An energy conversion efficiency of 25.1% was achieved in heterojunction back contact (HBC) structure Si solar cell utilizing back contact technology and an amorphous silicon thinfilm technology. A new patterning process was established, and it was applied to the fabrication process of HBC cells. In addition, the unique technology of the surface mount technology concept contributed to the superior performance of HBC cell. A shortcircuit current density (J sc ) and an open-circuit voltage (V o c ) were 41.7 mA/cm 2 and 736 mV, respectively. The high J sc as well as the high V o c indicates the strength of HBC structure cell. Besides, a high fill factor of 0.82 was obtained, which shows that HBC structure cell does not have any fundamental critical losses caused from series resistance or shunt resistance. Such high values of I-V parameter means that the patterning process was properly performed.

A spherical Si solar cell with a semi-light-concentration system was successfully fabricated using a spherical Si crystal produced by a dropping method. The dropping method has great potential for low-waste and low-cost fabrication because the Si spheres can be made directly from dropping melted Si without the cutting and polishing processes of Si ingots. The fabricated Si spheres were generally multicrystalline due to the crystal growth through homogeneous crystal nucleation in containerless states. Spherical Si solar cells were fabricated using a Si sphere with a diameter of 1 mm as a solar cell substrate and then mounted on a reflector cup with a hexagonal aperture to complete the semi-light-concentration system. The current–voltage (J–V) measurement of the cell demonstrated an energy conversion efficiency of 10.4%. The key parameters for achieving higher efficiency are discussed with J–V data analysis, and quantum efficiency and laser-beam-induced current measurements.

Spherical Si solar cells are fabricated using polycrystalline Si spheres with a diameter of 1 mm produced by a high-speed dropping method. The distribution and types of electrically active defects in spherical Si solar cells have been directly characterized using electron-beam-induced current (EBIC) and transmission electron microscopy (TEM). Many recombination sink areas in grains and grain boundaries can be directly observed with EBIC in low-efficiency cells. The electrically active defects in grains are stronger recombination sinks than grain boundaries. The electrically active defect areas confirmed using EBIC were selectively etched with a Dash etching solution. TEM images revealed that the area showed a high dislocation density. These results suggest that the dislocations in grains deteriorate the performance of spherical Si solar cells.

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Spherical silicon can be produced directly from melted silicon allowing them to solidify into spherical shape by surface tension; several organizations have carried out trial investigation for fabricate solar cells. Spherical silicon produced by this method are generally polycrystalline and solar cells fabricated from these product are strongly affected by the crystallinity. In this report, an X-ray pole plot analysis of crystal structure of spherical silicon is described. We use pole figure measurement in X-ray diffraction, because distribution and number of the small crystals are directly observable. From (111) pole figure of single crystal as well as polycrystal silicon wafers, we found four poles for the (100) single crystal test sample wafer. In case of the polycrystal, the number of poles is proportional to the number of crystal grains. We have also successfully analyzed the crystallinity of spherical silicon by the pole figure measurement. The (111) pole figure has only four poles in the case of the single crystal spherical silicon. The limitation of sampling position is also discussed.