Adinath Funde

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 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.

Carbon nanotube–amorphous silicon hybrid solar cell with improved conversion efficiency

We report a hybrid solar cell based on single walled carbon nanotubes (SWNTs) interfaced with amorphous silicon (a-Si). The high quality carbon nanotube network was dry transferred onto intrinsic a-Si forming Schottky junction for metallic SWNT bundles and heterojunctions for semiconducting SWNT bundles. The nanotube chemical doping and a-Si surface treatment minimized the hysteresis effect in current-voltage characteristics allowing an increase in the conversion efficiency to 1.5% under an air mass 1.5 solar spectrum simulator. We demonstrated that the thin SWNT film is able to replace a simultaneously p-doped a-Si layer and transparent conductive electrode in conventional amorphous silicon thin film photovoltaics.

Low substrate temperature deposition of transparent and conducting ZnO:Al thin films by RF magnetron sputtering

Transparent and conducting Al-doped ZnO (ZnO:Al) films were prepared on glass substrate using the RF sputtering method at different substrate temperatures from room temperature (RT) to 200℃. The structural, morphological, electrical and optical properties of these films were investigated using a variety of characterization techniques such as low angle XRD, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), Hall measurement and UV-visible spectroscopy. The electrical properties showed that films deposited at RT have the lowest resistivity and it increases with an increase in the substrate temperature whereas carrier mobility and concentration decrease with an increase in substrate temperature. Low angle XRD and Raman spectroscopy analysis reavealed that films are highly crystalline with a hexagonal wurtzite structure and a preferred orientation along the c-axis. The FE-SEM analysis showed that the surface morphology of films is strongly dependent on the substrate temperature. The band gap decreases from 3.36 to 3.29 eV as the substrate temperature is increased from RT to 200℃. The fundamental absorption edge in the UV region shifts towards a longer wavelength with an increase in substrate temperature and be attributed to the Burstein-Moss shift. The synthesized films showed an average transmission (>85%) in the visible region, which signifies that synthesized ZnO:Al films can be suitable for display devices and solar cells as transparent electrodes.

Substrate temperature dependent studies on properties of chemical spray pyrolysis deposited CdS thin films for solar cell applications

Thin films of CdS have been prepared by chemical spray pyrolysis by spraying precursor solution directly onto soda lime glass (SLG) substrates. Influence of substrate temperature on structural, optical, morphological and electrical properties have been investigated by using various techniques such as low angle X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), UV–visible spectroscopy photoluminescence (PL) spectroscopy etc. Formation of CdS has been confirmed by low angle XRD, Raman spectroscopy and XPS analysis. XRD pattern showed that CdS films are polycrystalline, have hexagonal structure and prefer orientation of crystallites shifts from (101) to (002) with increase in substrate temperature. Raman spectroscopy revealed that exciton-phonon coupling depends on substrate temperature and hence on crystallite size. Optical band gap increased from 2.43 to 2.99 eV when substrate temperature increased from 325 to . Transmittance of the film also showed an increasing trend from to with increase in substrate temperature. Such high band gap and transmittance values of CdS films prepared at make it a useful window material in CdS/CdTe and CdS/Cu2S heterojunction solar cells.

Synthesis of Cubic Nanocrystalline Silicon Carbide (3C-SiC) Films by HW-CVD Method

Cubic nanocrystalline silicon carbide (3C-SiC) films have been deposited by using the hot wire chemical vapor deposition (HW-CVD) method at a low substrate temperature and at high deposition rate. Structural, optical and electrical properties of these films have been investigated as a function of H2 dilution ratio. The formation of 3C-SiC films has been confirmed from low angle XRD analysis, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS) and dark and photoconductivity measurements. The FTIR spectroscopy analysis revealed that the bond densities of Si-H and C-H decrease while that of Si-C increases with increase in the H2 dilution ratio. The total hydrogen content decreases with increase in H2 dilution ratio and was found < 15 at. % over the entire range of H2 dilution ratio studied whereas the band gap show an increasing trend with increase in the H2 dilution ratio.

