Genetic algorithms for high-precision reconstructions of three-dimensional topographies using stereo fractographs

A software is developed which enables reconstruction of the three-dimensional (3D) shape of fracture surfaces without human assistance. It is based upon computer image processing and pattern recognition techniques by using a stereo-pair of scanning electron micrographs. The processing consists of two subprocesses: searching the matching points between two images; and computation of heights using the relative shift of the matching points. By using the previously developed system, some mismatches were inevitable in the search process, in particular, for low-contrast SEM images, e.g. striations, intergranular facets, etc. In order to improve the accuracy of the search, a genetic algorithm (GA) was implemented into the developed system. By using the GA method, the 3D shapes of a wide variety of fracture surfaces including cleavage failures, intergranular cracking, dimples and fatigue striations, were successfully reconstructed with sufficient accuracy. The searching processes by the GA method and the previously developed two-step algorithm of coarse and close searching were compared. These proved that the GA method has both the advantage of accuracy in the searching process and a short run-time. A detailed 3D shape, of more than a 120 × 120 reconstructed point-sized shape, was thus obtained with sufficient accuracy and with a relatively short run-time.     

A high efficiency thin film silicon solar cell and module

A photoelectric conversion efficiency of over 10% has been achieved in thin-film microcrystalline silicon solar cells which consist of a 2 μm thick layer of polycrystalline silicon. It was found that an adequate current can be extracted even from a thin film due to the very effective light trapping effect of silicon with a low absorption coefficient. As a result, this technology may eventually lead to the development of low-cost solar cells. Also, an initial aperture efficiency as high as 13.5% has been achieved with a large area (91 cm × 45 cm) tandem solar cell module of microcrystalline silicon and amorphous silicon (thin film Si hybrid solar cell). An even greater initial efficiency of 14.7% has been achieved in devices with a small size (area of 1 cm²), and further increases of efficiency can be expected.     

A thin‐film silicon solar cell and module

We have developed a new light‐trapping scheme for a thin‐film Si stacked module (Si HYBRID PULS module), where a (a‐Si:H/transparent interlayer/microcrystalline Si) thin‐film was integrated into a large‐area solar cell module. An initial aperture efficiency of 13·1% has been achieved for a 910 × 455 mm Si HYBRID PLUS module, which was independently confirmed by AIST. This is the first report of the independently confirmed efficiency of a large‐area thin‐film Si module with an interlayer. The 19% increase of short‐circuit current of this module was obtained by the introduction of a transparent interlayer that caused internal light‐trapping. A mini‐module was shown to exhibit a stabilized efficiency of 12%. Outdoor performance of a Si HYBRID (a‐Si:H / micro‐crystalline Si stacked) solar cell module has been investigated for over 4 years with two different kinds of module (top and bottom cell limited, respectively). The HYBRID modules limited by the top cell have exhibited a more efficient performance than the modules limited by the bottom cell, in natural sunlight at noon. Copyright © 2005 John Wiley & Sons, Ltd.     

Large area thin film Si module

An initial efficiency of 14.1% (J_sc=13.6 mA/cm², V_oc=1.392 V, FF=74.3%) has been achieved for a-Si/transparent interlayer/poly Si solar cell (total area of 1 cm²). Both a-Si and crystalline Si films were fabricated by plasma chemical deposition at low temperature. The short circuit current was enhanced by the introduction of a transparent intermediate layer. An initial aperture efficiency of 11.7% has been achieved for 910×455 mm² a-Si/poly Si integrated solar cell submodule, where the laser-scribing techniques were applied for series interconnections. The results of our first run of 266 submodules in our pilot plant showed the average efficiency of 11.2%, which is applicable for mass production.