of high-quality CTS nanoparticles (NPs) using a low-cost facile hot injection route, which is a very simple and nontoxic synthesis method. The structural, morphological, optoelectronic, and photoelectrochemical (PEC) properties and heterojunction band alignment of the as-synthesized CTS NPs have been systematically characterized using various state-of-the-art experimental techniques and atomistic first-principles density functional theory (DFT) calculations. The phase-pure CTS NPs confirmed by X-ray diffraction (XRD) and Raman spectroscopy analyses have an optical band gap of 1.1 eV and exhibit a random distribution of uniform spherical particles with size of approximately 15–25 nm as determined from high-resolution transmission electron microscopy (HR-TEM) images. The CTS photocathode exhibits excellent photoelectrochemical properties with PCE of 0.55% (fill factor (FF) = 0.26 and open circuit voltage (Voc) = 0.54 V) and photocurrent density of −3.95 mA/cm2 under AM 1.5 illumination (100 mW/cm2). Additionally, the PEC activities of CdS and ZnS NPs are investigated as possible photoanodes to create a heterojunction with CTS to enhance the PEC activity. CdS is demonstrated to exhibit a higher current density than ZnS, indicating that it is a better photoanode material to form a heterojunction with CTS. Consistently, we predict a staggered type-II band alignment at the CTS/CdS interface with a small conduction band offset (CBO) of 0.08 eV compared to a straddling type-I band alignment at the CTS/ZnS interface with a CBO of 0.29 eV. The observed small CBO at the type-II band aligned CTS/CdS interface points to efficient charge carrier separation and transport across the interface, which are necessary to achieve enhanced PEC activity. The facile CTS synthesis, PEC measurements, and heterojunction band alignment results provide a promising approach for fabricating next-generation Cu-based light-absorbing materials for efficient photoelectrochemical applications

Solution-processed Cd-substituted CZTS nanocrystals for sensitized liquid junction solar cells

The Earth-abundant kesterite Cu2ZnSnS4 (CZTS) exhibits outstanding structural, optical, and electronic properties for a wide range of optoelectronic applications. However, the efficiency of CZTS thin-film solar cells is limited due to range of factors, including electronic disorder, secondary phases, and the presence of anti-site defects, which is key factor limiting the Voc. The complete substitution of Zn lattice sites in CZTS nanocrystals (NCs) with Cd atoms offers a promising approach to overcome several of these intrinsic limitations. Herein, we investigate the effects of substitution of Cd2+ into Zn2+ lattice sites in CZTS NCs through a facile solution-based method. The structural, morphological, optoelectronic, and power conversion efficiencies (PCEs) of the NCs synthesized have been systematically characterized using various experimental techniques, and the results are corroborated by first-principles density functional theory (DFT) calculations. The successful substitution of Zn by Cd is demonstrated to induce a structural transformation from the kesterite phase to the stannite phase, which results in the bandgap reducing from 1.51 eV (kesterite) to 1.1 eV (stannite), which is closer to the optimum bandgap value for outdoor photovoltaic applications. Furthermore, the PCE of the novel Cd-substituted liquid junction solar cell underwent a four-fold increase, reaching 1.1%. These results highlight the importance of substitutional doping strategies in optimizing existing CZTS-based materials to achieve improved device characteristics

Synthesis of gamma-WO3 thin films by hot wire-CVD and investigation of its humidity sensing properties

In this study, monoclinic tungsten oxide (gamma-WO3) have been grown in a single step using HW-CVD method by resistively heating W filaments in a constant O-2 pressure. The formation of gamma-WO3 was confirmed using low angle-XRD and Raman spectroscopy analysis. Low angle-XRD analysis revealed that as-deposited WO3 film are highly crystalline and the crystallites have preferred orientation along the (002) direction. HRTEM analysis and SAED pattern also show the highly crystalline nature of WO3 with d spacing of similar to 0.38 nm, having an orientation along the (002) direction. Surface topography investigated by SEM analysis shows the formation of a uniform and homogeneous cauliflower like morphology throughout the substrate surface without flaws and cracks. A humidity sensing device incorporating WO3 is also fabricated, which shows a maximum humidity sensitivity factor of similar to 3954% along with a response time of similar to 14 s and a recovery time of similar to 25 s. The obtained results demonstrate that it is possible to synthesize WO3 in a single step by HW-CVD method and to fabricate a humidity sensor by using it

