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Cardiovascular diseases pose a serious health risk and have a high mortality rate of 31% worldwide. Digoxin is the most commonly prescribed pharmaceutical preparation to cardiovascular patients particularly in developing countries. The effectiveness of the drug critically depends on its presence in the therapeutic range (0.8-2.0 ng mL

This paper explores the possible role of defect states in charge transport in a type II heterointerface formed by ZnO/SnO2 composite nanostructures (CNs) grown using VLS technique. XRD and high-resolution TEM analysis revealed the granular growth of SnO2 in a matrix of ZnO. Raman spectra obtained from CNs were marked by the presence of oxygen vacancies as Raman modes were broadened and shifted. XPS results confirmed the presence of oxygen vacancies in ZnO and SnO2 and Zn interstitials in ZnO, which showed dependence on growth temperature. Photoluminescence (PL) spectra acquired from CNs were marked by the presence of a very broad PL band in the visible region centered around 2.4 eV, while a very weak near-band-edge emission was observed. The PL band in the visible region showed contributions from Zn interstitials (2.4–2.6 eV) and oxygen vacancies (1.9–2.1 eV) in ZnO, and the PL band of SnO2 consisted of primarily oxygen vacancies (1.9–2.1 eV). The PL bands obtained from CNs showed the absence of Sn interstitials in SnO2. The photoluminescence excitation (PLE) spectrum taken from CNs clearly showed absorption in the band gap due to defects. The role of defect states in the charge transfer process in type II heterostructures was further studied by electrical measurements on SnO2/ZnO bilayer thin films. Temperature-dependent I–V characterization showed significant accumulation of charges at the interface, which was released by thermal excitation. It is, therefore, concluded that defects can play a positive role in photocatalytic devices, where excess charge is needed at the interface for catalytic reaction.

A systematic density functional theory investigation of Cs2PbX6 (X = Cl, Br, I) double perovskites is presented. The lattice constants are computed after structure optimization and using Birch-Murnaghan equations, which agree to the experimental literature. The mechanical stability conditions satisfy Born criteria, and the ductile nature is evidenced by the calculated Poisson's (v) and Pugh's ratios (B0/G) because all three double perovskites exhibit values higher than the respective critical values v = 0.26 and B0/G = 1.75. A detailed study of the optoelectronic properties reveals these double perovskites as promising candidates for future optical devices due to their direct band gaps (within 0.45–2.54 eV) and large absorption coefficients 5.95 × 105 cm−1, which are suitable for solar cell applications. ZT calculations demonstrate minute variations within 200–800 K and computed parameter values are quite favorable for thermoelectric applications of these materials in the future. A p-type semiconducting nature is predicted by the computed thermoelectric properties. Additionally, computed refractive indices show Cs2PbBr6 and Cs2PbI6 exhibiting super-luminescent properties in the UV range. Therefore, the studied double perovskites provide further interest for future energy conversion and photonic based technologies.

It is of immense interest to improve the power conversion efficiency of graphene/silicon Schottky junction solar cells. The ultrathin graphene has essential properties, such as tunable work function to increase Schottky barrier height and built-in potential for efficient charge transport in photovoltaic devices. Here, we use plasma-enhanced CVD to grow graphene directly on planar n-type silicon to fabricate solar cells compatible for industrial-level applications. A key component to our accomplishment is the optimization of directly grown, continuous layers of graphene to achieve superior performance. Thus, by controlling the graphene thickness, the work function is significantly improved, the open circuit voltage is increased, and the energy conversion efficiency is enhanced. While the transfer of CVD grown graphene has limitations due to cracks and impurities during the complex process, our direct growth method demonstrates an efficiency of 5.51 % on bare planar silicon with a large device area. Furthermore, the efficiency is remarkably increased to 9.18 % by adding and doping a polymer layer. Interestingly, with the addition of a doped polymer layer, the cell exhibits excellent stability for at least one month. Our result suggests a promising simple path to fabricate high efficiency solar cells at low temperature and low cost.

