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成果報告書詳細
管理番号20160000000711
タイトル*平成27年度中間年報 新エネルギーベンチャー技術革新事業 新エネルギーベンチャー技術革新事業(太陽光発電) ヘテロ接合太陽電池に用いる低温焼結型低抵抗Cu ペーストの開発
公開日2017/6/2
報告書年度2015 - 2015
委託先名株式会社マテリアル・コンセプト 国立大学法人東北大学
プロジェクト番号P10020
部署名イノベーション推進部
和文要約
英文要約Title: New Energy Venture Business Technology Innovation Program / New Energy Venture Business Technology Innovation Program (Solar electric conversion) / Research and development of low temperature firing copper paste having low resistivity for heterojunction solar cells (FY2015 - FY2016) FY2015 Annual report

Hetero junction solar cell (HJ cell) have been attracting considerable attention to archive higher cell efficiency. To compete against solar cells developed in other countries, it is essential for us not only to improve cell efficiency but also to reduce material cost. Cu electrode is a promising material due to its low electrical resistivity, superior resistance to electromigration, and low cost. To replace Ag electrode with Cu electrode, however, firing process must be carried out below 200 oC so as to avoid the degradation of amorphous silicon. In order to make Cu electrode around 200 oC, we employed fine Cu powder, which was expected to be sintered at lower temperature compared to Cu powder used for high temperature paste. A suitable firing process for our low temperature paste was also developed after making low temperature paste suitable for screen printing. Low-temperature-sintering Cu paste was made by mixing fine Cu powder with organic vehicle using a planetary mixer. Viscoelasticity of Cu paste was measured using a rotation viscometer. The prepared Cu paste was printed on a textured 6-inch Si wafer using a screen printing equipment. Width spread and continuity of the printed lines were observed with an optical microscope. After several trials to make low temperature paste, it was found that paste made by only fine Cu powder and vehicle tends to have high viscosity. For example, the viscosity of Cu paste (1) that contained ~20wt% of vehicle was 1770 [Pa・s]. This paste did not have suitable printability because its printed lines showed poor uniformity and poor continuity. We then tried to reduce the viscosity of paste by using different vehicle containing lower content of polymer. This Cu paste (2) had a viscosity of 877 [Pa・s] and this value was within the range to obtain good printed lines as in the case of our high-temperature paste. However, the height of the printed lines was ~8 um and was below our target height (25 um). We thought that these printing problems, poor uniformity, poor continuity, and low line height were attributable to high viscosity and high content of vehicle. To lower the viscosity of paste and the content of vehicle, a small amount of additive (0.1wt.% of Cu weight) was added to the Cu paste (1), and the mixture was well mixed. By using this additive, the viscosity of the paste (1) was reduced from 1770 [Pa・s] to 440 [Pa・s], and the printability of the obtained paste was improved compared to that of the paste (1). We finally found the optimum additive content of 0.2 wt.% with respect to Cu. Although the vehicle content of this paste (~15%) was lower than that of other trial pastes (~20%), the viscosity value of 749 [Pa・s] was within our acceptable range for screen printing. Printability of this paste was good and we could obtain fine printed lines of 40 um width with a good continuity and a small spread.
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