Experimental investigation of the thermal power pump cycle - Proof of concept

This paper presents an experimental investigation of a water pump based on the thermal power pump (TPP) cycle. The pump is intended to effectively utilise low grade heat sources (below 100 °C) in order to pump water at high pressures. A piston-cylinder device has been created that operates on the TPP cycle and it is shown that significant delivery pressures are obtainable, up to 20 m head for a heat source of approximately 80 °C. The overall efficiencies obtained by the TPP system investigated here ranged from 0.36 to 0.48% for delivery heads from 5 to 20 m. The experimental results show that due to thermal cycling of the system, around 55-60% of heat input is not available for work conversion

Synthesis of orthorhombic-molybdenum trioxide (α-MoO3) thin films by hot wire-CVD and investigations of its humidity sensing properties

In present work, we report synthesis of orthorhombic-molybdenum trioxide (α-MoO 3 ) thin films using home-build hot wire-CVD (HW-CVD) method simply by heating the Mo filament in a controlled O 2 atmosphere. The formation of α-MoO 3 was confirmed by low angle-XRD and Raman spectroscopy. Low angle-XRD analysis revealed that α-MoO 3 crystallites have orientations along (110), (101) and (111) directions while Raman spectroscopy analysis shows two prominent vibrational modes ~819 and ~994 cm -1 associated with Mo 2 -O and Mo=O respectively. SEM and TEM analysis show the formation of nano-sheets like morphology of α-MoO 3 thin films. The SAED pattern shows highly crystalline nature of α-MoO 3 . The humidity-sensing properties were investigated at room temperature by fabricating the two probe device. The humidity sensing results showed n-type behavior of α-MoO 3 . The maximum humidity sensitivity of ~6957% along with response time of ~66 s and recovery time of ~5 s were observed for α-MoO 3 thin film humidity sensor device. Our results have opened up a new avenue to grow α-MoO 3 for humidity sensor applications

Kinetics of ethynylation of formaldehyde to butynediol

Activity of Cu catalysts and kinetics of ethynylation of formaldehyde using Cu2C2 catalyst has been studied. The reaction was found to be 0.41 and 0.58 order with respect to acetylene and formaldehyde concentrations, respectively. The activation energy of the reaction was found to be 15.13 kcal/mol

Investigation on sub nano-crystalline silicon thin films grown using pulsed PECVD process

Present work discusses the structural modifications in intrinsic layer of hydrogenated amorphous silicon (a-Si: H) deposited using Pulsed Wave Plasma Enhanced Chemical Vapor Deposition (PW-PECVD) technique which highlights the crystallite formation within the boundaries of nano crystallite silicon thin films. These investigations were carried out for the films deposited under the variation of applied pulsed power from 10W to 60 W. The resultant film phases were generalized as sub-nano crystalline silicon phases. The evolution of such phases has been effectively probed using various spectroscopic and structural characterization techniques including Raman spectroscopy, Fourier Transform Infrared spectroscopy (FTIR), and Field Emission Scanning Electron Microscopy (FESEM). The observed sub-nano crystalline volume fraction varies from similar to 28-46%. This marks the modification in crystallite growth from the partial nucleation to coalescence phase. From this the importance of pulsed wave PECVD (PW-PECVD) has been discussed in terms of high growth rates as well as the extended transition zones with the formation of sub-nano crystallite structures. The study found to be specific for understanding the sub-nano crystalline phases in the film silicon having high photo-stability and photo-response like in mu c/nc-Si: H (micro/nano crystalline silicon) and a-Si: H respectively

Adsorption of formaldehyde and butynediol from aqueous solutions on a Cu<SUB>2</SUB>C<SUB>2</SUB>-silica gel catalyst

The effect of equilibrium concentration on adsorption has been studied at different temperatures and the nature of isotherms is discussed. For the formaldehyde-Cu<SUB>2</SUB>C<SUB>2</SUB>-silica gel system, Freundlich type equations describe the data satisfactorily

Dependence of effective doping on structural order in hydrogenated amorphous silicon

Electrical and structural measurements have been made on intrinsic and phosphorus doped a-Si&#166;H films deposited by R.F. glow discharge at different substrate temperatures (T<SUB>s</SUB>) in the range (50-400&#176;C). Effective doping, parameterised as ratio of dark conductivity of the doped film to that of the intrinsic film deposited at the same temperature is maximum around 250&#176;C. Gap state density inferred from DLTS results shows an increase beyond 250&#176;C. The average bond angle deviation &#916;&#952; in the amorphous network, is also minimum around 250&#176;C and increases for higher T<SUB>s</SUB>. The results bring out a good correlation between effective doping and the bond angle deviation, an important element of the short range order in the amorphous network