利用介電泳力排列奈米銀線陣列應用於矽太陽能電池並提升其光電轉換效率

Abstract

近年來全球二氧化碳含量逐年升高，造成溫室效應和氣候變遷等問題。在能源方面，地球儲存的能源越來越少、石油價格上漲，全球將面臨能源缺乏的危機。因此找出一個可重複使用的綠色能源是目前重要的課題。根據統計結果指出，太陽照射到地球的能量是全球一年所需的一萬倍，所以能利用太陽光能源的太陽能電池受到各界的重視和開發。目前太陽能電池主要可分成無機和有機兩大類，在無機太陽能電池材料方面，目前較廣泛使用的有單晶、多晶及非晶矽，其中以單晶矽太陽能電池光電轉換效率最高，多晶矽、非晶矽及有機太陽能電池的光電轉換效率較低。另外還有三五族的無機太陽能電池，其轉換效率雖略高於單晶矽太陽能電池，但矽的成本比三五族材料便宜很多。 在本篇論文中，我們利用介電泳力來操控奈米銀線，使其在單晶矽太陽能電池的電極之間排列。介電泳力是一種快速、便宜、簡單且能符合傳統製程的方法，且利用此方法排列奈米銀線可使其有方向性地排列在我們想要的位置上。另外，銀是所有金屬材料應用在表面電漿共振上效果最好的，且長條狀的金屬會有兩個吸收波鋒，其兩波鋒之間的吸收光譜是連續分佈的，因此能使太陽能電池效率在大範圍波長間增加。首先，我們用離子佈植使矽基板有PN特性，再用蒸鍍機蒸鍍上下電極，之後沉積一層具有抗反射能力的絕緣層，最後再施加交流電在電極上並滴上含有奈米銀線之溶液。我們可藉由改變奈米銀線之直徑和長度、施加的頻率和交流電壓、溶劑的介電值、電極間距及基板材料來影響排列的結果。 在本實驗中，施加100伏特交流電壓和頻率250千赫茲在50微米電極間距上，並滴下含有直徑50奈米和長度10微米的奈米銀線溶液，可使平行電場排列的奈米銀線與電極平均夾89.17度，標準差為21.98度，更可以使奈米銀線串接至500 µm的電極間距兩端。在光學特性上，有奈米銀線陣列之太陽能電池，可使其反射率降低18.4%；在玻璃上排列奈米銀線，可使其穿透度上升11.2%。在電性表現上，有奈米陣列之單晶矽太陽能電池，其電流最高可提升20%，其填充因子最高可提升57%，其效率最高可提升92%。

During the past few years, global carbon dioxide increased year by year, resulting in the greenhouse effect and climate change issues. Because of the decreasing energy storage of the earth and the soar of oil prices, the world is heading towards a large energy crisis. As a result, it is important to develop some of reusable green energy. The total amount of incident energy from the Sun (32 * 1024 J) upon the surface of the Earth every year is 10,000 times the annually global energy consumption. There are two major categories of solar photovoltaics, inorganic and organic. The most widespread-used inorganic solar photovoltaics are single-crystalline, poly-crystalline and amorphous types, especially single-crystalline silicon photovoltaic cells due to its superior conversion efficiency. In this thesis, dielectrophoresis force is used to align silver nanowires (AgNWs) arrays on the single-crystalline silicon solar cells. Using dielectrophoresis force to align silver nanowires is a quick, simple, and cheap methods and compatible with traditional fabrication. The method can make AgNWs align between electrodes with the same orientation. In addition, silver is the best metal material for SPR enhancement and its wire-shape results in two peaks of absorption. In the experiment process, phosphorous ions are doped in the silicon substrate first to create the n– p junction. AgNWs suspensions are dripped on electrodes while applying alternating voltage after 300 µm silver electrodes and 20 µm thick silicon nitride are deposited on the silicon substrate. We can adjust the parameters of silver nanowires alignment including different gap width of electrodes, material of substrates, voltage, frequency of sinusoidal current, length of AgNWs, diameter of AgNWs, and the permittivity of the medium sequentially to influence the result of alignment. In our study, the optimized result of alignment of AgNWs average angle are 89.17 degree to the electrode edges and 21.98 degree of standard deviation under 100 VPP, 250 kHz on electrode gap of 50 µm by using AgNWs 100nm in diameter and 10 µm in length. In addition, the reflectance is 18.4% lower and the transmittance is 11.2% higher than those without AgNWs ones. The optimized plasmonic solar cells current and fill factor are respectively 20% and 57%larger than those without AgNWs ones. Consequently, the efficiency of the plasmonic solar cell achieves the highest enhancement of 92%.