成果報告書詳細
管理番号20160000000268
タイトル*平成27年度中間年報 高性能・高信頼性太陽光発電の発電コスト低減技術開発 太陽電池セル、モジュールの共通基盤技術開発 CIS太陽電池高性能化技術の研究開発(エピタキシャル成長を利用したCIS太陽電池の高効率化指針の解明)
公開日2016/12/13
報告書年度2015 - 2015
委託先名学校法人東京理科大学
プロジェクト番号P15003
部署名新エネルギー部
和文要約
英文要約Title: Exploring the pathway for high efficiency CIGS solar cells by epitaxial growth technique

Polycrystalline CIGS films deposited on soda-lime glass substrates have been used for state-of-the art high-efficiency solar cells. However, the CIGS films include various types of lattice defects which may act as recombination centers. Therefore, it is difficult to deeply understand the properties of surface/interface and diffusion of impurity in CIGS absorber layers. We thus investigate the epitaxial growth of CIGS thin films for solar cells. For this purpose, Mo back contact layers were first grown onto the sapphire single crystal substrates. The structural properties and epitaxial relations of Mo/sapphire stack layers were investigated by means of RHEED, SEM, and XRD. We developed a two stage sputtering process for the epitaxial growth of Mo thin films. Prior to the sputtering, thermal-cleaning of substrate surface was carried out at 800 C for 90 min. At the first step, 60-100 nm-thick Mo thin films which act as a buffer layer was deposited at relatively low substrate temperatures of 200-600 C onto the 3 cm x 3 cm x 0.5 mm sapphire (0001) single crystal substrates by DC-magnetron sputtering with DC input power of 400 W and Ar gas pressure of 0.5 Pa. Subsequently approximately 400nm-thick Mo film was deposited at the substrate temperature of 800 C. SEM photograph showed that the crystal grains existed for Mo films with no buffer layer even if the substrate temperature increased to 800 C. In contrast, the grains disappeared by introducing the low-temperature buffer layer deposited at 400 C. The RHEED and XRD data revealed that the {111} plane of Mo thin film was epitaxially grown parallel to the sapphire {0001} plane. The optimized thickness and substrate temperature of the low temperature buffer layer were found to be 60nm and 400 C, respectively to achieve high-quality epitaxially-grown Mo thin films. Another merit of epitaxially-grown Mo thin film is its fairly low resistivity as compared to that of polycrystalline Mo layer deposited on soda-lime glass substrates due to reduced grain boundaries. Therefore we can reduce the film thickness of Mo back contact, leading to avoid the peeling-off problem at the Mo/sapphire interface.
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