High-Efficiency HIT Solar Cells for Excellent Power Generating Properties
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1123-P03-01
High-Efficiency HIT Solar Cells for Excellent Power Generating Properties Toshihiro Kinoshita, Daisuke Ide, Yasufumi Tsunomura, Shigeharu Taira, Toshiaki Baba, Yukihiro Yoshimine, Mikio Taguchi, Hiroshi Kanno, Hitoshi Sakata and Eiji Maruyama Advanced Energy Research Center, Sanyo Electric Co., Ltd, Kobe 651-2242, Japan
ABSTRACT In order to achieve the widespread use of HIT (Hetero-junction with Intrinsic Thin-layer) solar cells, it is important to reduce the power generating cost. There are three main approaches for reducing this cost: raising the conversion efficiency of the HIT cell, using a thinner wafer to reduce the wafer cost, and raising the open circuit voltage to obtain a better temperature coefficient. With the first approach, we have achieved the highest conversion efficiency values of 22.3%, confirmed by AIST, in a HIT solar cell. This cell has an open circuit voltage of 0.725 V, a short circuit current density of 38.9 mA/cm2 and a fill factor of 0.791, with a cell size of 100.5 cm2. The second approach is to use thinner Si wafers. The shortage of Si feedstock and the strong requirement of a lower sales price make it necessary for solar cell manufacturers to reduce their production cost. The wafer cost is an especially dominant factor in the production cost. In order to provide low-priced, high-quality solar cells, we are trying to use thinner wafers. We obtained a conversion efficiency of 21.4% (measured by Sanyo) for a HIT solar cell with a thickness of 85µm. Even better, there was absolutely no sagging in our HIT solar cell because of its symmetrical structure. The third approach is to raise the open circuit voltage. We obtained a remarkably higher Voc of 0.739 V with the thinner cell mentioned above because of its low surface recombination velocity. The high Voc results in good temperature properties, which allow it to generate a large amount of electricity at high temperatures. INTRODUCTION To cope with increasing demands for high-quality solar cells from all over the world, we plan to expand the annual production of HIT solar cells from 340 MW in FY 2008 to more than 600 MW in FY 2010. At the same time, we will increase the pace of development to offer technical advantages into our future products. We plan to raise cell conversion efficiency to 23.5% in the laboratory by 2010. We developed a high-efficiency solar cell structure known as the HIT structure, and have been raising its quality. We recently updated the world’s highest conversion efficiency of 22.3 % with a practical-sized solar cell in June 2007 [1]. Also, using high-efficiency HIT cells, we have achieved a record conversion efficiency of 20.6% for an R&D prototype module, which was certified by Advanced Industrial Science and Technology (AIST) [2]. These technologies are being steadily transferred to production. This paper describes the high-efficiency technologies and characteristics of HIT solar cells. HIT SOLAR CELL STRUCTURE The HIT solar cell is primarily characterized by its high conversion efficiency. It is also ap
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