Hajimu Sonomura

Structural and Electrical Properties of Chemical-Solution-Deposited CdS Films for Solar Cells

The structural and electrical properties of CdS films prepared by chemical-solution deposition have been studied. As-deposited films have about 0.4 µm thickness, a grain size of about 0.3 µm and consist of the coalesence of columnar structure. The dark resistivity of more than 104 Ωcm of as-deposited films decreased by about three orders of magnitude to about 10 Ωcm upon annealing in N2 atmosphere at 300–500°C for 20 minutes. The decrease in resistivity was caused by an increase in electron concentration. The resistivity of annealed CdS films was low enough to use as a window layer of thin-film solar cells.

Effect of Substrate Temperature on the Photovoltaic Properties of a CdS/CdTe Solar Cell

Structural and electrical properties of CdTe thin films prepared by the conventional vacuum evaporation method were studied. Photovoltaic properties of thin-film CdS (chemical-solution-deposited)/CdTe (vacuum-evaporated) solar cells were also investigated. The crystal structure of CdTe films deposited on the CdS films at the substrate temperature of 300~520°C was of the zincblende type with a preferential orientation of the (111) plane parallel to the substrate. The dark resistivity of the CdTe films deposited on the glass substrates was about 107 Ωcm. Illumination caused the resistivity decrease of the films by about two orders of magnitude. The conversion efficiency of the CdS/CdTe solar cells increased with increasing substrate temperature. The present thin-film CdS/CdTe solar cell showed a conversion efficiency of greater than 5%.

Annealing effect of Cu2TeAu contact to evaporated CdTe film on photovoltaic properties of CdS/CdTe solar cell

Abstract The annealing effect of an evaporated Cu 2 TeAu contact to CdTe film on the photovoltaic properties of thin-film CdS/vacuum-evaporated CdTe solar cells has been investigated. V oc and J sc for the cells with Cu 2 TeAu contact increased greatly with increasing annealing temperature and showed a maximum value at around 250. Photovoltaic properties of the cell with Cu 2 TeAu contact were improved by annealing in a greater extent than those of the cell with TeAu or TeCu contacts. The cells with Cu 2 TeAu contact exhibit a higher conversion efficiency, comparing with the cells with TeAu or TeCu contacts. The cell with Cu 2 TeAu contact showed a conversion efficiency of 10%. Cu 2 TeAu contact acts as the best pseudoohmic contact on vacuum evaporated CdTe film.

Transient Current Dependent on Nematic Director Orientation

Abstract Transient currents induced by the polarity reversal of an applied DC voltage in nematic liquid crystals have been studied experimentally and theoretically. The experimental results of transient currents in the cells with various treated substrate surfaces have been presented. In the theoretical studies, the presence of adsorbed charge layers on the substrate surfaces and a spatial distribution of carrier mobility dependent on a director orientation have been assumed. By one dimensional mobility distribution of drift sheet carrier across the cell, the carrier transport process and the generation mechanism of the transient current with or without peaks can be well understood. The experimental results on transient currents have been successfully explained from the interpretation of the different adsorbed charge ratio which is the ratio of adsorbed charges to the total amount of the charges in the cell.

Synthesis and Some Properties of Solid Solutions in the GaP-ZnS and Gap-ZnSe Pseudobinary Systems

Solid solutions of heterovalent systems, GaP-ZnS and GaP-ZnSe are prepared by the solution growth method. The energy gaps determined by optical absorption vary anomalously with composition. Measurements of photoconductivity and photovoltaic effect support the validity of the energy gap values determined by the absorption. The resistivities of the solid solutions are extremely large except for GaP-rich alloys. Photoluminescent spectra are closely related to deep recombination centers. The attempt to obtain a material having a direct wide energy gap and controllable electrical properties is unsuccessful because of anomalous composition dependences of the energy gap and the resistivity in the solid solutions studied here.

Screen printed CdS/CdTe cells for visible-light-radiation sensor

Thick-film CdS/CdTe photovoltaic cells have been prepared on borosilicate glass substrates by sequential screen printing and sintering steps. The residual amount of acts as a flux in a sintered CdS film and the sintering temperature of the CdTe film has a strong influence on the spectral response of the cell. The cells fabricated with the sintered CdS film having a larger amount of residual Cl ion and the cells sintered at a higher temperature show a poor response in the short wavelength. This is due to a formation of solid solution at the CdS/CdTe interface during the CdTe sintering. The screen printed CdS/CdTe cells also exhibit a higher spectral sensitivity in the longer wavelength region compared with typical CdS/CdTe cells. This may be due to the narrowing of the band gap resulting from layer. The cells prepared under suitable conditions show a spectral sensitivity nearly constant in the range of 530 to 850 nm. cell has shown an increase in the spectral response at 500 nm wavelength region. These cells may be used as a visible-light-radiation sensor with a constant sensitivity in a wider wavelength region.

Te-metal Contact on Evaporated CdTe Film for a CdS/CdTe Solar Cell

Abstract The photovoltaic properties of thin-film CdS/vacuum-evaporated CdTe solar cells with evaporated TeAu and TeCu contacts to the CdTe film have been investigated. The contact properties were improved by annealing at 350°C and 240°C, respectively, for the cell with pinhole-free CdTe film. The improvement of the cell performance was achieved for an about 1 μm thick CdTe cell with TeAu contact and for a 2–4 μm thick CdTe cell with TeCu contact. The Te film of TeAu contact may prevent the CdS film from touching Au or diffused Au through pinholes in thin CdTe film. The optimum thickness of the Te film for improving the cell performance depends on the thickness of the CdTe film for the cell with TeCu contact.

Properties of CdS/CdTe Solar Cells with Cu2Te–Au Contacts

Cu2Te-based contact layers are annealed onto CdTe films of CdS/CdTe solar cells. The photovoltaic properties of cells with Cu2Te–Au contacts are greatly improved when the annealing temperature was increased. The V oc and J sc of the cells reached a maximum value at around 250° C. An increase in the spectral response of the short wavelength region was observed for cells with thinner CdS films. CdS/CdTe solar cells with Cu2Te–Au contacts had a conversion efficiency of 10.5%.

Spin-dependent luminescence enhanced by interface stress between III-V alloy layers on excitation of circularly polarized light

The relation between the luminescence polarization for circularly polarized light and the band structure of zincblende semiconductor under two-dimensional stress is theoretically discussed. Two type of samples with an unstrained InP layer and a strained InP layer due to the lattice mismatch are prepared. The luminescence from the InP layer excited by circularly polarized light is analyzed using a Babinet-Soleil compensator, (or phase-modulator) and polarizer. The large luminescence polarization of circularly polarized light is observed in the strained sample. At temperatures below 60 K, the luminescence polarization exceeds 25% which is the maximum value predicted in the unstrained crystal. The experimental results show that the luminescence polarization is increased by the internal strain due to the lattice mismatch.

A New Method for Measuring Optical Activity in Crystals and Its Application to Quartz

This report describes a theoretical study of a convenient method for measuring the optical activity in crystals in which birefringence and optical activity coexist. The method was applied to right-handed quartz. The gyrations in the [100] direction and at 45° from the optical axis were measured. The gyration tensor component g33 calculated from the gyrations measured in these two directions was found to be in good agreement with the value of g33 measured by other workers in the direction of the c-axis (the optical axis) by conventional methods.