由於能源缺乏，再生能源很重要，而矽薄膜太陽能電池是再生能源中很重要的一個部份，所以在效率提昇上，有許多研究不斷的被提出來分析矽薄膜特性。其中矽薄膜的吸收係數影響材料的厚度與吸收陽光的頻譜，因此，吸收係數扮演了很重要的角色。由光學上的吸收可以得到很多矽薄膜特性的指標，像是光學能階 (optical bandgap)、矽薄膜膜質的散亂程度Urbach parameter、還有缺陷密度 (Defect density)，缺陷密度的多寡在矽薄膜太陽能電池的效率提升扮演了很重要的角色。矽薄膜在不同波長的吸收大小，在波長小於能階的吸收可歸因於能階內的缺陷所造成的吸收，因此在波長小於能階的吸收特性分析上，顯示不同的物理特性，例如缺陷密度跟Urbach參數又格外的重要，因為缺陷的多寡影響到的是光產生出的電子電洞對效率，缺陷會去捕捉電子電洞對，相對的光生電的效率就會下降。一般而言，簡單的吸收係數可經過光譜儀的量測，再由反射係數與穿透係數來求得吸收係數，但是當吸收小於10-6時，一般的光譜儀便無法量到，需透過其他的儀器Constant Photocurrent Measurement (CPM), Photothermal Deflection Spectroscopy (PDS), and Dual Beam Photoconductivity (DBP)…之類的儀器來量測。本論文的主要架構就是在用CPM去量測弱吸收區的吸收係數，更進一步去得到缺陷密度。不管是PVD還是CVD在製程上都是用氫氣去填補缺陷密度，也就是懸浮鍵（Dangling-bonds），但是氫氣的多寡會影響到膜質的結構，也會影響到矽薄膜的傳導特性（Transport property）；矽氫的鍵結可由紅外線的吸收來求得。非晶矽與微晶矽都是矽薄膜太陽能很重要的成分，由CPM可以得到收係數進而得知微晶矽跟非晶矽不同的光響應，對於製程的優化有很大的幫助。Because lacks of energy, thin film silicon solar cell is an important part to renewable energy in the future, and it still needed to be improved by different methods. Lots of research was devoted to characterize thin film silicon. The absorption coefficient played an important role at thin film silicon solar cell based on Photovoltaics effects and can affect the material thickness and absorption spectrum. From optical absorption, we can get much information to characterize the quality of thin film silicon solar cell, which includes optical bandgap, Urbach parameter(disorder condition) and defect density. The defect density played an important role to optimize the quality of silicon thin film solar cell. The information of optical absorption coefficient not only shows the absorptance condition at different wavelength but also the absorption for the energy lower than bandgap, which indicates gap states information. The absorption in bandgap aroused much attention because absorptance below the band gap attributed to the defect states in the gap. The photo generated electron-hole pairs efficiency is influence by defect densities. The defect would trap electron-hole pairs and decrease photovoltaic effect. Generally speaking, the absorption coefficient can be easily measured by commercial spectroscopy and deconvoluted by transmission and reflection coefficient. However, for absorptance smaller than 10-6, it is not easy to measure absorption coefficient and needed to measure via other equipments such as Constant Photocurrent Measurement (CPM), Photothermal Deflection Spectroscopy (PDS), and Dual Beam Photoconductivity (DBP)…etc.. The main research of this thesis is to measure low absorption coefficient via CPM and calculate defect density. We usually passivate defect density which dominant of dangling bond by introduce hydrogen into chamber at CVD and PVD process. However, more hydrogen will affect the film structure and transport property. The silicon hydrogen bonding can be observed by IR absorption. Above of all, amorphous and microcrystalline silicon thin film are much important in silicon thin film solar cell industry. We can vividly know the different optical response at amorphous and microcrystalline silicon by CPM measurement. And it is great helpful for us to optimize the process condition via the optical properties.