In this work we studied front electrodes of nickel/silver (Ni/Ag) deposited on Gr/Si solar cell structure using field induced plating. These electrodes also be used as a front electrode on 2D graphene-based devices at very low cost and temperature (

In graphene/silicon (Gr/Si) solar cell antireflection (ARCs) coatings remarkably enhance the power conversion efficiency. Traditionally titanium dioxide and polymethyl methacrylate used an ARC in Gr/Si solar cells. In such cases controlling film thicknesses and smoothness required a lot of efforts. Here we introduced Vanadium Pentoxide (V2O5) as an ARC in Gr/Si solar cells deposited using thermal evaporator. A well smooth controlled thin-film of V2O5 was achieved. It can easily be thermal evaporated because of its low melting temperature. It was observed after V2O5 coating current density of Gr/Si solar cell remarkably increased from 14 mA/cm2 to 28 mA/cm2 without losing the fill factor. It also helps to improve the Voc from 0.41 to 0.44 V. Different layer thickness shows different colors, results show that a 70 nm layer thickness of V2O5 shows the best ARC for single layer Gr/Si solar cell.

Hydrogen passivation, such as forming gas annealing and alneal (aluminum anneal) process, has been investigated for high efficient crystalline silicon solar cell structures, because the hydrogen atoms can reduce the surface recombination velocity. However, hydrogen could not diffuse deeply to passivate various defects within the silicon bulk. Further investigations into the properties of hydrogen in the silicon lead to the control of hydrogen atoms’ charge states for their high diffusivity and reactivity. Also, research of the hydrogenated amorphous silicon nitride (a-SiNx:H) as a hydrogen source induced an ‘advanced hydrogen passivation’. This paper provides a review of advanced hydrogen passivation applied on p-type, n-type and upgraded metallurgical grade crystalline silicon solar cells, respectively. Especially, the regeneration of boron-oxygen related defects, which cause carrier induced degradation, will be closely discussed since most of industrial solar cells are fabricated by boron-doped p-type silicon wafer. Moreover, laser-induced hydrogen passivation, which can locally recover defective area on the solar cells, will be addressed. In the conclusion, proper conditions of advanced hydrogen passivation for the successful improvement of minority carrier lifetime will be summarized.

Photovoltaic (PV) electric power generation has the potential to account for a major portion of power generation in the global power market. Currently, the PV market is dominated by crystalline silicon (c-Si) solar cells which accounts for more than 80% of the share. Lower cost, optimized process parameters and improved PV cell efficiencies are required to reduce the overall cost per watt peak (W). In this regard, PV cell manufacturers are currently adopting thinner wafers, which tends to increase the surface recombination velocity (SRV). Excellent surface passivation at the front and rear of the PV cell becomes imperative for realizing superior efficienciy on c-Si substrates. In this article, our focus is to discuss the role of the surface passivation process for improving the PV cell efficiency. The fundamentals and strategies to improve the surface passivation for c-Si solar cells are discussed. Surface passivation schemes and materials with the ability to offer field effect passivation with dielectric charges (positive/negative) present in the passivation films were reviewed. Moreover, we discuss the use of a thin-dielectric passivation layer with a properly selected work function and band offsets for tunneling contacts, facilitating a higher efficiency potential. Finaly, the front/rear surface passivation schemes required for thinner wafers to maintain higher bulk lifetime and higher efficiencies for c-Si solar cells are presented.

In recent years, graphene (Gr) based solar cells have attracted extensive interest because of their ability to produce low cost and highly efficient solar cells. Conventional Gr/Si Schottky junction based solar cells are mostly fabricated by transfer of graphene on silicon substrate. In current work the direct growth of graphene by using the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique was demonstrated to make fabrication more practical on a large scale. Firstly Gr/Si Schottky junction based solar cells were fabricated, and by optimizing the growth process, power conversion efficiency (PCE) of about 3.5% was achieved. Additionally, we demonstrated a metal insulator semiconductor (MIS) structure by introducing hafnium oxide (HfO2), and an enriched efficiency of 6.68% was reached. Furthermore, the chemical doping of Gr grown on top of HfO2 passivated Si was done and the efficiency was further enhanced by 8.5%. This study also suggests that the Voc of the Gr/HfO2/Si solar cells strongly depends on the thickness of the HfO2 interfacial layer. These solar cells proved reliable as their efficiency was still consistent even after four months. The current study envisions the use of graphene based solar cells for commercial application.

