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In order to reduce the po wer-generating cost of silicon solar cells, it is necessary to achieve a high conversion efficiency using a thinner crystalline silicon (c-Si) substrate. The HIT (Heterojunction with Intrinsic Thin-layer) solar cell is an amorphous silicon (a-Si) / c-Si heterojunction solar cell that exhibits the potential to make this possible. Our recent R&D activities have achieved the world's highest conversion efficiency of 23.0% with a practical sized (100.4 cm 2 ) HIT solar cell, by improving the quality of the surface passivation, reducing the optical absorption loss and reducing the resistance loss. We have also developed a HIT solar cell with a thickness of only 98 µm, which has a very high conversion efficiency of 22.8%. This value is comparable to that of the conventional HIT solar cell, which has a thickness of more than 200 µm. Moreover, we have fabricated HIT solar cells using thinner c-Si substrates (96 to 58 µm), and found that the Voc increased with decreases in the substrate thickness, and reached an extremely high value of 0.745 V with a thickness of only 58 µm. This indicates that the surface recombination velocity of the HIT structure is extremely low due to the excellent passivation of the c-Si surface.

In order to reduce the power-generating cost of silicon solar cells, it is necessary to achieve a high conversion efficiency using a thinner crystalline silicon (c-Si) substrate. The HIT solar cell is an amorphous silicon (a-Si) /crystalline silicon (c-Si) heterojunction solar cell that makes it possible to realize excellent surface passivation and hence high open circuit voltage (V oc ). In addition, its symmetrical structure and a low-temperature fabrication process that is under 200C provide advantages in reducing thermal and mechanical stresses within the device so that it can easily be applied to thinner solar cells. We fabricated HIT solar cells using thin wafers from 58-98 μm, and achieved a 22.8% conversion efficiency with a HIT solar cell using a 98-μm-thick wafer, and an excellent V oc value of 0.747 V with a HIT solar cell using a 58-μm-thick wafer.

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