Structural and optical investigations of nc‐Si:H thin films prepared by hot‐wire method

Structural and optical properties of hydrogenated nanocrystalline silicon (nc‐Si:H) films have been carefully studied as a function of hydrogen dilution of silane (RH.) Raman spectroscopic analysis showed that with increase in RH, the crystalline fraction in the films increases whereas crystallite size remains almost constant (∼8.7 nm). Also, the Raman spectra shows a blue shift of transverse optic (TO) phonon mode indicating that the films are stressed and the induced stress is compressive. The FTIR spectroscopic analysis revealed that the hydrogen predominantly incorporated in Si‐H2 and (Si‐H2)n bonding configuration. We have obtained high band gap (1.88‐2.07 eV) at low hydrogen content (< 2.5 at. %) over the entire range of RH studied at reasonably high deposition rate (7.4‐9.5 A/s).

Boron Doped p‐type Hydrogenated Nanocrystalline Silicon Films Grown by Hot Wire Chemical Vapor Deposition

In this paper we report on the effect of diborane (B2H6) flow rate on the microstructural and opto‐electrical properties of p‐type nc‐Si:H films grown by HW‐CVD method. An attempt has been made to elucidate the boron doping mechanism of the p‐type nc‐Si:H films. The correlation between B2H6 gas flow rate (FB2H6) and material properties including crystalline volume fraction (XRaman), crystallite size (dRaman), band gap (Eg) and hydrogen content (CH) has been established. We obtained p‐type nc‐Si:H films with high dark conductivity (≤0.2 S/cm), high Eg (>2 eV) at low CH (<3.6 at. %). The employment of these films in nc‐Si:H based p‐i‐n solar cell as a p‐type window layer could have better collection of charge carriers when illuminated from p‐side.

Reliability and efficacy of organic passivation for polycrystalline silicon solar cells at room temperature

Oleylamine is used as a passivating layer instead of commercial high temperature SiNx. Oleylamine coating applied on the n-type emitter side with p-type base polycrystalline silicon solar cells at room temperature using a simple spin coating method. It has been observed that there is 16% increase in efficiency after Oleylamine coating. Further, the solar cell was subjected to standard characterization namely current-voltage measurement for electrical parameters and Fourier transform infrared spectroscopy to understand the interaction of emitter surface and passivating Oleylamine. However, the passivation layer is not stable due to the reaction between Oleylamine and ambient air content such as humidity and carbon dioxide. This degradation can be prevented with suitable overcoating.

Effect of Annealing on Optical and Structural Properties of Rutile TiO2 Nanoarrays

One dimensional rutile-TiO2 nanoneedles (NNs) and nanorods (NRs) were grown directly on transparent conductive Fluorine-doped SnO2-coated (FTO) glass substrates using Chemical Bath Deposition (CBD) method. Titanium (III) chloride was used as the precursor, followed by annealing at 200°C. The heat treatment leads to the conversion of TiO2 nanoneedles into nanorods. Optical studies revealed that rutile-TiO2 thin films have a high absorption coefficient and a direct bandgap which decreased slightly (3.14-3.09 eV) by applying heat treatment .The ease of deposition of rutile-TiO2 nanocomposite with different morphologies at low temperature provides a new insight for potential applications in solar cells, sensors, catalysis and separation technology.

BORON DOPED nc-Si:H WINDOW LAYER PREPARED BY HW-CVD FOR SOLAR CELL APPLICATIONS

In this work, we report on synthesis of boron doped hydrogenated nanocrystalline silicon (p-nc-Si:H) films by HW-CVD method. Films were prepared at low substrate temperature (165 °C) and low process pressure (20 mTorr) by varying diborane gas phase ratio [defined as RB2H6 = (FB2H6/FSiH4)×100%]. The material properties of these films are studied using micro-Raman spectroscopy, low angle X-ray diffraction, X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy, dark conductivity measurements etc. The correlation between RB2H6 and resulting material properties such as crystalline volume fraction, crystallite size, band gap and hydrogen content has been established. We have obtained high band gap (~ 2.48 eV) p-nc-Si:H films having dark conductivity (~ 0.6 S/cm) with low hydrogen content (~ 1.8 at. %) at high deposition rate (~19.2 A/s). The employment of these films in a-Si:H based p-i-n solar cell as a p-type window layer could have low absorption losses thereby enhancing the current density which i...