No abstract

The world's highest conversion efficiency levels of 21.8% (Voc: 0.718 V, Isc: 3.852 A, FF: 79.0%, confirmed by AIST) with a practical size of 100.4 cm 2 has been achieved by using the HIT (Hetero-junction with Intrinsic Thin layer) structure. This high efficiency has been mainly realized by the excellent c-Si/a-Si hetero-interface property obtained by our optimized surface cleaning process and high-quality and low-damage a-Si deposition technologies.This excellent c-Si/a-Si hetero-interface of the HIT structure results in a relatively high open circuit voltage (Voc) over 710 mV. Recently, we have succeeded in achieving an outstanding Voc of 730 mV for other efficient HIT solar cells. This result indicates the possibility of further improvement in the conversion efficiency of HIT solar cells. The higher Voc results in not only a higher conversion efficiency but also an improved temperature coefficient, which is another practical advantage for outdoor use.

The highest conversion efficiency to date of 21.5% (confirmed by AIST) with a size of 100.3 cm2 has been achieved in an HIT cell. Because of this high efficiency and the cell's superior temperature characteristics, HIT cells are highly regarded by consumers. Sanyo will increase the production volume of cells and modules to meet the demand both inside and outside of Japan.We have been investigating suitable materials based on Sanyo's technology for fabricating highquality a-Si solar cells to obtain higher build-in potential and control the junction properties, and have been studying how to treat the surface to create a good interface without introducing any damage. We will continue OUT efforts to obtain even higher levels of conversion efficiency by using the high potential that this structure has.

The quality of a-SiGe:H film was improved by considering the effects of substrate temperature and deposition rate on film properties. Accurate measurement of the optical gap and the film composition of Si, Ge and H made it possible to formulate the optical gap using a linear function of bonded H content (CH) and Ge content (CGE). It was found for the first time that, when the optical gap is fixed to a certain value, the optimum compositions of CHAand CGe exist for high-quality a-SiGe:H. Based on these, we obtained the world's highest conversion efficiency of 3.7 % under red light (AM-1.5, 100mW/cm2 through an R65 filter which allows passage of longer wavelength (>650nm) light) for a 1cm2 a-SiGe single-junction cell. Long-term stability of the cell was also improved.

We are developing HIT solar cells with high conversion efficiency, which was achieved the world's highest conversion efficiency of 22.30/0 in a practical size solar cell in July 2007. We have four main approaches to reducing power-generating cost: improve the conversion efficiency, apply the HIT structure to a thin wafer, improve the temperature coefficient, and apply HIT solar cells to a bifacial solar module. Using these approaches, we have achieved the remarkably high conversion efficiency of 21.40/0 due to a high Voc of 0.739 V with an 85-lJm cell, which was measured at SANYO. A thinner Si wafer brings not only high Voc but also generating more output power at high temperature for a better temperature coefficient. We have confirmed that the HIT structure is suitable for use in thinner wafers, allowing us to reduce power-generating cost.