Kalaga Murali Krishna

Optical Absorption and Electrical Conductivity of Amorphous Carbon Thin Films from Camphor: A Natural Source.

Thin films of carbon have been deposited on n-type single-crystal silicon and quartz substrates by simple ion beam sputtering of camphoric carbon, obtained from camphor, a natural source. Optical absorption coefficients of 104–105 cm-1 have been obtained for the as-deposited and annealed films and the absorption coefficient increased upon annealing. The optical band-gap energy of the as-deposited camphoric carbon thin film derived from optical absorption measurements is 0.5 eV. Effects of annealing on various optical and electrical properties are studied, in light of the semiconducting nature of these films, through the electrical conduction mechanism. The results obtained are discussed and compared with the literature.

Photovoltaic and spectral photoresponse characteristics of n-C/p-C solar cell on a p-silicon substrate

Recent studies have shown the application of amorphous carbon as a semiconductor in C/Si heterojunction photovoltaic solar cells. In this letter, we report the rectifying current–voltage characteristics of the phosphorus-doped carbon/undoped-carbon (n-C/p-C) junction. The p- and n-carbon films were deposited by pyrolysis and ion-beam sputtering, respectively, on a p-Si substrate, using camphor as a natural carbon precursor. The preliminary photovoltaic characteristics of the cell reveals a short-circuit current density of 17.1 mA/cm2, open-circuit voltage of 0.339 V, and photoelectrical conversion efficiency of 1.82%, a reproducible result, under air mass zero and 1 sun illumination conditions. The spectral photoresponse characteristics of the cell of the above configuration was explained in terms of transmission/absorption characteristics of the two individual carbon layers.

Raman spectra of ion beam sputtered amorphous carbon thin films deposited from camphoric carbon

Abstract Thin films of carbon were deposited on single crystal silicon and quartz substrates by simple ion beam sputtering of camphoric carbon target, obtained from camphor: a natural source, at room temperature. The as-deposited films were heat treated at different temperatures and the effects of heat treatment on structural modifications were studied in detail by Raman spectroscopy through the evolution of D and G bands. The spectral evolution observed on heat treated samples show progressive formation of crystallites. These structural changes were further correlated with optical gap and fraction of sp 3 bonded carbons present, derived respectively from uv–visible and photoelectron spectroscopies, and the results obtained are discussed and compared with the literature.

Photovoltaic solar cell from camphoric carbon A natural source

Abstract Thin films of camphoric carbon, a natural source, have been deposited on a single crystal Si (1 0 0) surface, 2° off towards[0 1 1] and quartz/glass substrates, at room temperature, by both electron and ion beam deposition. The crystal structure, composition analysis, surface morphology and other optical properties of these films have been studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical and scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-visible reflectance/transmittance spectroscopy. Carbon photovoltaic cells have been made and our preliminary investigation of photovoltaic characteristics of a cell of configuration B-doped C (100 nm)/P-doped C (100 nm)/n-Si (380 μm) by electron beam deposition reveal short-circuit current of 1.2 mA cm−2 and an open circuit voltage of 102 mV with fill factor of 0.82, at AM1 condition. The low band gap (1 eV) and the semiconducting nature of these camphoric carbon films indicate the future scope of low-cost and high-efficiency carbon photovoltaic solar cells.

Determination of optical constants of solgel-derived inhomogeneous TiO 2 thin films by spectroscopic ellipsometry and transmission spectroscopy

Amorphous and nanocrystalline TiO(2) thin films coated on a vitreous silica substrate by a solgel dip coating method are investigated for optical properties by spectroscopic ellipsometry (SE) together with transmission spectroscopy. A method of analysis of SE data to determine the degree of inhomogeneity of TiO(2) films has also been presented. Instead of the refractive index, the volume fraction of void has been assumed to vary along the thickness of the films and an excellent agreement between the experimental and calculated data of SE below the fundamental band gap has been obtained. The transmission spectrum of these samples is inverted to obtain the extinction coefficient k spectrum in the wavelength range of 300-1600 nm by using the refractive indices and parameters of structure determined by SE. The nonzero extinction coefficient below the fundamental band-gap energy (3.2 eV) has been obtained for the nanocrystalline TiO(2) and shows the presence of optical scattering in the film.

Solar cells based on carbon thin films

Abstract Carbon as an alternative material for low-cost and high-efficiency solar cell is attempted. Thin films of semiconducting n- (p-doped) and p- (un-doped) type carbon have been deposited on various substrates by ion beam sputtering and pyrolysis, using camphor as a natural carbon precursor. The optical gap of carbon has been found to be around 1.05 and

Investigation of the effect of sol processing parameters on the photoelectrical properties of dye-sensitized TiO2 solar cells

Abstract Sol-gel spin-coating method has been explored to prepare nano-crystalline TiO2 films for dye-sensitized TiO2 solar cell application. Effects of evaporation temperature at which the sol is concentrated and addition of polyethelene glycol (PEG) to the sol at different concentrations on film thickness, surface morphology and solar cell performance are studied. Conversion efficiency is found to increase with PEG addition up to 40 % by weight of TiO2 and then decrease with further addition due to the development of cracks in the films. Higher conversion efficiency has been obtained with the sol concentrated at 40°C than at room temperature (30°C) after which it is found to decrease with increase in temperature due to higher degree of agglomeration caused by faster rate of evaporation. Further, it is observed that though the photocurrent and efficiency gradually increase with thickness at relatively lower thicknesses, a saturation in the photocurrent occurs at higher thicknesses.

Spectroscopic properties of nitrogen doped hydrogenated amorphous carbon films grown by radio frequency plasma-enhanced chemical vapor deposition

Nitrogen doped hydrogenated amorphous carbon thin films have been deposited by rf plasma-enhanced chemical vapor deposition using CH4 as the source of carbon and with different nitrogen flow rates (N2/CH4 gas ratios between 0 and 3), at 300 K. The dependence modifications of the optical and the structural properties on nitrogen incorporation were investigated using different spectroscopic techniques, such as, Raman spectroscopy, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, ultraviolet-visible (UV-VIS) spectroscopy, electron spin resonance (ESR), photoluminescence (PL) and spectroscopic ellipsometry (SE). Raman spectroscopy and IR absorption reveal an increase in sp2-bonded carbon or a change in sp2 domain size with increasing nitrogen flow rate. It is found that the configuration of nitrogen atoms incorporated into an amorphous carbon network gradually changes from nitrogen atoms surrounded by three (σ bonded) to two (π bonded) neighboring carbons with increasing nitrogen flo...

A phosphorous doped (n-type) carbon/boron doped (p-type) silicon photovoltaic solar cell from a natural source

In this letter we present our recent findings of photoelectrical properties of ion-beam-sputtered phoshorus doped camphoric carbon thin film deposited on a single crystal p-Di (100) surface, at room temperature. The effect of annealing on the photovoltaic properties such as power conversion efficiency and quantum efficiency of this n-C/p-Si heterojunction solar cell are outlined

Semiconducting camphoric carbon tubules

Semiconducting carbon tubules (n- and p-type) of band gap 1.96−1.98 eV have been synthesised from the soot of naturally occurring camphor for the first time. The mechanism of the formation of multichannel-multilayered camphoric tubules is discussed. Tubules are characterised by SEM, AFM, TEM, XRD, ESR, FTIR and electrical conductivity studies.