Bhaskar Parida

Enhanced photocurrent of Si solar cell with the inclusion of a transparent indium tin oxide thin film

We investigated the enhanced photocurrents in crystalline Si solar cells with the inclusion of indium tin oxide thin film. The indium tin oxide enhances the quantum efficiency and reduces photoreflectance in the spectral region of 310–1048 nm. The enhanced photocurrent is ranged at the Si band edge for the spectral peak near 1033 nm. For the subband gap region, the photocurrent is strongly reduced by the indium tin oxide thin film, indicating that the transmission of infrared spectra was prevented by plasmonic metamaterial effect. The fabricated cell showed the short circuit current density enhanced due to the carrier excitation behavior at conduction band of the infrared spectra induced metallic indium tin oxide thin film. The enhanced shunt resistance of the pn junction is related to the blocking of Ag paste penetration into the Si emitter layer by the indium tin oxide thin film during fabrication process.

Enhanced visible light absorption by 3C-SiC nanoparticles embedded in Si solar cells by plasma-enhanced chemical vapor deposition

Solar cells with 3C-SiC nanoparticles embedded in the Si were investigated by plasma-enhanced chemical vapor deposition. Several sizes of SiC nanoparticles were used as the intermediate layer for the solar cell. The Si thin films showed the formation of microand nanocrystallites on the SiC nanoparticle sites, which play an important role of heating block as a nanosubstrate. The Raman spectra revealed that the SiC nanoparticles were embedded in mixed phases of amorphous and nanocrystalline Si. Compared to the conventional solar cell sample, the photoreflectance was significantly reduced in the UV/visible spectral region due to the presence of the embedded 3C-SiC nanoparticles. The Si nanocrystals formed by the thin film deposition played an important role in reducing the photoreflectance within the visible to infrared spectral zones. Furthermore, the SiC nanoparticles contributed less in the photoabsorption at a longer infrared spectral zone wavelength of 1200 nm.

Nanopyramid Formation by Ag Metal-Assisted Chemical Etching for Nanotextured Si Solar Cells

Copyright ©2015 KIEEME. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN: 1229-7607 eISSN: 2092-7592 DOI: http://dx.doi.org/10.4313/TEEM.2015.16.4.206 OAK Central: http://central.oak.go.kr

Nanotextured Si Solar Cells on Microtextured Pyramidal Surfaces by Silver-assisted Chemical Etching Process

We investigated nanotextured Si solar cells using the silver-assisted chemical etching process. The nanotexturing process is very sensitive to the concentration of chemical etching solution. The high concentration process results in a nanowire formation for the nanosurfaces and causes severe surface damage to the top region of the micropyramids. These nanowires show excellent light absorption in photoreflectance spectra and radiative light emission in photoluminescence spectra. However, the low concentration process forms a nano-roughened surface and provides high minority carrier lifetimes. The nano-roughened surfaces of the samples show the improved electrical cell properties of quantum efficiency, conversion efficiency, and cell fill factor due to the reduction in the formation of the over-doped dead layer.

Oxidation behavior with quantum dots formation from amorphous GaAs thin films

ABSTRACT We investigated the oxidation behaviour of an amorphous GaAs thin film deposited onto a micro/nanotextured Si surface by an electron beam. After the deposited film was exposed to air, microcrystallites were formed with octahedral cubic and monoclinic structures of arsenic oxides. Short time exposure after thin film deposition showed the formation of cubic arsenolite while long time exposure showed the formation of monoclinic claudetites as well as cubic arsenolites. These oxide microcrystallites at the GaAs thin film surface disappeared after the sample annealing process. However, the amorphous GaAs thin film included high-density GaAs nanodots. From UV and inverse photoemission spectroscopies, the thin film showed n-type band structure with an energy gap of 2.73 eV. Photoluminescence measurement showed an emission peak at (450–513) nm with the energy of (2.41–2.75) eV corresponding to dot size of (4.1–4.5) nm.

Effect of hydrogen defects on nanocrystallite layers of Si solar cells by hydrogen implantation

The Si solar cells were irradiated with high energy hydrogen ions of 10, 30, 60 and 120 keV at the dose rate of 1017 H+ ions (proton)/cm2. The structural, optical and electrical properties of the implanted samples and fabricated cells were studied. The implantation induced defects bringing structural changes before and after annealing was evidenced by the transmission electron microscopy. The Raman spectrum showed a change of crystalline to amorphous state at 480 cm−1 when the sample was implanted by hydrogen ion of 30 keV energy. Formation of nanocrystallite layers were observed after annealing. The electroluminescence images showed that hydrogen-related defect centers were involved in the emission mechanism. The photoluminescence emission from the implanted cells was attributed to nanocrystallite layers. From current–voltage measurements, the conversion efficiencies of implanted Si solar cells were found lower than the un-implanted reference cell. The ion implantation did not passivate the defects rather acted as recombination centers.

Nanoporous Anodic Edge Passivation of Si Solar Cells.

We investigated the anodization effect on edge passivation of Si solar cells. The Si anodization allowed SiO2 formation on the edges of the cell for electrical passivation. The edge passivated cell showed enhanced conversion efficiency with reduced carrier recombination which was observed from photoluminescence and electroluminescence images. The luminescences were reduced at the edges indicating prevention of edge current leakage. However, when the rear Al paste layer of a sample was contacted to the solution during the anodization process, the conversion efficiency of the cell was reduced. We characterized oxide thin films by performing the anodization process for front Al thin film layer deposited by evaporation and rear Al paste layer. The front anodic aluminum oxide covering the Si emitter layer showed the excellent phototransmission with small photoreflectance lower than 5% and the anodization of Al paste showed the formation of a thin SiO2 film as well as nanoporous Al2O3 layer originating from the microspherical Al paste. The rear Al paste anodization allowed the Al microspheres to be filled with the nanopores in the inner empty space.

Enhancement effect of short-circuit currents of Si solar cells with inclusion of indium tin oxide layers on metal–semiconductor interfaces

We investigated the enhancement effect on short-circuit currents by indium tin oxide contact layers imbedded in metal–semiconductor interfaces in Si solar cells. Both samples that incorporate the thin film layer and the crossed finger lines of indium tin oxide exhibit an enhancement of p–n junction photocurrents and depletion capacitances with enhanced bulk donor concentrations at the emitter contacts. The indium tin oxide layer provides the passivation layer on the Si emitter surface with reduced trap states and the carrier transport layer for charge collection. The Si solar cells with indium tin oxide showed improved performance in shunt resistance and short-circuit current.