Toshio Hama

Effects of Surface Morphology of Transparent Electrode on the Open-Circuit Voltage in a-Si:H Solar Cells

The open-circuit voltage of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells depends on the surface morphology of transparent electrodes and the i-layer thickness. We have studied the relationship between the Voc and these parameters experimentally. To investigate the detailed mechanism of the Voc drop, transmission and scanning electron microscopies (TEM and SEM) were used, and it was found by the TEM images that white stripelike defective regions were generated in the i-layer deposited on highly textured transparent electrodes. From the current-voltage characteristics of these solar cells under the dark condition, the relationship between the defects and the electrical properties of the cells has been studied. The results showed that the defect acts as a recombination center of carriers.

An electroluminescence device for printable electronics using coprecipitated ZnS:Mn nanocrystal ink

Electroluminescence (EL) devices for printable electronics using coprecipitated ZnS:Mn nanocrystal (NC) ink are demonstrated. The EL properties of these devices were investigated along with the structural and optical properties of ZnS:Mn NCs with an emphasis on their dependence on crystal size. Transmission electron microscopy and x-ray diffraction studies revealed that the NCs, with a crystal size of 3-4 nm, are nearly monodisperse; the crystal size can be controlled by the Zn(2+) concentration in the starting solution for coprecipitation. The results of optical studies indicate the presence of quantum confinement effects; in addition, the NC surfaces are well passivated, regardless of the crystal size. Finally, an increase in the luminance of EL devices with a decrease in crystal size is observed, which suggests the excitation mechanism of ZnS:Mn NC EL devices.

Hydrogen content dependence of the optical energy gap in a-Si:H

Abstract A theoretical attempt has been made on the hydrogen content dependence of the optical energy gap in a-Si:H using a simple tight-binding model. The interband optical absorption coefficient is calculated by CPA. It has been shown that energy spectra of the joint density of states shift to the higher energy side in parallel with increasing hydrogen content. For the comparison with the realistic line shape of experimentally observed absorption spectra, the effect of the Lorentzian distribution of the SiH bond states is examined.

Creation and saturation of light-induced defects in a-Si:H

Abstract The saturation behavior of the light-induced defects in a-Si:H has been investigated. The saturation of the light-induced defects is shown to come from the limited density of sources for the light-induced defects. The sources for the light-induced defects are supposed to be weak Si:Si bonds the density of which decrease with increasing deposition temperature.

Electrical and structural properties of a-SiGe:H films

Abstract The good-quality a-SiGe:H is produced in a triode rf glow discharge system from SiH 4 +GeH 4 mixture. This a-SiGe:H possesses very sharp Urbach tail (Urbach energy E 0 =50meV) and better photoelectrical properties as compared with films produced in a conventional diode system. It is also shown that an inhomogeneous microstructure is observed in a-SiGe:H films with poor photoelectrical properties.

Light-induced recovery of a-Si solar cells

The light-induced recovery in efficiency of amorphous silicon (a-Si) solar cells has been studied. The recovery of solar cells degraded by a concentrated light-soaking was accelerated under 1 sun illumination as compared with that in the dark. A similar phenomenon has been observed under current injection. The kinetics of light-induced annealing has been discussed on the basis of a series of the experiments.

Effects of deposition temperature and hydrogen evolution on light-induced defects in a-Si:H

Abstract To clarify the role of hydrogen in the Staebler-Wronski effect of a-Si:H, we have studied the effects of hydrogen incorporation and evolution on the light-induced changes in photoconductivity and spin density of a-Si:H. Our results suggest that the light-induced defects in a-Si:H are created through the breaking of weak SiSi bonds in the regions containing clustered hydrogen which effuses at low annealing temperature.

Structural study of p-type μc-Si layer for solar cell application

Abstract It is important for solar cell application to study the opto-electrical properties of very thin (

Formation of CuIn(Ga)Se2 Thin Films by Selenization and Application to Solar Cells

Preparation conditions of device-quality CuInSe2 (CIS) and CuIn1-xGaxSe2 (CIGS) thin films were studied. We formed CIS and CIGS films by annealing different types of precursor films, such as Gu/In stacked films and Cu–In–Se co-deposited films, under H2Se atmosphere. We obtained CI(G)S films with large grain size using precursors prepared at 200°C. The grain sizes of CI(G)S film using stacked precursors were larger than those using co-deposited precursors. Use of co-deposited precursors reduced formation of MoSe2 at Mo/CI(G)S boundary during selenization process. Fill-factor (FF) exceeding 0.7 was obtained for CIS cells using co-deposited precursors prepared at substrate temperature of 200°C.