本論文主要探討在超基板(superstrate)上以兩階段硒化製程形成奈米結構之氧化鋅(或硒化鋅)結合二硒化銅銦鎵異質接面太陽能電池。內容主要分為三個部分，第一個部分是氧化鋅摻鋁的玻璃基板上沉積銅銦金屬先驅物進行兩階段硒化形成二硒化銅銦超基板結構。其中，對於二硒化銅銦所形成的結晶相有深入探討。在第二部分我們應用兩階段硒化來形成硒化鋅包覆氧化鋅的奈米結構鑲嵌在二硒化銅銦吸收層的異質接面太陽能電池。最後，經由改善前面製程堆疊與摻雜鎵到吸收層中來增加奈米結構硒化鋅/二硒化銅銦鎵太陽能電池的轉換效率。
在第一部分我們發現以硒化方式在超基板結構上形成二硒化銅銦的結晶相有別於傳統基板結構。文獻記載(220/204)結晶相有較(112)結晶相還要高的光電響應。因此我們對於該形成之(112)與(220/204)結晶相有深入探討。第一階段以400 oC 硒化，隨著時間的增加二硒化銅銦會趨向於(112)的結晶相，而在第二階段以高於550 oC 與在高的硒蒸氣壓力下二硒化銅銦會趨向於(220/204)的結晶相。探究其原因在於超基板結構因為是以透明氧化導電薄膜當基板，當硒化進行中金屬先驅物的銦會與氧發生作用產生氧化銦。隨著硒化時間增加，氧化銦逐漸會被轉換成(300)結晶相的硒化銦。而(300)結晶相的硒化銦與(220/204)結晶相的二硒化銅銦結構相仿。因此，銦被氧化再轉換成硒化銦的過程幫助了(220/204)結晶相的二硒化銅銦成長。硒化過程會發現銅由於與硒的鍵結能較低，因此銅會偏向表面聚集形成銅偏多的(112)結晶相二硒化銅銦。因此，我們藉由在銅偏多的金屬先驅物沉積後在其上方多沉積一層銦當做金屬先驅物。以此堆疊的先驅物更能成長出(220/204)結晶相的二硒化銅銦。
第二部分我們在超基板結構上製作氧化鋅奈米線隨後以共濺鍍沉積銅銦金屬先驅物。藉由兩階段硒化氧化鋅表面會被轉換成硒化鋅而形成硒化鋅包覆氧化鋅奈米結構鑲嵌於二硒化銅銦的太陽能電池。隨著奈米線的稀疏度與長度不同會影響到光的吸收及轉換效率。在本研究中所製作出來的奈米硒化鋅/二硒化銅銦結構與平面結構太陽能電池相比有較高的光電流產生，而該元件也有1.79%的轉換效率。我們推測該元件效率低的原因可能是硒化過程中殘存的高阻抗氧化鋅造成元件效率不高。
為了增加奈米結構的轉換效率我們將氧化鋅緩衝層厚度降低，在二硒化銅銦吸收層中摻雜鎵來達到較佳的能隙匹配。最後形成奈米結構硒化鋅/二硒化銅銦鎵太陽能電池，而該元件轉換效率提升至3.54 %。

This dissertation investigates the nano-structured n-type ZnO (or ZnSe)/p-type Cu(InGa)Se2-based solar cells which fabricated by two-step selenization with superstrate configuration. The contents are primary divided into three distinct subjects. In the first subject, we investigate the (112) and (220/204)-preferred CuInSe2 films on Al doped ZnO coated glass substrate (superstrate) by two-step selenization. In the second subject, superstrate type nano-structured solar cells with ZnSe/ZnO coaxial nanowires embedded in the CuInSe2 layer are presented. Eventually, nano-structured ZnSe/CuInGaSe2 solar cells with superstrate configuration are performed.
The (112) and (220/204)-preferred CuInSe2 films formed using a two-step selenization process is reported, and the growth mechanism is explained. The selenization temperature, Se vapor pressure, and reactive mechanisms of each selenization step were investigated. The first-step selenization at 400 oC favors CuInSe2 (112) growth as the selenization time increases. For the second-step selenization, a high temperature (≧550 oC) and high Se vapor pressure throughout the process have a strong influence in promoting CuInSe2 (220/204) growth. The oxygen in the self-formed In2O3 layer at the Al:ZnO interface can be replaced by selenium, and transforms to an In2Se3 (300)-preferred film, which favors CuInSe2 (220/204) formation, in a transient and high Se vapor pressure selenization process. A Cu-rich surface, which is the usual case for selenizing precursor and which favors CuInSe2 (112) growth, can be optimized to promote CuInSe2 (220/204) growth by adding a thin In layer onto a slightly Cu-rich Cu/In precursor.
In the second subject, superstrate-type nano-structured solar cells with ZnSe/ZnO coaxial nanowires embedded in the CuInSe2 layer are presented. The Cu/In precursors were deposited on ZnO nanowires/ZnO buffer (100 nm)/ITO/glass substrate in which the ZnO nanowires prepared by chemical-electrically deposition. Complete filling of the CuInSe2 film into the narrow spaces between the ZnO nanowires was realized by growing the nanowires sparsely. The ZnSe/CuInSe2 heterojunction was self-formed by converting a skin (~50 nm) layer of ZnO after the selenization. The influences of the nanowire length and density on light trapping and on cell conversion efficiency have been investigated. A 30% improvement in Jsc and higher efficiency has been achieved by embedding nanowires in the CuInSe2 layer. Conversion efficiency of 1.79 % was obtained from a ZnSe/CuInSe2 heterojunction solar cell fabricated on sparse ZnO nanowires with Voc = 599 mV, Jsc= 11.60 mA/cm2 and 25.71 % fill factor.
In the third part of this dissertation, the optimized film stack and absorber fabrication were investigated. In order to enhance photo generated current collection and reduce carrier loss in the ZnO buffer layer. A thin ZnO buffer (or sacrificing) layer with 50 nm was deposited on ITO substrate. To decrease the conduction band offset ΔEC, the element of Ga was doped into CuInSe2 film. Finally, the nano-structured ZnSe nanowires/CuInGaSe2 solar cells with superstrate configuration are studies. The ZnSe nanowires were transformed from electrochemically deposited ZnO nanowires after selenization. An incomplete selenization of the ZnO buffer layer caused the high series resist and decreased the cell performance. Fully converted ZnSe from ZnO nanowires embedded in CuInGaSe2 enhanced the light trapping at the PN junction and improved carrier collection efficiency, and it generated an open circuit voltage of 449 mV, a current density of 14.43 mA/cm2, a fill factor of 54.7 % and an efficiency of 3.54 %.

Chapter 1
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4. J. Nelson, “The Physics of Solar Cells”, Imperial College Press, World Scientific Publishing Co. Pte. Ltd, Singapore (2003).

Chapter 3
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Chapter 5
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Chapter 6
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Chapter 7
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