單晶矽太陽電池表面結構之優化

Optimal Surface Nano Structure in Crystalline Silicon Solar Cells

高名璿(Ming-Hsuan Kao)

指導教授 ： 賴芳儀

元智大學/電機通訊學院/光電工程學系/碩士(2011年)

摘要

本實驗利用簡易、低成本的旋轉塗佈(Spin-coating)方式將奈米小球(Polystyrene)以自我組裝方式(Self assembly)在矽基板上形成最密堆積的遮罩，再以乾蝕刻技術製作不同形貌之奈米結構化陣列。本實驗主要目的是以模擬及實做方式，探討蛋形、梯形、錐形奈米結構之抗反射層特性。在模擬方面，首先以Matlab進行等效反射率之計算，接著進行光照射於奈米結構模擬分析，我們採用了RSoft套裝軟體裡的Diffraction Mode來進行模擬。Diffraction Mode是利用廣為大家所熟知的嚴格耦合波分析法(RCWA)技術，可模擬奈米結構之反射率，將之與太陽光頻譜作積分，可得到最佳化的奈米結構。製程方面，我們除了以RIE乾式蝕刻製作不同形貌的次波長結構，並使用缺陷層移除(DRE)溶液將RIE過程中形成的表面缺陷移除。同時，我們量測各種不同製程參數下反射率與生命期，並將量測結果輸入APSYS模擬軟體進行光電特性的計算，以分析其背後之物理機制。根據模擬與製程的結果，我們發現以RIE蝕刻出梯形結構後，若再輔以DRE進行表面缺陷移除，其反射率將會呈現相當幅度的下降，並且生命期會因缺陷的移除而提升，模擬結果顯示其效率達15.51%，與表面平坦矽太陽電池相較，其效率增加了16.53%，同時具有優異的抗反射效果卻又不至於在電性表現上犧牲太大，適合實際應用於太陽能電池元件之上。

關鍵字

太陽電池 ； 單晶矽 ； 奈米結構

並列摘要

Ｗe successfully form self-assemble ,close-packed and monolayer polystyrene nanospheres on the surface of silicon wafers, by employing simpley and cost-effectively spin-coating method. These nanospheres are used as sacrificial etching masks for reactive ion etching (RIE) process to fabricate different profile nano-arrays characterized as broadband antireflective and effective carrier collection structures for enhancing light harvesting of crystalline Si-based solar cells.
Conventional antireflection layers were usually fabricated by depositing a single or multiple layers with restricted thickness and material selection on the silicon solar cells. However, the conventional method exhibited several drawbacks : 1. The stack of layers serve narrow-band antireflective properties. 2. Thermal mismatch and instability of the thin-film stacks have been the major obstacles to achieve broadband antireflection coatings. 3. Selection of materials with proper dielectric constants is difficult.
According to the previous studies, the surface nano-arrays were reported to exhibit better broadband antireflective characteristics than the multiple antireflective layers, it opens up exciting opportunities for photovoltaic devices to further improve performance.
In this project, we intend to demonstrate a high performance, large area Si solar cells by integrateing the antireflective nanostructure,
We utilized rigorous coupled wave analysis (RCWA) method to calculate the reflectance of the nanostructured solar cells and desire to further optimize the light harvesting of the cells. In addition, implementation of the nanostructure will be conducted on silicon-based solar cells to reduce the broadband reflectance. After the RIE process, the samples with trapezoid structure were treated by dipping in HF:HNO3:H2O (2:48:50) solution to remove the damaged layer. This step is called defect removal etching (DRE). Not only the reflectance were reduced but also the lifetime was increased after DRE process. The data of lifetime and reflectance were input to APSYS simulator to calculate the short circuit current, open circuit voltage, and power conversion effeciency. The effeciency of trapezoid structures with DRE treatment achieve 15.51%, which shows an 16.53% compared to flat Si solar cells. We believe the trapezoid structures with DRE treatment are excellent anti-reflectance structures, which are promising candidates to realize the low-cost, high-efficiency solar cells.

並列關鍵字

solar cells ； crystalline silicon ； nano structure

參考文獻

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