成果報告書詳細
管理番号20140000000717
タイトル*平成25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2015/4/24
報告書年度2013 - 2013
委託先名国立大学法人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) FY2013Annual 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), with fine-tuned LSP structures, exhibits a large white-light (400-700 nm) transmittance Haze of around 35% with a relatively low surface roughness as low as 35 nm, that can never be obtained in conventional textured surfaces.

Based upon the experimental observation described above, we have carried out the optical simulation of quantum efficiency spectrum for amorphous silicon single p-i-n junction solar cells formed on ZnO (60-110 nm) / Ag NP / glass substrates. It appears that the simulated quantum efficiency of the device with 60 nm ZnO covering layer is greater by about 5 % in the spectral region 550-650 nm, as compared with that of a reference device fabricated on the standard Asahi VU textured TCO substrate, resulting in 1 % increase in the expected photocurrent. The simulation result is confirmed by preliminary experiments, which convince us of the usefulness of NP LSPs in the optical management technologies in thin-film Si solar cells, not only microcrystalline but also amorphous silicon unit solar cells.

We have, however, comment that the LSP would manifests its potentiality when applied for the back side light-diffusing component, especially in the solar cell system comprised of thin-film Si whose optical band edge spectrum is non-sharp in the infrared light region; that is, microcrystalline silicon. This point grounded on various experimental and theoretical findings suggests us how to effectively utilize the LSPs for higher photovoltaic performances in the thin-film multijunction solar cell systems.
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