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We achieved the highest conversion efficiency of 9.5% in a large area amorphous silicon (a-Si) solar cell (40 cm×30 cm) for the first time in the world. It was achieved by employing surface technologies, such as, the optical confinement structure, the high quality a-Si fabrication technique, and high quality a-Si germanium technology. Using the a-Si technology HIT solar cell that is a hybrid of a-Si and c-Si was also developed. The conversion efficiency of a module using HIT solar cells is 15.2% that is the highest for the products. In addition to high conversion efficiency the HIT structure solar cell has an improved temperature dependence compared to conventional c-Si cells.

A new solar cell roofing tile combining a building material (a glass Japanes-style roof tile) and an amorphous silicon (a-Si) solar cell has been developed. It was made possible by developing new technologies for uniformly fabricating a-Si film on complex curved surfaces such as Japanese tiles and for patterning integrated-type solar cells on large-area curved surfaces. The roofing tiles were installed on a model house and are presently undergoing exposure tests. Their performance as solar cells and as building materials has been satisfactory over the past 2 years.

Applications of thin-film solar cells, especially a-Si, started in the 1980s mainly in the field of electrical devices. By utilizing the features of thin-film solar cells, unique applications such as larger electrical power sources have been developed. Three kinds of applications are introduced in this chapter. The first one is the see-through a-Si solar cell, the second is the flexible a-Si solar cell, and the final one is the building integrated PV (BIPV) module. In the future, thin-film solar cells are expected to play an important role for the widespread use of solar cells from the field of electrical devices to the field of electrical generating use on a global scale.