Ram Mohan Mehra | Sharda University (original) (raw)
Uploads
Papers by Ram Mohan Mehra
Progress in Photovoltaics, 2010
The influence of intensity and wavelength variation on the solar cell parameters of two different... more The influence of intensity and wavelength variation on the solar cell parameters of two different ZnO-based liquid state DSSCs named as Cell (A) ZnO/EosinY/LiI and Cell (B) ZnO/EosinY/LiBr was studied. It was found that Voc and Isc depend logarithmically and linearly on light flux, respectively, which indicates that light absorption and carrier diffusion do not limit the solar cell efficiency. The data was analyzed to ascertain the charge recombination mechanism between conduction band electrons and the electrolytes. The regeneration of dye due to I−/I3 and Br−/Br redox couple was examined by studying the wavelength dependence of IPCE. An estimation of series and shunt resistance is made using two methods: (i) different illumination method (ii) single I–V curve, for the two cells in order to understand the role of the electrolyte in controlling the solar cell parameters. Copyright © 2010 John Wiley & Sons, Ltd.
This paper reports optical properties of amorphous chalcogenide thin films of As2Se3 of different... more This paper reports optical properties of amorphous chalcogenide thin films of As2Se3 of different thicknesses 2000-6800Å. The transmittance and reflectance of thin films were measured in the wavelength range 500-1000 nm. It was found that the optical band gap increases with film thickness. Variation of refractive index n and extinction coefficient k with thickness have been studied to analyze optical efficiency of the As2Se3 thin films. The dielectric behavior of the films has also been studied and high frequency dielectric constants ε∞ has been estimated as a function of thickness of films.
This paper presents a study of photoconductivity of S- and Se-doped a-Si:H as a function of compo... more This paper presents a study of photoconductivity of S- and Se-doped a-Si:H as a function of composition and temperature. Temperature dependence of photoconductivity of the films was measured under the illumination of white light at 100~mW/cm2. The room temperature photoconductivity for the same doping concentration of 10-4 (to develop H2Se/SiH4 and H2S/SiH4) is found to be higher in Se-doped -- than S-doped -- a-Si:H film due to a low defect density. From the measurement of intensity dependence of photoconductivity, it is found that the addition of Se and S changes the recombination mechanism from monomolecular, for low-doped films, to bimolecular at higher levels of doping of Se and S.
The paper has reported the structural, transport and optical properties of boron doped zinc oxide... more The paper has reported the structural, transport and optical properties of boron doped zinc oxide (ZnO:B) thin films grown on glass substrate by sol-gel spin coating process. It is observed from the analysis of the X-ray diffraction (XRD) results that the crystalline quality of the films is improved with increasing B concentration. A crystallite size of ∼17 nm is obtained for B doped films. A minimum resistivity of 7.9×10 −4 Ω·cm is obtained at 0.6 at.% of B concentration in the ZnO:B films. Ionized and intragrain cluster scattering are found to dominate the scattering mechanism in ZnO:B films. Optical interference pattern in transmittance spectra shows good homogeneity with a transparency of ∼88% in the visible region. The band gap of the films is increased from 3.24 to 3.35 eV with increasing B concentration. Band gap widening is analyzed in terms of Burstein-Moss shift. The origin of the broad band photoluminescence (PL) spectra is explained in terms of the intragrain cluster scattering.
This paper reports the effect of thickness on the structural, morphological and optical propertie... more This paper reports the effect of thickness on the structural, morphological and optical properties of zinc oxide (ZnO) films. Thickness of ZnO films varied from 98 to 366 nm with an increase in the number of deposition cycles. Surface morphological studies showed that the increase in the film thickness causes an increase in the grain size. Roughness of the films has increased from 5.8 to 47 nm with an increase in the film thickness from 98 to 366 nm. The band gap is observed to vary from 3.33 to 3.24 eV with change in the film thickness from 98 to 366 nm. Thickness of the film affected the overall properties of the ZnO films significantly. The large surface roughness makes ZnO films to be potentially used as electrode in solar cells and gas sensing applications.
