表面電漿增益矽薄膜太陽能電池之微光學與光電模擬; Optics and Electronics Simulation of Surface Plasmon Enhanced Silicon Thin Film Solar Cells

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/43783

Title:	表面電漿增益矽薄膜太陽能電池之微光學與光電模擬;Optics and Electronics Simulation of Surface Plasmon Enhanced Silicon Thin Film Solar Cells
Authors:	趙建昌;Chien-Chang Chao
Contributors:	光電科學研究所
Keywords:	矽太陽能電池;表面電漿;silicon solar cell;surface plasmon
Date:	2010-07-05
Issue Date:	2010-12-08 14:20:32 (UTC+8)
Publisher:	國立中央大學
Abstract:	薄膜太陽能電池因為有低製造成本以及低製造能量而引起人們的興趣及注意。在各種應用至薄膜太陽能電池的材料當中，矽這種材料有穩定、大量、無毒性以及與半導體製程相容的特性；另外氫化非晶矽薄膜有大面積沉積於各式基板的優勢。在本論文中，我們的研究集中於非晶矽薄膜太陽能電池的光學特性以及光電特性。AMPS-1D (Analysis of Microelectronic and Photonic Structures) 程式可以模擬薄膜太陽能電池的電性表現，而嚴格耦合波理論(Rigorous Coupled-Wave Analysis)以及有限差分時域法(Finite-Difference Time-Domain)分析微奈米結構之波動光學響應。首先由AMPS-1D模擬p-i-n非晶矽薄膜太陽能電池的電性表現，發現當本質層厚度由300nm降為100nm時則其填充因子從0.388升高至0.547，即較薄的太陽能電池能夠有較高的內部量子效率。內部量子效率的上升可以由太陽能電池內建電場的提昇以及光激發的電子電洞對到達電極距離的縮短來解釋。所以為了提高轉換效率，將傾向製作較薄的太陽能電池。然而，較薄的太陽能電池會有吸光能力不足的情況，導致薄膜太陽能電池一般有較低的外部量子效應。為了增加薄膜吸收率，採用介電質光柵結構的遠場散射效應(霧度)，各種ITO光柵週期及深度下的霧度及反射率被計算以及討論。高霧度設計只對於主動層厚度大於400nm時有利；當主動層厚度低於300nm時，抗反射設計反而變得重要。為了增加100nm厚度以下主動層的吸收率，我們使用金屬光柵；這金屬光柵以及原薄膜太陽能電池組成一多層電漿子結構。以嚴格耦合波理論以及有限差分時域法分析此微奈米結構之波動光學性質並且相互比對。藉由角度解析頻譜以及電磁場分佈圖來探討此結構的表面電漿共振效應，可以分辨出兩種不同特性的表面電漿共振模態，即侷域性表面電漿(localized surface plasmon)共振以及表面電漿子(surface plasmon polaritons)共振。這兩個共振模態亦會有耦合的情況，使得原本應該具有狹窄半高寬的表面電漿子共振的頻寬變寬，適合寬廣的太陽光譜。在正向入射光情況下能使電漿子結構太陽能電池有光吸收增強效應28.7%。更進一步分析光吸收的空間分佈，發現在表面電漿共振條件下有部分光子是由金屬材質吸收而不是由主動層吸收，主動層只吸收約50%的入射能量而金屬材質吸收約15%的入射能量，這顯示了一般高估表面電漿共振增強光吸收效率的情況，這額外由金屬吸收的能量並不能貢獻到外部量子效率的部份。當假設非晶矽內的內部量子效率為100%的時候，藉由表面電漿子共振效應可以使短路電流密度(Jsc) 些微增加12.2%。光吸收分佈模擬顯示了在靠近銀光柵角落附近的非晶矽藉由表面電漿共振而獲得額外的光子吸收以及銀光柵的遮蔽效應。我們使用AMPS-1D程式計算出ITO/a-Si:H/Ag太陽能電池的空間內部量子效率。光吸收與空間內部量子效率的空間分佈相關性對於等效的內部量子效率有很大的影響；換句話說，吸收光子的位置也是很重要的。藉由光學以及光電模擬的結合，可以計算出外部量子效率。當產生表面電漿共振的結構遠離主動層的時候，使用表面電漿共振不一定能夠增加主動層的吸收效率。 Thin film solar cells, which require much less energy for fabrication, have recently begun to attract attention. Among the present photovoltaic devices, silicon-based thin film solar cells show the greatest potential, because the material is plentiful, stable, robust and nontoxic. Additionally, silicon-based cells are compatible with existing processes in the well-developed semiconductor fabrication industry. Large area hydrogenated amorphous silicon (a-Si:H) thin film solar cells can be fabricated on various substrates. In this thesis, we focus on the investigations of amorphous silicon thin film solar cells, both in optics and electronics. The analysis of microelectronic and photonic structures (AMPS-1D) program simulates the electrical properties and the rigorous coupled-wave analysis (RCWA) and finite-difference time-domain (FDTD) methods simulate the optical properties. The AMPS-1D program is applied to investigate the thickness effect of an a-Si:H p-i-n thin film solar cell. The filling factor (FF) in J-V curve increases to 0.547 from 0.388 when the thickness of intrinsic layer decreases to 100nm from 300nm. Higher FF implies the higher internal quantum efficiency (IQE) and this improvement can be explained by the increasing of the build-in electric field and the shorting of collection distance of excited carriers. Therefore, for high efficiency, the requirement of thinner solar cells is proposed. However, a thinner solar cell always encounters the light absorption problem leading to lower external quantum efficiency (EQE). The solar cells with dielectric grating with various grating periods and depths are studied for enhancement through its far field scattering effect (Haze effect). The Haze effect only has benefit with an active layer thicker than 400nm. When the active layer is thinner than 300nm, the anti-reflection effect from the dielectric grating becomes important. For enhancing light absorption in active layer thinner than 100nm, a metal grating is applied. The metal grating and original solar cell forms a plasmonic multilayer structure (PMS). The surface plasmon resonances of the PMS are analyzed by the rigorous coupled-wave analysis (RCWA) and finite-difference time-domain (FDTD) methods. The surface plasmon (SP) resonances including the surface plasmon polaritons (SPPs) and the localized surface plasmon (LSP) in the PMS are recognized through angle-resolved spectrums and corresponding field distributions. The coupling between them makes a border absorption band than traditional SPPs on a flat surface; this is benefit for the broad solar spectrum. The absorbed photon numbers can increase 28.7% when the PMS is applied. The spatial distribution and separation of absorptioin in plasmonic solar cells is further studied and we show a usually overestimation of absorption in the active layer. The active layer only absorbs 50% of incident energy while the metallic material absorbs 15%, which can not contribute to the external quantum efficiency (EQE). When the IQE is assumed to be 100% everywhere inside the a-Si layer, the slight enhancement 12.2% of short-circuit current (Jsc) is achieved through the excitation of SPPs resonance. The concentration of energy dissipation around the corners of metal grating and the blocking effect of metal grating are shown. We demonstrate that the spatial-dependent IQE (SDIQE) in ITO/a-Si:H/Ag solar cell through the AMPS-1D program. The correlation between absorption distribution and SDIQE influences a lot in the effective IQE. In other words, the position of absorbing photons is critical. The EQE of plasmonic solar cells is theoretically investigated through the combination of the optics and electronics simulations. The surface plasmon resonances might fail to enhance the light absorption of active layer when the surface plasmon exciter is far from the active layer.
Appears in Collections:	[Graduate Institute of Optics and Photonics] Electronic Thesis & Dissertation

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