臺灣博碩士論文加值系統

　　能源危機引起人們對替代性能源的重視，但各種替代性能源都有汙染、破壞生態、因地制宜等缺點。其中，取之不盡用之不竭的潔淨太陽能源是最受到重視的替代性能源之一，利用半導體材料的吸光特性及pn接面產生電流的太陽能電池，自然備受矚目。然而太陽能電池在先天上便受到許多因素的限制，使得光電轉換效率低落。例如主動層的半導體材料有固定的能隙寬度(band gap)，使得光子能量低於能隙寬度的光無法被吸收而激發出電子電洞對以產生電流，而光子能量太強的光雖然被主動層吸收了，但因為吸收的位置在表面，所以產生的電子電洞對再復合(recombination)的機率很高，無法對電流做有效的貢獻；以表面沒有做處理的結晶矽來說，即有30%左右入射光被反射而無法進入主動層加以利用；材料本身吸收光的能力又有所限制。
　　本論文針對HIT(heterojunction with intrinsic thin layer)結構的高效率太陽能電池做表面光柵特性的模擬研究。當非晶矽的厚度足夠厚時，入射的光波會被包夾在空氣和結晶矽層中的非晶矽層而形成平面波導(planar waveguide)，伴隨著週期性粗糙化的表面結構，可透過光捕捉(light trapping)機制，藉由入射光在光柵表面的繞射效應延長光在材料中行走的路徑，提高被吸收的機率；糙化的表面也可使表面對入射光的反射降低，達到抗反射(anti-reflection)的作用，使更多的光有機會進入太陽能電池內；糙化的結構也可降低大角度入射光的反射，使太陽能電池吸光的能力達到寬角度的效果。我們透過調變TCO(transparent conductive oxide)層的光柵週期、蝕刻深度(etching depth)和工作週期(duty cycle)三個變數，來尋找能夠產生較佳短路電流密度(JSC，short circuit current density)的結構以及結構參數對JSC分布的影響，並針對這些JSC較佳的結構來探討磁場能量的分布。最後，由於ITO(tin doped indium oxide)光柵本身對長波長的光有較佳的吸收能力，但被吸收的低能量光無法激發電子電洞對，而是以熱的形式被釋放出，對於太陽能電池所產生的電子電洞對毫無貢獻，光學特性的模擬無法得知結構的電特性，因此我們必須計算出ITO與主動層個別對光的吸收後，忽略掉ITO的吸收後，便可確定主動層在透過表面糙化處理後對光的吸收能力。

Because of the finite deposits of coal, oil and gas in earth, people have to search for a renewable energy. For the reason that solar energy will never run out, solar cell, which can turn light into electricity, is most considerable. The conversion efficiency of solar cell is still low due to the band gap of absorption layer, carrier recombination and surface reflection.
As the thickness of a-Si is enough, the incident light waves can be sandwiched in a-Si layer by air and c-Si layer to result in planar waveguide. Light trapping from surface texturing and planar waveguide can prolong the light path in solar cell and enhance the absorption of thin film solar cell. Textured surface also can reduce the reflection of interface for the usage of anti-reflection coating to enhance the efficiency. In this thesis, we changed the shape of grating to find the best short circuit current density, then plotted the contour map as the function of grating parameters such as duty cycle, period and etching depth to find the optimized grating structure of better short circuit density for HIT( heterojunction with intrinsic thin layer) solar cell. H field distribution had also be taken into account for further study. Considering the absorption of ITO and active layer individually is necessary for the absorption at long wavelength of ITO is useless to generate hole-electron pair. At last we neglected the absorption from ITO and ensure the ability of light absorption of active layer after periodic surface texturing.

摘要 I
Abstract III
目錄 V
表目錄 VII
圖目錄 VII
第一章　序論 1
1-1　前言 1
1-2　研究動機 2
第二章　理論方法與材料特性 7
2-1　模擬方法 7
2-2　HIT太陽能電池模擬結構參數 7
2-3　材料的光學性質 8
2-3.1　結晶矽與非晶矽 8
2-3.2　氧化銦錫 9
第三章　HIT結構參數對短路電流密度之優化 11
3-1　光柵厚度對短路電流密度的影響 11
3-2　表面糙化的增益 13
3-3　非晶矽厚度對短路電流密度的影響 15
3-4　背面反射鏡對短路電流密度的影響 17
第四章　電磁場空間分布及ITO吸收特性的影響 19
4-1　電磁場空間分布 19
4-2　ITO吸收特性的影響 23
第五章　薄型基板HIT太陽能電池之初探 27
5-1　表面無糙化平板結構 27
5-2　薄型基板光柵結構之優化 29
5-3　吸收頻譜與色散曲線 30
5-4　電磁場空間分布 32
第六章　結論 37
參考文獻 39

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