成果報告書詳細
管理番号20110000000436
タイトル*平成22年度中間年報 新エネルギー技術研究開発/革新的太陽光発電技術研究開発(革新型太陽電池国際研究拠点整備事業)/低倍率集光型薄膜フルスペクトル太陽電池の研究開発(広バンドギャップシリコン系薄膜)
公開日2011/7/28
報告書年度2010 - 2010
委託先名シャープ株式会社
プロジェクト番号P07015
部署名新エネルギー部
和文要約和文要約等以下本編抜粋:【研究の概要】(1)広ギャップ材料の開発 本年度は、ガス流量比とプラズマ周波数の最適化によりa-SiC:H膜、a-SiCO膜の膜質改善を行った。i層a-SiCO:Hでは、a-SiC:Hと同等のバンドギャップEg=2.0〔eV〕、光導電率σph>1×10-6〔S/cm〕が得られた。p層a-SiC:Hでは、Eg=1.97〔eV〕、σph>1×10-6〔S/cm〕、Ea=0.4〔eV〕が得られた。 (2)広ギャップセルの開発 (1)で開発したi層、p層を用いたセル試作の結果、Eg=1.93〔eV〕のi層にてJsc=10.0〔mA/cm2〕、Voc=0.946〔V〕、F.F.=0.599、η=5.67〔%〕のa-SiC:Hセルが得られた。また、ショットキー接合を用いることで界面のエネルギー準位を制御し、内蔵電界を印加することでVoc=1.2〔V〕が得られた。
英文要約Title : NEDO Innovative PV Technology,
Thin Film Full Spectrum Solar Cells with Low Concentration Ratios, Wide Band gap Si Based Thin Film
(FY2008-FY2012) FY2010 Annual Report
Thin film silicon-based solar cells have attracted attention as one of photovoltaic cells. In terms of design of the solar cell’s band structure, development of wide band gap material is significant for achievement of stacked solar cells with high efficiency. Photon energy above the energy gap is not effectively utilized since a miss match between the photon energy and the band gap causes photon energy loss in multiple junction cells. Consequently, control of the band structure matching and defect density is required for the efficient utilizing of photon energy and a decrease of recombination in the solar cells with the wide band gap material. Adjustment of band offsets on hetero-junctions is especcially important to achieve a higher efficiency amorphous silicon-based solar cell. It is expected to improve cell’s properties of Voc and FF by suppressing band offsets on the junction. Configuration of conduction band level (Ec), valence band level (Ev) and Fermi level (Ef) based on vacuum level governs the formation of band offset on the junction. There are theoretical approaches to reveal band structure amorphous Si and relationship between the structure and bonding in the amorphous network, however, there is no report concerning directly experimental observation of band structure of amorphous Si-based materials.
In the NEDO project, silicon-based materials are investigated in concepts of controlling of the band structure and defect density. Our group has approached deposition of a-SiC:H as the wide gap material employing plasma-CVD with facile source gases, however, a-SiC:H  deposition has a difficulty in real terms of film quality by means of conventional deposition equipment with a RF (13.56 MHz) power supply because of lower generation efficiency of reactive plasma and plasma damage induced by accelerated plasma. Deposition of a-SiC:H films using very high frequency (VHF) plasma is expected to overcome the difficulty. Moreover, we show the configuration of the band structure on the surface of a-Si thin film deposited by plasma-CVD equipment with a VHF power supply. Ec and Ev were obtained from ionization energy and energy band gap observed by ultraviolet photoemission spectroscopy and optical measurement, respectively. Ef was measured as work function by means of Kelvin probe method. In specipic deposition condition, it is found that Ec and Ev continuously shift to upper level with increasing the frequency while Ef almost keeps constant. It is considered that shifts of energy levels originate from change of bonding characteristics in the a-Si network. This phenomenon is peculiar to amorphous Si-based materials. The results indicate that the upper shift of Ec and Ev are effective in suppressing band offsets on the hetero-junction, especially, in p-side. We show performance of solar cells with controlled band offsets on hetero-junctions and the possibility of higher Voc and FF employing amorphous Si-based materials.
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