體積全像光學於太陽能應用之研究

Abstract

本研究計畫主要在利用體積全像術來設計製作大角度且寬頻的體積全像集光元 件，用於收集並控制太陽光行進方向，以期有效的利用太陽能。此體積全像集光元件 的設計將可達突破性70%的太陽光，而其聚光效果可達10-100 倍，且不需要任何其他 光學元件來進行導光、折光或匯聚光束。 在本計畫中將利用一個前瞻性的概念，90 度體積全像的特性來設計集光元件，故 能將太陽光束繞射到90 度的方向上；再利用柱狀波和平面波來進行記錄體積全像光 柵，將可增加重建光的角度容忍度與波長容忍度，進而使得不同角度入射且寬頻的太 陽光照射於此體積全像時，繞射光將在同一個特定的方向與位置上輸出；此外，利用 重複曝光的技術，我們可以增加角度與波長的容忍度，以期達到全方位角(大於60 度) 與全波段(400nm-700nm)的集光元件。 首先我們將設計並建立全像光學系統來製作此體積全像集光元件，以期達到大角 度與寬頻的集光效果。接著探討體積全像材料的光學特性與製備流程，以期得到最佳 的繞射效率與製程參數。最後，設計並建立大面積的體積集光元件製作與測試系統， 量測其集光效率等各項特性，期能提昇太陽能的集光效率至80%以上。 本計畫之研究工作項目將分三年進行。第一年的計畫將著重在設計體積全像集光 元件，建立全像干涉系統，利用由交通大學光電系許根玉教授與電子物理系林烜輝教 授研究群所研發的感光高分子材料來製作此集光元件，同時量測材料與元件之各項光 學特性，如：繞射效率、感光特性、吸收率、集光角度範圍與波長等等，以期得到大 角度且寬頻的集光元件特性。第二年則進行元件與材料的改進研究，在元件方面，我 們將利用重複曝光與位移多工技術來增加集光元件的入射光角度範圍與收光面積。在 材料方面，我們將探討感光材料的暗反應特性來增加繞射效率。此外，根據前一期計 畫所研發的全像蝕刻系統，我們同時亦將利用三維光子晶體結構的有效控制光傳播之 特性來設計製作新型光子晶體元件來增加太陽能的吸收效率，在光子晶體結構的理論 分析與設計上將由美國壬色列理工學院來進行，我們則利用全像蝕刻系統來製作大面 積光子晶體結構，並進行各項光學特性的量測，期能大幅提昇太陽能模組的集光效率 與吸收效率。最後一年，將根據前兩年的光學實驗量測結果，選用適當的材料來設計 三吋晶圓級全方位角(>60 度)與全波段(400nm - 700nm)的太陽能集光元件，並實際與 太陽能板進行積體化整合，測試太陽能源的轉換效率。

In this program, we propose to use holographic method to create innovative optical devices for solar energy harvesting. This proposed holographic element is capable of achieving (i) an unprecedented solar collection efficiency of >70% and (ii) a solar concentration of 10-100 times without the use of any bulky, external mirrors and, hence, greatly reducing the solar panel cost. The fundamental innovations we proposed are three-folds: (1) the use of volume hologram as an effective mean to diffract light (light-bending) by 900; (2) the combined use of plane-wave and cylindrical wave incident light to enhance the angular-range of solar collection (>600); (3) the use of multiple exposure of laser beams of different color to increase the frequency bandwidth of solar collection, (400nm-700nm). In this program, we will first design and optimize our holographic element to achieve both large-angle and wide-bandwidth solar ray collection. Second, we will synthesis the required volume hologram material, fabricate it into a planar sheet for ease of solar collection and then perform a sequence of holographic recording to create our device. Finally, we will evaluate performance of the fabricated holographic device and especially, its large-angle and wide-wavelength response that would enable greater than 80% solar collection efficiency. The performance period of this program will be three years. In the first year, our focus will be on designing solar-collection elements via volume hologram and establishing holographic interference experimental setup. We will also perform optical characterization of the device such as solar diffraction efficiency, material’s sensitivity to solar ray, angle and frequency response of the device and the overall solar collection efficiency. It is noted that the synthesis of volume hologram material will be based on the state-of-the-art process co-developed by Professors S. H. Lin and Ken Hsu. In the second year, we will continue to improve the performance of our holographic devices and materials. Especially, in the device area, we will employee two new techniques, namely, multiple laser exposure and sequential displacement of the exposure area to increase solar angular collection and concentration factor. In the material area, we will improve material’s sensitivity and also explore the dark effect to increase solar diffraction efficiency. Additionally, we will use a holographic lithography method to produce three-dimensional photonic crystal as an entirely new way to bend light and to enhance solar absorption. As a part of international collaboration with Prof. Shawn-Yu Lin of Rensselaer Polytechnic Institute in the US, the design of photonic crystal will be completed by Prof. Lin’s group and thefabrication be done by my research group at NCTU. In the third year, we will advance our research expertise from the prior 2 years of research experience and attempt to make the high performance solar collection element at wafer scale (3 inch wafer) and with a wide wavelength bandwidth (400nm-700nm). We will also integrate our optical elements with silicon photovoltaic cell to illustrate improvement in solar concentration and solar energy conversion.