Graphene/silicon (Gr/Si) Schottky junction solar cells represent an alternative low-cost, easy fabrication structure in photovoltaic devices. After graphene's emergence in 2004, the first Gr/Si solar cell was fabricated in 2010, and was able to achieve upto 15% efficiency in less than a decade. This breakthrough in cell efficiency was realized by the fact that Gr has tremendous electrical and optical properties for photovoltaic applications. In this review, we highlight some of the recent progress in Gr/Si heterojunction solar cells. The growth processes of 2D graphene using the CVD process are discussed in detail. Afterwards, the key parameters that help to enhance the power conversion efficiency (PCE) of solar cells are considered. The interface of Gr/Si and the effects of chemical doping on the cell parameters were studied. Lastly, the challenges and limitations along with the future developments for Gr/Si solar cells are discussed in detail.

Digoxin is a cardiac glycoside which is widely used as medication in treatment of congestive heart failure and arrhythmias. Unfortunately, digoxin has small therapeutic range (2 ng/mL), excess digoxin concentration in blood plasma can cause intoxication. Therefore, simple and sensitive procedure is required for strict monitoring of digoxin in blood level to minimize the risk of toxicity. In this paper, we report detection of digoxin using Au-NPs and GO composites synthesized with wet chemistry. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy were employed for the confirmation of Au-NPs attachment on the surface of GO. The synthesized Au-NPs-GO composites were deposited on the surface of glassy carbon electrode (GCE) for electrochemical characterization. The electrodes were further incubated with mercaptoacetic acid (MAA) and digoxin antibody (Ab) for the formation of Ab-MAA-Au-NPs-GO modified electrode. MAA conjugation resulted in a 35 % increase in Ipc and 63 % decrease in charge transfer resistance (Rct). Antibody immobilization on MAA modified electrode resulted a sudden drop in both the cathodic peak (anodic peak) currents Ipc(Ipa). Increase in Rct (940 Ω) after Ab functionalization was due to its proteinic nature, which confirmed the formation of Ab-MAA-Au-NPs-GO modified GCE sensors. Work was further extended to probe the charge transfer characteristics in different dilution of digoxin. 17 % (10 %) decrease in Ipc(Ipa) as the digoxin drug was increased from 0.1 ng/mL to 1000 ng/mL. Linear sweep voltammetry (LSV) was also performed at the end for analytic performance of Ab modified sensor for various digoxin drug dilutions. Two linear regressions for current response against digoxin drug dilution were recorded, which confirmed sensitivity of the sensor was governed by interaction between Ab and digoxin drug coordinated by potassium ions at the electroactive sites. The sensitivity was 154.81 μAcm−2 ng-1 for 2-0.1 ng range and 10.71 μAcm−2 ng-1 in the range of 1000−2 ng. The limit of detection (LoD) was 0.19 ng/mL, which suggested that proposed Ab-MAA-Au-NPs-GO modified GCE electrochemical sensor can be successfully applied for future digoxin drug detection applications.

Molybdenum disulfide (MoS2) has recently emerged as a promising candidate for fabricating ultrathin-film photovoltaic devices. These devices exhibit excellent photovoltaic performance, superior flexibility, and low production cost. Layered MoS2 deposited on p-Si establishes a built-in electric field at MoS2/Si interface that helps in photogenerated carrier separation for photovoltaic operation. We propose an Al2O3-based passivation at the MoS2 surface to improve the photovoltaic performance of bulklike MoS2/Si solar cells. Interestingly, it was observed that Al2O3 passivation enhances the built-in field by reduction of interface trap density at surface. Our device exhibits an improved power conversion efficiency (PCE) of 5.6%, which to our knowledge is the highest efficiency among all bulklike MoS2-based photovoltaic cells. The demonstrated results hold the promise for integration of bulklike MoS2 films with Si-based electronics to develop highly efficient photovoltaic cells.

