Key Technologies of Heterojunction Solar Cell and Module Manufacturing
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Key Technologies of Heterojunction Solar Cell and Module Manufacturing
Xiangheng He and Tingkai Li Hunan Gongchuang Photovatic Science and Technology Co. Ltd., No.1 Hongyuan Road, Hengyang, 421005, P.R. China ABSTRACT The a-Si/c-Si Heterojunction Technology (HJT) or Heterojunction with intrinsic thin layer (HIT) solar cell have been fabricated in mass productionˈthe average conversion efficiency of HJT solar cells with 3 bus bar, 5 bus bar and smart wire structures have reached 20%, 21% and 22% respectively. One of the biggest obstructions for HIT module manufacturing is the Cellto-Module (CTM) stringing process where much power loss happened due to high temperature. The higher temperature in stringing process makes passivation quality worse and introduces much more defects. In this article, we present our investigation on CTM string connection methods, especially on which undergo low temperature to avoid thermal micro damage on cell’s functional structure. Several kinds of string connection are elaborated. The discussion will give some directions for further laboratory research and HJT manufacturing. INTRODUCTION The silicon based heterojunction technology (HJT) is very attractive for high efficiency solar cell applications in recent years. Trademarked HIT® solar cell which used heterojunction with intrinsic thin layer technology was invented by SANYO in 1990, and its conversion efficiency achieved 25.6% in April 2014[1]. Using very thin Si rich SiOx:H between a-Si and C-Si can also improve the HJT passivation properties significantly [2]. Despite world records was broken consecutively showing significant progress in solar cell technology, the solar module using HJT cells still cannot realize mass production in the world-wide. One of the obstructions of HJT module manufacturing is the too much power loss in the cell-to-module (CTM) process. Comparing to the power loss of conventional crystalline silicon in CTM process which mainly caused by ribbon series resistance, glass reflection and encapsulation materials’ absorption [3] [4], the HJT CTM power loss is mainly caused by thermal destroy on the intrinsic silicon passivation layer and TCO when the common crystalline silicon CTM stringing method was used. In crystalline silicon CTM production, the solar cell was printed by several Ag bus bars for electricity collection, and used Sn or Sn/Pb alloy coated ribbons as stringing material. Usually, the welding temperature that used to make ribbons contact with cells and Ag bus bars is higher than the deposition temperature of a-Si:H and TCO material. Especially for a-Si:H, the post higher temperature process will make passivation quality worse and introduce more defects. This article introduces three kinds of string solutions: Conductive Film (CF), Electrically Conductive Adhesive (ECA) and low welding point ribbon, which are possible to avoid the damage by post higher temperature process, and make high quality HJT modules in mass production.
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FABRICATION OF HJT SOLAR CELLS The 6 inch HJT solar cell with 3 bus bar,
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