Degradation modeling of InGaP/GaAs/Ge triple-junction solar cells irradiated with various-energy protons

Degradation modeling of InGaP/GaAs/Ge triple-junction (3J) solar cells subjected to proton irradiation is performed with the use of a one-dimensional optical device simulator, PC1D. By fitting the external quantum efficiencies of 3J solar cells degraded by 30 keV, 150 keV, 3 MeV, or 10 MeV protons, the short-circuit currents (I_SC) and open-circuit voltages (V_OC) are simulated. The damage coefficients of minority carrier diffusion length (K_L) and the carrier removal rate of base carrier concentration (R_C) of each sub-cell are also estimated. The values of I_SC and V_OC obtained from the calculations show good agreement with experimental values at an accuracy of 5%. These results confirm that the degradation modeling method developed in this study is effective for the lifetime prediction of 3J solar cells.     

Preparation of magnetic fluid having active-gas resistance and ultra-low vapor pressure for magnetic fluid vacuum seals

The magnetic fluid, having an ultra-low vapor pressure property of 7·0×10⁻¹⁰ Pa at 293 K, was prepared. Hexafluoropropylene oxide polymer oil having high molecular weight was used as base oil. Magnetic particles were dispersed by using two types of new designed and synthesized hexafluoropropylene oxide acid derivative surfactants. The obtained magnetic fluid had a saturation magnetization of 35·0 mT, its magnetite particles were dispersed stably and showed a superior resistance to active gasses. It was ascertained that the magnetic fluid vacuum seal using the prepared fluid had the ultra high vacuum performance.     

Adsorption behaviors of mercury from aqueous solution using sulfur-impregnated adsorbent developed from coal

Adsorption of mercury from aqueous solution on sulfur-impregnated adsorbent has been studied. Raw coal was mixed with K₂S powder, and then heated at 800-1000 °C for 30 min in nitrogen to produce sulfur-impregnated adsorbent. The sulfur content and specific surface area of the adsorbent were determined, and the ability of the adsorbent to adsorb mercury in aqueous solution was examined. With increasing temperature of sulfur-impregnation, specific surface area of the adsorbent increases, while sulfur content of the adsorbent is almost constant. The adsorbent obtained at 900 °C shows the highest and fastest adsorption of mercury from aqueous solution at 25 °C, and the elution extents of adsorbed mercury are negligible in distilled water and 10% in 0.1 M HCl solution, respectively. Adsorption kinetics was tested for pseudo-first order and pseudo-second order reactions, and the rate constants of adsorption for these kinetic models were calculated. Adsorption experiments demonstrate that the adsorption process corresponds to pseudo-second-order kinetic model than pseudo-first-order model. With increasing temperature of aqueous solution, the kinetics of adsorption becomes faster and the amount of mercury adsorbed on the adsorbent increases. The thermodynamic values, ΔG⁰, ΔH⁰ and ΔS⁰, indicated that adsorption was an endothermic and spontaneous process.     

Image Compression by Layered Quantum Neural Networks

We have proposed the qubit neuron model as a new scheme in non-standard computing. Identification problems have been investigated on neural networks constructed by this qubit neuron model, and we have found high processing abilities of them. In this paper, we evaluate the performance of the quantum neural network of large size in image compression problems to estimate the utility for the practical applications comparing with the conventional network consists of formal neuron model.     

Selection of rare earth silicates for highly scaled gate dielectrics

An aggressive equivalent oxide thickness (EOT) scaling with high-k gate dielectrics has been demonstrated by ultra-thin La₂O₃ gate dielectric with a proper selection of rare earth (La-, Ce- and Pr-) silicates as an interfacial layer. Among silicates, Ce-silicate has shown the lowest interface-state density as low as 10¹¹ cmv⁻²/eV with a high dielectric constant over 20. n-Type field-effect transistor (FET) with a small EOT of 0.51 nm has been successfully fabricated with a La₂O₃ gate dielectric on a Ce-silicate interfacial layer after annealing at 500 °C. Negative shift in threshold voltage and reduced effective electron mobility has indicated the presence of fixed charges in the dielectric. Nonetheless, the high dielectric constant and nice interfacial property of Ce-silicate can be advantageous for the interfacial layer in highly scaled gate dielectrics.     

PL and PLE studies of KMgF3:Sm crystal and the effect of its wavelength conversion on CdS/CdTe solar cell

We studied the effect on conversion efficiency of a CdS/CdTe solar cell by applying a wavelength conversion of a rare earth ion. Both photoluminescence (PL) and photoluminescence excitation (PLE) spectra of the Sm-doped KMgF₃ crystal were investigated. As a result, we found that both the divalent and the trivalent Sm ions coexist in the grown KMgF₃ crystals. Also, all the PLE spectra below 500 nm were effectively converted to PL spectra above 540 nm and the solar cell possessed a high spectral response. The quantum efficiency of Sm ions was estimated to be 0.84 from the comparison of the experimental curve with the calculated one for the increased spectral response below 500 nm. When a thin disc crystal of KMgF₃:Sm was placed on the top of CdS/CdTe solar cell as a precursor for wavelength conversion, both the maximum output power and the conversion efficiency increased by 5% as compared with the case of a pure KMgF₃ crystal.     

Application of rare-earth complexes for photovoltaic precursors

By applying rare-earth complexes as photovoltaic precursors, the conversion efficiency of solar cells were improved. Rare-earth complexes absorb light at shorter wavelengths and subsequently emit light at longer wavelengths. The high-energy region of the solar spectrum is shifted to longer wavelengths, hence the cell-output power is higher because the emitted light matches with a higher sensitivity region of the basic Si solar cell. For a CaF₂:Eu single crystal placed on top of an a-Si solar cell experiments showed a maximum relative conversion efficiency of 1.5 Eu ions in CaF₂---SrF₂ mixed crystals, whose emission is even more red-shifted compared with CaF₂ crystals, showed slight improvements. The ion implantation of rare-earth ions into CaF₂ evaluated potential application for antireflection (AR) coatings. Futhermore, porous glass doped with Eu-chelete complexes have been investigated.