臺灣博碩士論文加值系統

在這研究工作中，我們結合非晶與多晶矽氫薄膜製作不同能隙的吸收層SPA結構的太陽能電池並同時取得完整的光伏特性。針對材料分析方面，我們首先利用低電感天線設計的感應耦合電漿增強化學氣相沉積系統得到未參雜的非晶與多晶矽-氫薄膜,此時非晶矽-氫薄膜的能隙以達到1.75eV而多晶矽氫薄膜亦達到1.285eV,與此同時我們也獲得了82.63%結晶率的多晶矽-氫薄膜。在參雜層的研究方面，多晶N參雜層與非晶P參雜薄膜層分別得到了1.916 Ω-1cm-1與0.552 Ω-1cm-1的結果。而太陽能電池的研究，在完成每一層的厚度控制並利用最佳製程壓力調整的多晶矽氫薄膜層後，效率已經達到1.595%並且在量子效應量測中我們得到短波長與長波長的光譜吸收，再使用退火製程後，效率更提升至1.678%，緊接著我們增加非晶矽P參雜入光層與非晶矽吸收層的能隙，此時效率以增加至3.24%，退火製程後可達到3.56%。我們也針對SPA結構薄膜太陽電池的穩定性做了探討，從太陽能電池完成後並經過了50天，這顆太陽能電池仍可以維持一樣的短路電流與開路電壓。

關鍵字：薄膜太陽能電池、多晶與非晶矽吸收層、全波段光譜吸收。

In this research work, we fabricated SPA solar cell by combining a-Si:H and poly-Si thin films having different band gaps for absorber layers to get the full photovoltaic potential of both. Inductively coupled plasma enhanced chemical vapor deposition system with low inductance antenna design (LIA-ICPCVD) was used to obtain doped and undoped hydrogenated amorphous as well as poly silicon thin films. Amorphous silicon films of 1.75eV band gap and poly-Si films of 1.285eV band gap with a crystalline volume fraction of 82.63% were obtained in this study. Conductivity of n-doped poly-Si and p-doped a-Si:H were 1.916 Ω-1cm-1 and 0.552 Ω-1cm-1respectively. After optimizing the thickness of each layer in this solar structure, we tried to get the required band gap for poly-Si layer by optimizing the process pressure. An efficiency of 1.595% was reached in this case and also QE measurement showed two peaks in shorter as well as in the longer wavelength spectrum. After annealing in hydrogen, efficiency of this cell increased to 1.678%. After replacing the p-doped amorphous Si layer and amorphous absorber layer with larger energy band gap, the efficiency of the cell increased to 3.24% and after annealing it showed an efficiency of 3.56 %.Stability of SPA cell was tested and found that short circuit current and open circuit voltage remained unchanged after 50 days.

Key word: thin film solar cell、poly-Si and a-Si:H absorber layers、full spectral absorption

Contens

Abstract………………………………………………………………….Ⅰ
中文摘要………………………………………………………………..Ⅱ
致謝……………………………………………………………………..Ⅲ Chapter 1. Introduction
1-1. Solar energy…………………………………………...….1

1-2. Development of solar cells...………………………….…3

1-3. Thin film silicon solar cell…………………….…………..7

1-4. Basic Principle of solar cell…………………………...….8

1-4-1 Energy of Photon……………………………………………..10

1-4-2 Band Gap……………………………………………............11

1-4-3 Absorption of Light………………......................................13

1-4-4 Quantum Efficiency..…………….......................................14

1-4-5 Short-Circuit current..…………….....................................16

1-4-6 Open-Circuit Voltage..……………....................................18

1-4-7 Fill factor..…………….......................................................19

1-4-8 Efficiency..……………......................................................19

1-5. Objective…………...………………….……….…….….21

Reference…………...……………...…….………………….……….25

Chapter 2. Experimental Techniques and mechanism of thin film fabrication
2-1. Mechanism of thin film deposition………………….….26

2-1-1 Plasma generation…………………………..……………...26

2-1-2 Gas-phase reaction mechanisms…………………………..29

2-1-3 Secondary reaction…………….…………………………….30

2-1-4 Growth mechanism of silicon thin films on the substrate...32

2-2. Experimental equipment………………..…………....…33

2-2-1 Inductively coupled plasma chemical vapor deposition…………………………………………...……….34

2-2-1-1 Multiple Low-Inductance Antenna……………….....39

2-3. Antenna designs in conventional CCP, conventional ICP and LIA ICP Equipments..........…..………...……42

2-3-1 Conventional CCP antenna design……………...………....43

2-3-2 Conventional ICP antenna design………….……………....44

2-3-3 LIA ICP antenna design…………………….…………..…...44

2-4. Experiment process flow………..………..……….……47

2-4-1 Clean process and experimental precautions…………....49

2-4-2 Extraction of residual gas……………………………..….....51

2-4-3 Pre-passing the process gas…………………..……..….....53

2-4-4 Deposition of Silicon thin film…………………..……..….....54

2-5. Characterization Tools…………………………….……55

2-5-1 Scanning electron microscope…………………...…..…....55

2-5-2 Four point probe…………………………………...…..…....58

2-5-3 Raman Spectroscopy……………………………...…..…....60

2-5-4 Solar Simulators…………………………………...…..…....61

2-5-5 Incident photon conversion efficiency spectrum system....63

Reference…………...……………...…….………………….……….65

Chapter 3. Results and Discussion

3-1. Solar cell results with different layer thickness……….66

3-1-1 Hydrogenated amorphous and poly-Si thin films………...66

3-1-2 Analysis of the SPA cell (C1002) fabricated at first………67

3-1-3 Analysis of the SPA cell C1208 with improved amorphous intrinsic layer quality and reduced polycrystalline n-layer thickness……………………………………………….……..71

3-1-4 Analysis of solar cell C1202 with reduced poly-Si i-layer thickness………………………………………………….….81

3-1-4-1 The mechanism of annealing process……..…….…82

3-2. Solar cell results on Aluminum and ITO substrates: cell C0201…………………………………………………………...87

3-3. Better quality polycrystalline Si thin films……….…….92

3-3-1 polycrystalline layer deposited without argon gas and solar cell C0102 fabricated with this poly-Si layer……………...92

3-3-2 Optimization of process pressure and plasma density…..99

3-3-3 Annealing process of ITO/glass substrates……………....104

3-4. Solar cell fabricated with improved quality of polycrystalline Intrinsic layer: Cell C0301…….….…..117




3-5. Solar cell fabricated with improved quality of polycrystalline Intrinsic layer and with higher band gap amorphous p layer : Cell C0302……………………...123

3-6. Solar cell fabricated with improved quality of poly-Si Intrinsic layer and with higher band gap a-Si:H p-layer and with better conductivity poly-Si n-layer: Cell C0304…….…………………….…………….….…131

3-7. Solar cell fabricated by replacing the p-doped amorphous Si layer and amorphous absorber layer with larger energy band gap : Cell NCTU2……..…137

3-8. Solar cell fabricated with lower polycrystalline intrinsic layer energy band gap : Cell NCTU3…….…............144

3-9. Solar cell fabricated lower polycrystalline intrinsic layer energy band gap with enough thickness: Cell NCTU…………………………………………………...154

3-10. Stability of SPA solar cell…………………………...159

3-10-1 Stability of NCTU-2 Cell………………………………….160

Reference…………...……………...…….………………….……...161

Chapter 4. Conclusion and Future work

4-1. Conclusion………………………….………………………….162

4-2. Future work………………………….………..……………….165

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