成果報告書詳細
管理番号20160000000222
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/革新的新構造太陽電池の研究開発/超高効率・低コストIIIーV化合物太陽電池モジュールの研究開発(IIIーVセル・モジュール開発・評価)」
公開日2016/12/14
報告書年度2015 - 2015
委託先名国立大学法人宮崎大学
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: Development of high performance and reliable PV modules to reduce levelized cost of energy, Research and Development of innovative new structure solar cells, Research and Development of ultra-high efficiency and low-cost III-V compound semiconductor solar cell modules (III-V cells and modules) (FY2015-FY2017) FY2015 Annual Report

To fabricate III-V semiconductor alloy films on Si substrates, the difference on thermal expansion coefficient between substrates and growth films is critical issue. To avoid the problem, low temperature growth is needed, however low temperature growth generally deteriorates crystal quality. So we applied a pulse laser beam annealing to improve the crystal quality of III-V films without annealing to substrates. GaAs films with film thickness of 400 nm were grown on Si (001) substrates using a molecular beam epitaxy method. A Nd-YAG laser with 1.1 mJ were irradiated to the GaAs films. In the case of 30 seconds of laser irradiation, crystal quality was improved. Usually Germane gas is used as Ge precursor, however, the gas is highly toxic and flammable. So low toxicity and flammable precursors are required. Tertiarybutylgerman is the one of the candidate of such Ge precursor. We found that Ge films could be fabricated at above 430 degrees of growth temperature. The simple silica-based layer, which has functions of anti-reflection and soiling, were coated on the Si PV module. The monthly energy yield of the coated Si PV module showed a 2.52% gain in comparison with that of non-coated Si PV module. For the III-V compound solar cell, optimal film thickness was evaluated by using simulated transmittance, quantum efficiency of a III-V compound solar cell and AM1.5G solar spectrum. Applying the silica-based coating, the output of III-V compound solar cell could be increased. The insertion of a superlattice (SL) structure in the absorbing layer of solar cell is paid attention for increasing the conversion efficiency. Since, the built-in electric field in the SL structure disturbs the miniband formation and increases the carrier recombination, we investigated these effects by using a photoluminescence (PL) spectroscopy. We prepared two kinds of samples with different built-in electric field. The SL structures were both inserted in the i-layer of p-i-n GaAs solar cell samples and the n-layer of n-n GaAs structure samples. We observed one broad peak around 1.30 eV from the PL spectra for all samples and this peak shifted to the low energy side as the barrier width became thinner. This experimental result was explained by the expansion of the miniband width by coupling the electron wave functions of neighbor quantum wells. For n-n GaAs structure sample, the PL intensity drastically decreased with decreasing the barrier width. Supposing that the photo-excited carriers are transported by tunneling though the miniband in the SL structure, this is attributed to the decrease of radiative recombination carrier loss.
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