Thin-film polycrystalline silicon (pc-Si) on foreign (non-silicon) substrates has been researched by various research groups for the production of photovoltaic cells. High quality pc-Si deposition on foreign substrates with superior optical properties is considered to be the main hurdle in cell fabrication. Metal induced crystallization (MIC) is one of the renowned techniques used to produce this quality of material. In the current study, an aluminum induced crystallization (AIC) method was adopted to produce pc-Si thin-film on aluminum nitride (AlN) substrate by a seed layer approach. Aluminum and a-Si layer were deposited using an e-beam evaporator. Various annealing conditions were used in order to investigate the AIC grown pc-Si seed layers for process optimization. The effect of thermal annealing on grain size, defects preferentially crystallographic orientation of the grains were analyzed. Surface morphology was studied using an optical microscope. Poly-silicon film with a crystallinity fraction between 95-100% and an FWHM between 5-6 cm−1 is achievable at low temperatures and for short time intervals. A grain size of about 10 micron can be obtained at a low deposition rate on an AIN substrate. Similarly, Focused ion beam (FIB) also showed that at 425 °C sample B and at 400 °C sample A were fully crystallized. The crystalline quality of pc-Si was evaluated using μ-Raman spectroscopy as a function of annealed conditions and Grazing incidence X-ray diffraction (GIXRD) was used to determine the phase direction of the pc-Si layer. The current study implicates that a poly-silicon layer with good crystallographic orientation and crystallinity fraction is achievable on AIN substrate at low temperatures and short time frames.

Ni/Cu/Ag plated contacts were examined as an alternate to Ag screen printed contacts for silicon (Si) solar cell metallization. To realize a reliable contact for industrial applications, the contact resistance and its adhesion to Si substrates were evaluated. Si surface roughness by picosecond (ps) laser ablation of silicon-nitride (SiNx) antireflection coating (ARC) was done in order to prepare the patterns. The sintering process after Ni/Cu/Ag full metallization in the form of the post-annealing process was applied to investigate the contact resistivity and adhesion. A very low contact resistivity of approximately 0.5 mΩcm2 has been achieved with measurements made by the transfer length method (TLM). Thin finger lines of about 26 μm wide and a line resistance of 0.51 Ω/cm have been realized by plating technology. Improved contact adhesion by combining the ps-laser-ablation and post-annealing process has been achieved. We have shown the peel-off strengths >1 N/mm with a higher average adhesion of 1.9 N/mm. Our pull-tab adhesion tests demonstrate excellent strength well above the wafer breakage force.

Aluminum-induced crystallization (AIC) is usually used for making silicon seed layer. In this paper, we investigated the AIC process varied with different diffusion barrier materials. The barrier materials were native Al oxide, directly deposited Al 2 O 3 , and SiO 2 in AIC process. The effects of these diffusion barrier materials were analyzed by using electron backscatter diffraction (EBSD), Raman spectroscopy, field emission scanning electron microscope (FE-SEM). The results showed that the case of native Al oxide showed diffusion-limited aggregation which usually resulted in polycrystalline structure. On the other hand, the case of SiO 2 layer showed kinetic-limited aggregation, which generally resulted in the mono-crystalline structure. Therefore, we introduced the novel AIC process with SiO 2 layers.

