Satoshi Yamanaka

Study of CuInSe2 Formation Kinetics in the Selenization Process by Raman Spectroscopy

Formation kinetics of polycrystalline CuInSe2 films in selenization of Cu/In/Se stacked layers was studied using Raman spectroscopy. Raman spectra of the films clearly show a structural change of the film at elevated temperatures. It is concluded that Cu is selenized preferentially at low temperatures around 200°C and that the CuInSe2 phase is formed at temperatures above 250°C.

Characterization of Copper Indium Diselenide Thin Films by Raman Scattering Spectroscopy for Solar Cell Applications

Compositional characterization of CuInSe2 thin films by Raman scattering spectroscopy for solar cell applications was proposed. It was shown that Raman scattering spectroscopy is a promising method for the characterization of CuInSe2 film composition (especially Cu/In ratio). It was also found by using Raman scattering spectroscopy that the In-rich CuInSe2 on Cu-rich p+-CuInSe2 bilayer structure gives high-photovoltaic performance, and a conversion efficiency of 8.16% for CdS/CuInSe2 solar cells was achieved by optimizing such a bilayer structure.

High-Performance Hydrogenated Amorphous Silicon-Germanium Solar Cells Fabricated by Photochemical Vapor Deposition

High-quality a-SiGe:H films have been prepared by photochemical vapor deposition (photo-CVD) with a high dilution ratio of H2. Films with a bandgap of 1.55 eV has a photoconductivity of 1.6×10-4 S/cm (AM1, 100 mW/cm2). Solar cells of the p-i-n type were fabricated by applying such high-quality a-SiGe:H films to the i-layer. The performance of a-SiGe:H solar cells has been drastically improved by introducing graded-bandgap layers at the p/i and i/n hetero-interfaces. At present, a conversion efficiency of 8.65% with high collection efficiencies in the long-wavelength region has been achieved with 1.57 eV bandgap material.

Numerical Study of Amorphous Silicon Based Solar Cell Performance Toward 15% Conversion Efficiency

A detailed theoretical analysis of a-Si based solar cells has been performed using a comprehensive computer simulation model in order to clarify the factors limiting the cell performance. We simulated how the solar cell characteristics are influenced by the variations of various factors. As a result, it was found that the solar cell performance was seriously affected by low conductivity in the a-SiC p-layer and the density of D-states in the i-layer. Based on all of the theoretical results, we predict that a conversion efficiency of over 15% can be potentially realized for the a-Si based single-junction solar cell when the enhancement of the carrier concentration in the p-layer (greater than 1018 cm-3) and the decrease of the density of D-states in the i-layer (to about one fifth of the present state-of-the-art value) are achieved and the device structure is optimized.

Raman scattering study of CuInSe/sub 2/ films prepared by three-source RF-sputtering and by selenization of Cu/In/Se stacked layers

CuInSe/sub 2/ thin films prepared by three-source RF-sputtering and selenization of Cu/In/Se stacked layers were characterized by Raman spectroscopy. The crystallinity of polycrystalline thin film CuInSe/sub 2/ was accurately evaluated from their Raman spectra. The films with good crystallinity and uniform large-size grains show a very sharp peak at 174 cm/sup -1/ in the Raman spectra. The Raman spectroscopy was found to be a good technique to study formation of the CuInSe/sub 2/ chalcopyrite phase in the selenization process. The formation of the CuInSe/sub 2/ chalcopyrite phase occurs at the critical temperature, slightly above 250 degrees C.<<ETX>>

Theoretical investigation of the optimum design for amorphous silicon based solar cells

A detailed theoretical analysis of a-Si-based solar cells has been performed using a computer simulation model in order to clarify the factors limiting cell performance. It was found that the solar cell performance was affected by low conductivity in the p-layer and the density of D states in the i-layer. The simulation model predicted that the upper limit of a-Si solar cell efficiencies is about 15.0%, which could be obtained for a highly conductive p-layer with a carrier concentration of approximately 10/sup 18/ cm/sup -3/ and high-quality a-Si having a low density of D states (1*10/sup 15/ cm/sup -3/). It also predicted an optimum bandgap of the i-layer of 1.5 eV, assuming that the N/sub DB/ of the i layer is constant with bandgap energy.<<ETX>>

Effect of δ-doped p-layer on the photovoltaic properties of a-Si solar cells

Abstract The optical and electrical properties of a-SiC p-layer were improved by applying the δ-doping technique. It was demonstrated that the δ-doped p-layer successfully enhances the Voc and the performance of a-Si solar cells. It was also shown using computer simulation that the effect of the δ-doped p-layer is due to the increase of the in-plane acceptor concentration in the p-layer.

High efficiency amorphous silicon solar cells with 'Delta-doped' p-layer

Novel amorphous silicon solar cells with sigma -doped p layers have been fabricated. The boron concentration in the sigma -doped p layer has been measured by secondary ion mass spectrometry. A peak boron concentration of 2*10/sup 21//cm/sup 3/, which is one or two orders of magnitude larger than that of a conventional a-Si p layer, has been obtained. A conversion efficiency of 11.5% has been obtained for a solar cell with the sigma -doped p layer.<<ETX>>