The crystalline silicon heterojunction structure adopted in photovoltaic modules commercialized as Panasonic's HIT has significantly reduced recombination loss, resulting in greater conversion efficiency. The structure of an interdigitated back contact was adopted with our crystalline silicon heterojunction solar cells to reduce optical loss from a front grid electrode, a transparent conducting oxide (TCO) layer, and a-Si:H layers as an approach for exceeding the conversion efficiency of 25%. As a result of the improved short-circuit current (J sc ), we achieved the world's highest efficiency of 25.6% for crystalline silicon-based solar cells under 1-sun illumination (designated area: 143.7 cm 2 ).

An aperture-area conversion efficiency of 20.0% (intrinsic efficiency: 21 .O%) has been achieved for a 1 .Ocm2 CZ n-type single crystalline silicon (c-Si) solar cell, by using the "HIT (Heterojunction with Intrinsic Thinlayer)" structure on both sides of the cell. This is the world's highest value for a c-Si solar cell in which the junction is fabricated at a low temperature of below 200 'C.In this paper, the junction fabrication technologies and features of the HIT structure are reviewed. The stability under light and thermal exposure, and the temperature dependence on performance of a highefficiency HIT solar cell are also reported.

The influence of the Si-H2 bond on light-induced degradation and the thermal recovery of a-Si films and a-Si solar cells were studied. The influence of the Si-H2 bond on light-induced degradation depends on the impurity content in a-Si films, and light-induced degradation can be reduced by decreasing the Si-H2 bond density in a-Si films with impurity content of 1018 cm-3. The activation energy of the thermal recovery process was about 1.0 eV, and it did not depend on the Si-H2 bond density. However, an irreversible phenomenon was observed in film properties and solar cell characteristics with high Si-H2 bond density. It is thought that the structural flexibility of the Si-H2 bond is related to this irreversible phenomenon.

We propose a germanium fin light-emitting diode for a monolithic light source on a Si photonics chip. The germanium fins were fabricated by the oxidation condensation of silicon-germanium sidewalls epitaxially grown on silicon fins. We found that a tensile stress is applied to the pure germanium fins by the difference of the thermal expansion coefficient with that of the surrounding oxide. The electroluminescence spectra were consistent with those expected from direct recombination in germanium with a tensile stress. The strong immunity of germanium fins against high current densities would be favourable to achieve population inversions by electrical pumping.

A high electric field was applied cyclically to poly(vinylidene fluoride) films, during which the simultaneous and time-resolved measurements of the two-dimensional wideangle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and transmission-type Fourier transform infrared (FTIR) spectra were performed using a synchrotron X-ray radiation system. The inversion of the CF 2 dipole moments caused by the alternate change of the electric field vector direction was detected to occur around ±80−100 MV/m as estimated by the electricfield-strength dependence of the IR band intensity. On the other hand, the WAXD peaks were found to show the maximal intensities at 0 and ±250−300 MV/m. In these regions, the 001 reflection of the β form and the 002 reflection of the δ form changed the intensities remarkably and periodically. These experimental data were interpreted, not by the idea of a simple inversion motion of the rigid polar chains (the planar zigzag chains of the form β and the TGTG̅ chains of the α and δ forms) but by the more complicated couplings between the rotation and tilting motions of the chain segments, the cooperative T-G conformational exchanges, and the associated inversion motion of the CF 2 dipoles. The idea of the cooperative chain motions was supported by the density functional theory calculations performed under the external electric field. Different from the remarkable changes of the WAXD and FTIR data, the SAXS patterns did not show the detectable changes in these processes, indicating that the above-mentioned cooperative structural changes should occur in the crystalline regions with the stacked lamellar structure kept unchanged.