Crystallization of silicon (Si) from amorphous silicon (a-Si) on foreign substrates has been studied by various research institutes. Crystallization of silicon thin-films on foreign substrates acts as an active layer in silicon thinfilm solar cells. In this research, due to the compatibility of thermal stability and expansion coefficient with Si, we used an aluminum nitride (AIN) substrate as an alternative candidate to glass and other ceramic substrates. P-type amorphous Si 5 μm thin-film was deposited using an ebeam evaporator directly on AIN substrates. The deposited layer was annealed at high temperature (°C) with N2 environment in a conventional tube furnace. Optical characterization was done using an optical microscope to investigate the surface morphology of as-grown and annealed samples. A smoother surface with an average grain size of about 3–4 μm was formed after annealing. Reflectance parameters were measured by UV-vis spectrometry. UV-vis-NIR was studied on as-grown and annealed samples to calculate the quality factor of the Si thin-film which was about 84.4 %. X-ray diffraction (XRD) was used to determine the phase direction of the Si thin-film before and after thermal annealing. It was observed that FWHM varied from 7.73 to 9.30 cm−1, Raman shift was from 520 to 522 cm−1, and the stressed level also changed from 180 to 540 Mpa after annealing at high temperature for a long time. Interestingly, a crystallinity fraction was achieved of about 90 % at 1100 °C.

Aluminum induced crystallization (AIC) of amorphous silicon was studied for thin-film solar cell. The AIC have been usually researched on glass substrate which has smooth surface. However, in this paper, the graphite plate was used as a substrate for using thin-film solar cell which has 1μm roughness. The growth silicon layer characteristic could be relatively different with that using glass substrate by the surface roughness. Therefore, the properties of crystallized silicon layer were studied for grain size analysis with variation in temperature and time during the AIC annealing process. The crystalline fraction and crystallinity was analyzed by Optical microscope, X-ray diffraction (XRD), and Raman spectrometer measurement methods. Additionally, the grain size was also relatively analyzed with FWHM results. As a result of measurements, crystalline fraction of grown silicon was increased with the increasing of temperature and time. The maximum crystalline fraction of grown silicon was 92.85% for 2400 minutes of annealing duration at 500°C.

In this paper, we present the effect of various self doping of catalysts (Au, Mn, and Ga) on the emission properties of cubic ZnS nanostructures. The solubility of the catalysts during the growth was confirmed by FESEM, HRTEM, and XRD. XPS confirmed the formation and variation of intrinsic defects like S, Zn vacancies and extrinsic defects created by self-doped catalysts, which varied with the type of catalysts. The luminescence properties of ZnS nanostructures showed strong dependence on the type of catalyst related defects. Low temperature PL spectroscopy showed that the Au created shallow surface defects states (~100 meV from the conduction band, and Ga induced shallow level defect states with emission in the UV ~360 meV). The temperature dependent PL spectroscopy showed strong negative thermal quenching of PL intensity of blue and orange emission in Au catalyzed ZnS nanostructures while Mn and Ga showed quenching behavior only in yellow and blue bands emission, respectively. Time-resolved PL spectra obtained from all nanostructures demonstrated two time decay constants. The percentage contributions of the fast decay (direct recombination of electrons and holes) and slow decay (trapped electrons at the luminescent sites) were determined for three catalyzed ZnS nanostructures. The percentage contributions and long life time components of blue and green bands were high in Au catalyzed ZnS nanostructures, compared to Mn and Ga catalyzed ZnS nanostructures. Present results indicate the potential use in a broad spectrum tunable nanolasers and multi-color light source.

Nanohybrids formed by the multiwalled carbon nanotubes (MWCNTs) and metallic nanoparticles (NPs) have gained immense interest recently for their potential biological applications. In this paper, we present a comprehensive study of the nanohybrid formed with varied concentrations of Au-NPs with MWCNTs. It is demonstrated that the concentration of Au-NPs in the nanohybrid is crucial in defining ultimate characteristics of the nanohybrid. The MWCNTs were functionalized with varied concentrations of Au-NPs (40–100 nano Molar (nM)) and characterized extensively by the X-ray diffraction, electron microscopy, Raman spectroscopy and UV–Vis absorption spectroscopy. The process of purification and acid treatment led to the activation of –COOH bond at the surface of MWCNTs and functionalization with Au-NPs also induced stresses as observed in the X-ray diffraction patterns. The fusion of Au-NPs in the MWCNTs was clearly observed in the high resolution TEM images, which affected the D and G – Raman bands of the MWCNTs significantly as studied by the line shape analysis. The Au-NPs–MWCNTs nanohybrids were then used to study the effect of various concentrations of E-coli using Raman spectroscopy and absorption spectroscopy. Due to intrinsic negative charge present on the E-coli, the local charge densities varied at the surface of MWCNTs as soon as it was covered with E-coli, and resulted in the shift of both G and D bands and increased intensity ratio of the two bands. The variation in the charge density in Au-NPs due to its binding with MWCNTs and adsorption of E-coli was reflected in the blue shift of the surface plasmon modes. Finally, it is concluded that ratio of Au-NPs and MWCNTs is crucial in forming nanohybrid for applications.

