臺灣博碩士論文加值系統

低能隙之氫化微晶矽可有效吸收長波長之光譜，非常適合應用於高效率薄膜串疊型太陽電池中作為底層之子電池。在優化微晶矽薄膜太陽電池中，提升長波長的光利用率 (700-1100 nm) 是重要課題之一。因此，本研究使用優化的背反射結構以提升光利用率進而提升微晶矽薄膜太陽電池之轉換效率。研究中的微晶矽薄膜太陽電池是由27.12 MHz的電漿輔助化學氣相沉積系統所製作。首先，優化高電導之n型微晶矽作為摻雜層以進一步提升載子收集能力;另一方面，優化低折射率之n型微晶矽氧作為背反射層以提升電池背接觸面的反射量。研究中，使用最佳化之n型微晶矽與微晶矽氧作為摻雜與背反射層，並與不同的背反射層做比較，發現n型微晶矽氧比起透明導電氧化層用作為太陽電池背反射層具有更好的短路電流與開路電壓，非常有潛力能取而代之，並同時簡化了電池的製程。實驗成果於單接面微晶矽薄膜太陽電池達到之最佳轉換效率為7.2%，開路電壓為0.50 V、短路電流為20.83 mA/cm2以及填充因子為69.9%;雙接面太陽電池最佳轉換效率為10.3%，開路電壓、短路電流以及填充因子分別為1.35 V、10.62 mA/cm2及72.0%。

The hydrogenated microcrystalline silicon (μc-Si:H) thin-film solar cell is the promising candidate for employing as the bottom cell in the multi-junction device due to its higher absorption coefficient in the long-wavelength range (700-1100 nm). A well-operated back reflecting layer (BRL) in the μc-Si:H solar cell is quite essential to assist in reflecting unabsorbed photons back into the absorbing layer, resulting in increasing the photon absorption and improving the cell performance. To improve the μc-Si:H cell performance, the n-type hydrogenated microcrystalline silicon (μc-Si:H(n)) and microcrystalline silicon oxide (μc-SiOx:H(n)) materials were characterized and optimized for the employments as the doped layer and the BRL, respectively. In this thesis, the μc-Si:H solar cells were prepared by the 27.12 MHz radio-frequency plasma-enhanced chemical vapor deposition (PECVD) system. By adjusting the deposition condition of RF power, H2-to-SiH4 flow ratio and pressure, the highly conductive μc-Si:H(n) materials were obtained and employed as the doped layer to establish the built-in electric field and facilitate the carrier collection. Moreover, the lower refractive index μc-SiOx:H(n) materials were employed as BRLs to improve the reflection and raise the absorption of absorbers in μc-Si:H solar cells. To meet the requirements of employing as BRLs, the adjustments of μc-SiOx:H(n) in the H2-to-SiH4 flow ratio and CO2-to-SiH4 flow ratio were executed.
The applications of different BRLs in μc-Si:H solar cells were investigated. By using μc-SiOx:H(n) as an alternative to ITO, the higher external quantum efficiency (EQE) and improved cell performance were achieved. Furthermore, the fabrication processes can be simplified by the in-situ processes of μc-SiOx:H(n) compared to the ex-situ sputtering steps of ITO. The optimal cell efficiency 7.2% in μc-Si:H single-junction solar cells was obtained, with the VOC of 0.50 V, JSC of 20.83 mA/cm2 and FF of 69.9%. In the a-Si:H/μc-Si:H tandem cells, the best cell efficiency 10.3% was achieved, with the VOC of 1.35 V, JSC of 10.62 mA/cm2 and FF of 72.0%.

中文摘要 I
Abstract II
Acknowledgements IV
Content VI
Table Captions IX
Figure Captions XI
Chapter 1 INTRODUCTION 1
1.1 Problems of Global Energy Supply and Possible Solutions 1
1.2 Introduction to Photovoltaic (PV) Technology 4
1.2.1 Current Development of PV Technology 4
1.2.2 Thin-Film Solar Cell Technology 6
1.2.3 Silicon-Based Thin-Film Solar Cells 7
1.3 Motivations 10
Chapter 2 LITURATURE REVIEW 11
2.1 Operation Principle of Solar Cells 11
2.2 Carrier Collection Mechanism with p-n or p-i-n Junction 13
2.3 Introduction to c-Si and a-Si:H 15
2.4 Stabler-Wronski Effect - Light Induced Degradation 16
2.5 Introduction to µc-Si:H 17
2.6 Process of Doping 19
2.7 Plasma-Enhanced Chemical Vapor Deposition System 20
2.8 µc-Si:H Solar Cell 21
2.9 Back Reflector and Back Reflecting Layer 22
2.10 N-Type Hydrogenated Microcrystalline Silicon Oxide 22
Chapter 3 EXPERIMENT DETAILS 24
3.1 RF-PECVD System 24
3.2 AM 1.5 Light Source 25
3.3 Analytical Tools 26
3.3.1 Raman Spectroscopy 26
3.3.2 Measurement of Elemental Composition 28
3.3.3 Definition of Optical Bandgap (E04) 29
3.3.4 Measurement of Dark Conductivity 29
3.3.5 X-Ray Diffraction (XRD) 31
3.3.6 Spectroscopic Ellipsometry 31
3.3.7 Fourier Transform Infra-Red (FTIR) Spectroscopy 32
3.3.8 Measurement of J-V Characteristic and Cell Efficiency 33
3.3.9 Measurement of External Quantum Efficiency 34
Chapter 4 RESULTS AND DISCUSSION 36
4.1 Preparation and Characterization of Highly Conductive μc-Si:H(n) as Doped Layers in μc-Si:H Solar Cells 36
4.1.1 Effect of RF Power on μc-Si:H(n) Film Properties 36
4.1.2 Effect of H2-to-SiH4 Flow Ratio and Pressure on μc-Si:H(n) Film Properties 43
4.1.3 Employment of Highly Conductive μc-Si:H(n) as Doped Layers in μc-Si:H Cells 47
4.2 Preparation and Characterization of Lower Refractive Index μc-SiOx:H(n) as Back Reflecting Layers (BRL) in μc-Si:H Solar Cells 49
4.2.1 Effect of CO2-to-SiH4 Flow Ratio on μc-SiOx:H(n) Film Properties 49
4.2.2 Effect of H2-to-SiH4 Flow Ratio on μc-SiOx:H(n) Film Properties 51
4.2.3 Employment of Lower Refractive Index μc-SiOx:H(n) as BRLs in μc-Si:H Solar Cells 59
4.2.4 Comparison of μc-Si:H Solar Cells with Lower Refractive Index μc-SiOx:H(n) as Back Reflecting Layers 65
4.3 Application of Improved μc-Si:H Solar Cells with Double N-Layer Structures and Wider Bandgap μc-SiOx:H(p) as P-Layers in a-Si:H/μc-Si:H Tandem Solar Cells 73
4.3.1 Employment of μc-Si:H(n)/μc-SiOx:H(n) Double N-Layer Structures in a-Si:H/μc-Si:H Tandem Solar Cells 73
4.3.2 μc-Si:H Solar Cells Employing Wider Bandgap μc-SiOx:H(p) as P-Layers for Reducing Optical Absorption Losses 77
Chapter 5 CONCLUSION 84
Chapter 6 FUTURE WORK 86
Chapter 7 REFERENCES 87

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