Progress in Photovoltaics, 2010
The influence of intensity and wavelength variation on the solar cell parameters of two different... more The influence of intensity and wavelength variation on the solar cell parameters of two different ZnO-based liquid state DSSCs named as Cell (A) ZnO/EosinY/LiI and Cell (B) ZnO/EosinY/LiBr was studied. It was found that Voc and Isc depend logarithmically and linearly on light flux, respectively, which indicates that light absorption and carrier diffusion do not limit the solar cell efficiency. The data was analyzed to ascertain the charge recombination mechanism between conduction band electrons and the electrolytes. The regeneration of dye due to I−/I3 and Br−/Br redox couple was examined by studying the wavelength dependence of IPCE. An estimation of series and shunt resistance is made using two methods: (i) different illumination method (ii) single I–V curve, for the two cells in order to understand the role of the electrolyte in controlling the solar cell parameters. Copyright © 2010 John Wiley & Sons, Ltd.
This paper reports optical properties of amorphous chalcogenide thin films of As2Se3 of different... more This paper reports optical properties of amorphous chalcogenide thin films of As2Se3 of different thicknesses 2000-6800Å. The transmittance and reflectance of thin films were measured in the wavelength range 500-1000 nm. It was found that the optical band gap increases with film thickness. Variation of refractive index n and extinction coefficient k with thickness have been studied to analyze optical efficiency of the As2Se3 thin films. The dielectric behavior of the films has also been studied and high frequency dielectric constants ε∞ has been estimated as a function of thickness of films.
This paper presents a study of photoconductivity of S- and Se-doped a-Si:H as a function of compo... more This paper presents a study of photoconductivity of S- and Se-doped a-Si:H as a function of composition and temperature. Temperature dependence of photoconductivity of the films was measured under the illumination of white light at 100~mW/cm2. The room temperature photoconductivity for the same doping concentration of 10-4 (to develop H2Se/SiH4 and H2S/SiH4) is found to be higher in Se-doped -- than S-doped -- a-Si:H film due to a low defect density. From the measurement of intensity dependence of photoconductivity, it is found that the addition of Se and S changes the recombination mechanism from monomolecular, for low-doped films, to bimolecular at higher levels of doping of Se and S.
The paper has reported the structural, transport and optical properties of boron doped zinc oxide... more The paper has reported the structural, transport and optical properties of boron doped zinc oxide (ZnO:B) thin films grown on glass substrate by sol-gel spin coating process. It is observed from the analysis of the X-ray diffraction (XRD) results that the crystalline quality of the films is improved with increasing B concentration. A crystallite size of ∼17 nm is obtained for B doped films. A minimum resistivity of 7.9×10 −4 Ω·cm is obtained at 0.6 at.% of B concentration in the ZnO:B films. Ionized and intragrain cluster scattering are found to dominate the scattering mechanism in ZnO:B films. Optical interference pattern in transmittance spectra shows good homogeneity with a transparency of ∼88% in the visible region. The band gap of the films is increased from 3.24 to 3.35 eV with increasing B concentration. Band gap widening is analyzed in terms of Burstein-Moss shift. The origin of the broad band photoluminescence (PL) spectra is explained in terms of the intragrain cluster scattering.
This paper reports the effect of thickness on the structural, morphological and optical propertie... more This paper reports the effect of thickness on the structural, morphological and optical properties of zinc oxide (ZnO) films. Thickness of ZnO films varied from 98 to 366 nm with an increase in the number of deposition cycles. Surface morphological studies showed that the increase in the film thickness causes an increase in the grain size. Roughness of the films has increased from 5.8 to 47 nm with an increase in the film thickness from 98 to 366 nm. The band gap is observed to vary from 3.33 to 3.24 eV with change in the film thickness from 98 to 366 nm. Thickness of the film affected the overall properties of the ZnO films significantly. The large surface roughness makes ZnO films to be potentially used as electrode in solar cells and gas sensing applications.