成果報告書詳細
管理番号20130000000218
タイトル*平成24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2013/10/31
報告書年度2012 - 2012
委託先名大阪大学大学院基礎工学研究科
プロジェクト番号P07015
部署名新エネルギー部
和文要約
英文要約Title: Exploring multi-junction thin-film solar cells with highly ordered structures, Development of advanced light management (FY2008-FY2014) FY2012 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 35% with a relatively low surface roughness as low as 24 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 (µc-) 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 of 80% on average in the wavelength region from 600nm to 1100 nm, which is most important to enhance the photocurrent of µc-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 µc-Si single junction device; the structure was ZnO / p-i-n µc-Si / ZnO / Ag NP / ZnO / Ag / glass. The external quantum efficiency of the device is found greater by 7%-35 % in the spectral region 600 nm-1100 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, as well as the convesion efficiently. Also challenged was an application of Ag NP LSP for amorphous (a-) silicon solar cells, which is essential to achieve high photovoltaic performance in thin film silicon based multi-junction solar cell system. We have confirmed that test a-Si single junction device provided with specifically tuned Ag NP LSP backside-diffusing reflector exhibits almost the same level of photocurrent as compared with that fabricated on the conventional Asahi VU based substrate. The results convince us of the usefulness of NP LSPs in the light management technologies in thin-film Si solar cells.
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