成果報告書詳細
管理番号20110000000652
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)高度秩序構造を有する薄膜多接合太陽電池の研究開発(高度光閉じ込め技術)
公開日2011/8/25
報告書年度2010 - 2010
委託先名国立大学法人大阪大学
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:1. 研究開発の内容及び成果等
2050年までに「変換効率が40%超」かつ「発電コストが汎用電力料金並み(7円/kWh)」の太陽電池を実用化することを目指した研究開発の中で、「革新的太陽光発電技術研究開発」事業では変換効率40%超の実現に向けた技術の基礎・探索研究段階と位置づけて研究開発を実施する。「高度秩序構造を有する薄膜多接合太陽電池の研究開発」(以下、本テーマ)では、40%を超える高効率太陽電池実現のため、最適な複数のバンドギャップを有する高度秩序薄膜材料を新たに設計・創成し、新材料をシリコン系3 接合および化合物系4 接合デバイスに適用し、波長選択型導電層を介して2端子メカニカルスタック太陽電池を形成する。本テーマの一部として、本研究「高度光閉じ込め技術の開発」(以下、本サブテーマ)は、金属ナノ粒子を用いたプラズモン効果を基盤技術として、新規な透明導電層を形成し、テイラーメイドな散乱波長選択性を有する多接合型太陽電池用の高機能透明導電層を開発する。この3カ年では、プラズモン活用による光散乱波長選択制御技術検証に注力し、今年度は、下記の開発内容を実施した。
英文要約Title: Exploring multi-junction thin-film solar cells with highly ordered structures, Development of advanced light management (FY2008-FY2012) FY2010 Annual Report
The light trapping and multi-junction technologies are both indispensable for achieving high efficiencies in thin film silicon based solar cells. It is then required, for example in case of triple junction cells, that the blue portion of solar radiation is trapped in the top cell, the green light in the middle cell, and the red one in the bottom cell, which means that "the front side, back side and inter-cell layers have to be designed to scatter light of specific wavelength regions". Such a wavelength-selective scattering is likely quite difficult in the conventional textured surface approaches, while the localized surface plasmon polariton (LSP) associated with nano-sized metal particles (NP) is expected to offer us a possibility to tune the light scattering wavelength, by controlling the metal particle size, shape and surrounding media conditions. The objective of this work is to examine the availability of the LSP technology for high efficiency thin film solar cells.
We have performed a systematic experimental studies on the tunability of scattering wavelength in the simplest sample structures; i.e. a) Ag NP / ZnO / glass and b) ZnO / Ag NP / ZnO / glass in which Ag NPs are about 200 nm in the mean horizontal diameter and well isolated each other. The transmittance and reflectance spectra of a) and b) samples exhibit twin featured structure owing to ellipsoidal LSP resonant light scattering effects. The shift of the resonant wavelengths found between a) and b) is indicative of "surrounding media effect", which clearly demonstrates the scattering wavelength tunability over a wide spectral region of our interest. The sample b) shows a large white-light transmittance Haze of around 38% with a relatively low surface roughness as low as 20 nm, that can never be obtained in conventional textured surfaces. We have then tried to fabricate c) ZnO / Ag NP / ZnO / Ag / glass samples in order to apply for the backside-diffusing reflector in microcrystalline (mc-) silicon single junction device, and characterize the reflectance Haze and total reflectance spectra. It appears that, if the size of Ag NPs is well designed, the novel LSP substrates c) exhibit quite high reflectance Haze in the wavelength region from 600 nm to 1100 nm, which is most important to enhance the photocurrent of mc-Si solar cells.
Based upon the experimental observation described above, we have attempted to apply the Ag NP LSP for the backside-diffusing reflector in mc-silicon single junction device; the structure was ZnO / p-i-n mc-Si / ZnO / Ag NP / ZnO / Ag / glass. The external quantum efficiency of the device is found greater by about 15 % in the spectral region 600 nm-1000 nm as compared with that of a reference device fabricated on the standard Asahi U textured TCO, resulting in a 8 % improvement in the AM1.5 photocurrent. The result convinces us of the usefulness of NP LSPs in the light management technologies in thin-film solar cells.
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