自然界中有某些材料會因為其結構的不同而導致不同的特性。因此，在此研究中，我們將藉由改變超穎材料(metamaterials)及矽基太陽能電池的結構，來增強其表現及效應。超穎材料為一種次波長(sub-wavlength)的材料，而其整體對應電磁波的響應主要受到其結構的影響而非其本身的材料本質。在過去的十幾年中，超穎材料引起了廣泛的注意，主要是因為它所表現出獨特且前所未有的電磁特性，例如：負折射係數、反司乃爾定律(Snell’s law)、超級透鏡、慢光效應及完美吸收體。儘管如此，超穎材料卻往往受到其對應的入射電磁波的極化方向所限制。舉例來說，表現負磁導率的隙環共振器(split-ring resonator)和表現負電容率的電漿線(plasmonic wires)就必須在側向入射的情況下才能達到，而表現負折射係數的”工”字型金屬線、短金屬線對和兩手超穎材料等，卻只能在正向入射才能達到。因此，在這個研究當中，為了消除上述的限制，我們提出了一個創新的結構，使得超穎材料能夠在不論側向或正向入射的情況下皆能表現出負的磁導率、電容率及折射係數，我們並在微波的頻率下，利用理論計算及實驗結果驗證了此一結果。整體來說，藉由改變傳統超穎材料的形貌，我們成功的設計出一個對應多角度入射的負折射係數超穎材料，這個新的設計可以大大的減輕傳統超穎材料對於入射波極化方向的限制，並將超穎材料推向更廣泛的應用。
除此之外，我們還運用一種成本低廉的濕式蝕刻，Statistic electroless metal deposition (SEMD)，來操控矽的表面形貌，並用來加強矽基太陽能電池的轉換效率，因為現階段來說，各式各樣的光伏原件的性價比相較於石化能源相對太低。為了增加此一性價比，我們必須增加太陽能電池的轉換效率亦或是降低其製作成本。有著優異抗反射能力的矽奈米線(Si nanowires)，將有潛力完成此目標。但沒有額外結構支撐的矽奈米線是很脆弱的，這也可能會阻礙矽奈米線運用到實際的應用上。另外，複雜的矽奈米線製作過程如化學氣相沉積，也會增加其製作成本。幸好，同樣擁有著良好抗反射能力的矽奈米孔洞(Si nanoholes)，相較於矽奈米線有著較佳的機械強度，因此在製作太陽能電池上會是較好的選擇。在此研究裡，我們在室溫下使用一系列的濕式化學方法來製作矽奈米線及矽奈米孔洞並用來製作光伏原件。矽奈米孔洞的太陽能電磁有著優異的抗反射能力，使得其轉換效率高於單面拋光所做成的矽太陽能電池48%。此外，我們也發現矽奈米孔洞所作的太陽能電池比矽奈米線太陽能電池更能夠提供較高的填充因子(fill factor)，這是因為矽奈米孔洞有著較平整的表面。結論是，利用這個低成本的製作方法，我們可望能製作出低成本高效率的矽奈米孔洞太陽能電池。
另外，我們也利用SEMD此一低成本的方法來製作矽微米柵狀太陽能電池，因為若將矽奈米或微米結構應用在太陽能電池上能夠有展現很好的吸收特性和其可分耦光吸收路徑及少數載子傳遞方向的能力。因此，我們在此矽微米柵狀太陽能電池上整合了有著可以將傳統平面電極的反射損失最小化的垂直的側壁電極(vertical sidewall electrodes)，和可以增加載子收集效率的垂直pn介面(vertical multijunction)。利用此一矽微米柵狀太陽能電池，我們成功的將其光伏特性如光電流密度、填充因子和轉換效率，相較於控制組的太陽能電池，分別提升了11.2%、23.7%和52.9%。

A material with varied geometry structures can exhibit distinct material properties. Therefore in this study, we will employ this concept to enhance the performance of metamaterials and Si-based solar cells by manipulating their geometry structures. The concept of metamaterials describes sub-wavelength media whose collective responses arise mainly from their structures rather than their constitutions. In the last decade, metamaterials attract numerous attentions because of its rare and even unprecedented electromagnetic (EM) properties, such as, negative refractive index, inverse Snell’s law, superlensing effect, slowing-light effect and perfect absorber. However, the strong dependence of incident EM wave polarization of the metamaterials will hinder them from the practical applications. For example, split-ring resonators and plasmonic wires exhibit the negative permeability and permittivity respectively only under grazing-angle incidence while the H-shaped metallic wires , short-wire pairs and two-handed metamaterials reveal negative refractive index only under the normal incidence. In this study, to ease the limitation of polarization to the conventional metamaterials, we propose a novel structure to present the negative permittivity and permeability as well as negative refractive index under multi-angle incidence, which is verified theoretically and experimentally in the microwave region. In conclusion, by manipulating the morphology of the conventional metamaterials, we have successfully designed a negative refractive index medium operating at a variety of incident angles to eases the burden of strong anisotropic responses in conventional metamaterials and widely increased the feasibility of practical applications.
Besides, we also exploit a low-cost wet etching method, statistic electroless metal deposition (SEMD) to manipulate the morphology of Si for enhancing the conversion efficiency (CE) of Si-based solar cells (SCs) . This is because currently, the efficiency-to-cost ratio among the diverse photovoltaic techniques remains too low to compete with fossil energy. To boost this ratio, the CE can be improved or the cost of SCs can be lowered. Silicon nanowires (SiNWs), which have excellent antireflective properties, have the potential to facilitate these changes. However, freestanding SiNWs are fragile, and this might hinder the use of SiNWs in practical devices. In addition, complicated procedures, such as chemical vapor deposition, which is often used to fabricate SiNWs, add to the manufacturing cost. Fortunately, silicon nanoholes, which also have excellent antireflective properties, are more robust than SiNWs and are better candidates for use in SCs. In this study, we employ a series of wet and room-temperature processes to fabricate low-cost Si nanoholes (SiNHs) and SiNWs for photovoltaic applications. SiNH-based SCs possess excellent antireflective properties, resulting in an enhanced CE 48% greater than single-side polished Si-based SCs. Moreover, the SiNH-based SCs have an additional advantage over SiNW-based SCs—the flatness of the SiNH surface supports a larger fill factor than SiNWs do. To summarize, such a low-cost fabrication process enables us to fabricate low-cost, high-efficiency SiNH SCs. Furthermore, we also exploit the SEMD method to fabricate Si-micrograting SC (SiMG-SC). This is because that if one applies Si nano- or micro-structured on the SCs, they will exhibit the enhanced optical absorption properties and the ability of decoupling minority carrier diffusion and light absorption paths. Therefore, we monolithically fabricate SiMG-SC with vertical sidewall electrodes and vertical multijunction, which enable to minimize the reflection losses from conventional planar metallic electrodes and to increase minority carrier collection probability, respectively. Based on the SiMG-SC, we consequently intensify the photovoltaic properties of the current density, fill factor, and power conversion efficiency, by 11.2%, 23.7%, and 52.9%, respectively compared to those of the control SCs

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