Fabrication of crystalline silicon thin-film solar cells (CSiTFSC’s) on foreign substrates (non-silicon materials) has been studied at various photovoltaic research institutes. The primary motivation behind the use of foreign substrates is to significantly reduce the consumption of solar-grade silicon, and that use may also completely eradicate the need for wafer production by sawing. The impact of foreign substrates as a substitute is significant in terms of savings in comparison to conventional production of silicon-based solar cells in the photovoltaic industry. High temperature crystalline silicon film deposition is favorable for increasing the efficiency of CSiTFSC’s on carbon based ceramics substrates. High-temperature processes provide an opportunity to deposit silicon films with larger grain sizes at higher deposition rates. Graphite and silicon-carbide substrates containing elemental carbon have been studied. Thus far, efficiencies in the range of 13.4% for graphite and 15% for silicon-carbide substrates have been demonstrated. A detailed overview of the processes adopted for solar-cell implementation on carbon substrates is addressed in the literature.

Molybdenum disulfide (MoS

Aluminum-induced crystallization (AIC) is one process which increases silicon grain size at low temperatures. In this study, we analyzed the effect of silicon crystallization according to the aluminum deposition conditions in the AIC process using silicon oxide. The initial aluminum layer was analyzed using a field emission-scanning electron microscopy (FE-SEM) after cutting the samples with a focused-ion-beam (FIB). Through FE-SEM, we observed that the aluminum grain size of the original aluminum layer increased in proportion to the aluminum deposition temperature. However, not only aluminum grain size but also surface roughness and porosity of the initial aluminum layer were increased. The initial aluminum layer, according to the deposition temperature, significantly affected the crystallized silicon grain size. The silicon grain size was decreased from 16.97 μm to 7.81 μm according to the increase of the aluminum deposition temperature. This was because the Si diffusion area was increased by the increase of the aluminum surface roughness.

The thickness effects of SiOx which was deposited as an intermediate layer between aluminum and silicon were studied on Aluminum-induced crystallization (AIC). The SiOx layer thickness varied from 2 nm to 20 nm and affected the crystallization process of the AIC. In the case of the thin SiOx layer, crystallized silicon morphology showed kinetic-limited aggregation. On the other hand, crystallized silicon processed with the thick SiOx layer showed diffusion-limited aggregation due to slow silicon diffusion velocity. Kinetic-limited aggregation showed large grain. The schematic crystallization model was used to describe the relationship between crystallization and grain size in this paper.

In this paper, we report the effect of 1.5 MeV proton beam irradiation dose on the structural and electrical properties of TiO2 thin films deposited on n-Si substrates. The formation and transformation of different TiO2 phases in the irradiated thin films were characterized by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). X-ray diffraction measurements revealed that the as grown film was rich in Ti5O9 phase and then converted to mixed phases of TiO2 (rutile and anatase) after exposure with radiation doses up to 5 x 10(14) cm(-2). The XPS results revealed the formation of oxygen vacancy (negative) traps in the exposed TiO2 films, which showed strong dependence on the dose. The C-V measurements showed that proton radiations also damaged the Si substrate and created deep level defects in the substrate, which caused a shift of 0.26 +/- 0.01V in the flat band voltage (V-FB). I-V measurements showed that the ideality factor increased and the rectification ratio dropped with the increase in the radiation dose. The present study showed the stability of TiO2/Si interface and TiO2 film as an oxide layer against proton radiations. (C) 2014 AIP Publishing LLC.