Materials Science Forum Vol. 725

Abstract: We focused on the reduction of the crack formation in the transfer of the Cu(In,Ga)Se₂ (CIGS) thin film solar cell structure. We found that the crack formation was reduced by increasing the In₂O₃:Sn thickness. We concluded that the whole thickness of the transferred layers is an important roll in the reduction of the crack formation. Moreover, we proposed the crack occupancy as a quantitative evaluation method of the crack inside the CIGS layer.

Abstract: We proposed a modified 3-diode equivalent circuit model with an inverted diode for the analysis of the characteristics of bulk hetero junction organic solar cells before and after heat treatment with the reverse bias of -8 V. The dark current density-voltage (J-V) characteristics of the bulk hetero junction organic solar cells before and after heat treatment were measured. From dark J-V characteristics of each organic solar cell, fitting of J-V curve between measured and calculated date was carried out using a modified 3-diode equivalent circuit model with an inverted diode. Using extracted diode parameters, the performances of the bulk hetero junction organic solar cells were compared and evaluated. The measured and calculated J-V characteristics of the bulk hetero junction organic solar cell agreed well, and the organic solar cells were able to be evaluated using the proposed method.

Abstract: Under the concentration conditions, it is important to optimize the design of electrodes and cell structures, because the high density energy is emitted to the cell and photocurrent with high density is generated by each subcell of multi-junction solar cell. The in-plane distributions of power consumption due to the each resistance component were calculated by using total 3D simulator. In the case of optical design without homogenizer, local power consumptions due to the electrode resistance were observed at a part of cell. On the other hand, in the case of optical design with homogenizer, the power consumption was considerably reduced. This technique can be applied to the structural optimization of solar cells for concentration.

Abstract: For the development of concentrator photovoltaic (CPV) module realizing high efficiency, it is necessary to achieve the high efficiency optical system including Fresnel lens and homogenizer. For the improvement of optical systems, it is very important to understand the contribution of the light irradiated to a localized position on the Fresnel lens. The light beam induced current (LBIC) system was constructed to evaluate the focusing characteristic of the CPV module. We locally irradiated a light from solar simulator to the CPV mini-module and measured the generation current, and the localized characteristics were represented by two-dimensional mappings. Moreover, we evaluated the influence of tracking error by changing the irradiation angle. In the case of tracking errors, the peak of generated current was shifted and the current was decreased. In the case of tracking error of 1.0 o, the total generated current was reduced 12%, in comparison with the normal irradiance.

Abstract: Using the peculiar behavior of nitrogen molecules in FZ silicon crystals contained with a high concentration of vacancies, this paper describes the following four important values: the estimated vacancy concentrations, the deep levels at 0.44 eV under the conduction band for n-type and at 0.66 eV over the valence band for p-type for mono vacancies and the diffusion coefficient of the silicon interstitials DI-FZ = 1.3×exp(-4.5 eV/kT).

Abstract: Silicon polymorphs have been prepared by means of scratching or indentation of Si(100) surfaces. Different indenter types have been used in order to validate the independence of silicon polymorph formation from indenter geometry. The formation of silicon polymorphs could be verified by registering the loading-displacement curves. Related to the maximum loads applied, only the formation of the meta-stable silicon phases SI-III, Si-IV and Si-XII has been observed, what has been verified by Raman spectroscopy. Four different ways of the preparation of electron transparent samples are presented and compared. Finally, a first electron energy loss spectrum of certain silicon polymorphs is shown.

Abstract: Optical tools such as infra-red absorption, photoluminescence, or Raman spectroscopy have been used for decades to observe the localized vibrational modes associated with impurities in semiconductors. The frequencies of these modes slightly shift with the isotope of the impurity while host-atom isotopes often show up as shoulders in the spectra. These shifts and shoulders are precious indicators of the nature of the defect. But sometimes, very small isotope-related frequency shifts cause very large changes in vibrational lifetimes. Impurity-isotope effects have now been predicted to impact the thermal conductivity of semiconductors containing a few atomic percent of impurities. Impurity isotope effects can be surprisingly large.

Abstract: Formation and annealing behavior of the 1.014-eV copper center and its dissociation product (center) in silicon are characterized by photoluminescence (PL) and deep-level transient spectroscopy (DLTS) measurements. On the basis of the findings reported in this study, the structures of the centers are discussed.

Abstract: We have observed five electron traps with energy levels at 0.16, 0.30, 0.40, 0.53 and 0.67 eV below the conduction band in Pd and H doped Si by DLTS technique. Successive annealing at 373 K and 473 K for 30 min respectively caused two levels at Ec-0.16 eV and Ec-0.67 eV to disappear and simultaneously a new level to emerge at Ec-0.19 eV. From such annealing behavior and the comparison of the energy levels observed in the present study with those in the literature, we assign them to various Pd and H related defects as follows, Pd-H2: Ec-0.16 eV and Ec-0.67 eV, Pd acceptor: Ec-0.19 eV, Pd-H3: Ec-0.30 eV, Pd-H1: Ec-0.40 eV.

Abstract: For the B-doped silicon crystals grown with and without N-doping, we measured the temperature dependence of the elastic constant in low-temperature region, to examine whether the N-doping annihilates the elastic softening caused by the gap-states of the isolated single vacancy. We have found that the elastic softening clearly observed for the N-free crystals is not observed for the N-doped ones, suggesting that the gap-states of the vacancies causing the elastic softening are destroyed by the N-doping. This is consistent with the model of Abe [T. Abe, J. Crystal Growth, 327 (2011) 1] in which the nitrogen molecule (N-N pair) occupies the vacancy to destroy its original gap-states. We have further observed that the N-doped silicon, which exhibits no softening in its as-grown state, exhibits the softening after the short-time annealing. This suggests that during the annealing the N-N pair is thermally activated to jump off the lattice site leaving the vacancy.