臺灣博碩士論文加值系統

本研究利用電腦程式進行模擬，探討氧污染對氫化非晶矽(a-Si:H) p-i-n太陽電池的電流-電壓(I-V)特性與量子效率(QE)之影響。氧污染改變a-Si:H的能帶結構，能隙中的高斯缺陷能態密度之峰值隨氧污染而增加，其位置受氧原子具n型摻雜而移動。本質層(i層)的氧污染，導致i層內長波長光生載子的收集效率降低，太陽電池的填充因子明顯降低。
研究使用AFORS-HET軟體模擬具有被氧污染的本質層(i層)a-Si:H p-i-n太陽能電池 之I-V及QE變化並與實驗數據比對。以增加高斯峰值的缺陷密度與峰值位置及氧原子的n型摻雜濃度等參數進行大量模擬，直到模擬的太陽電池的填充因子變得更接近實驗值，以獲得恰當的高斯缺陷能態密度及n型摻雜濃度。這些評估值被用於建立兩個因腔體水氣殘留造成的高與低濃度的氧污染的a-Si:H p-i-n太陽能電池模型。模擬的I-V、QE和△QE值與實驗值非常匹配，借此驗證氧原子汙染模型的正確性。此氧原子汙染模型再用以驗證另外兩個a-Si:H p-i-n太陽能電池。這些太陽能電池的i層具有不同的能隙、厚度和氧污染。模擬結果與實驗結果密切相符，為之前假設的氧污染模型提供了額外的驗證。

To understand the effect of oxygen contamination on the electronic and optical properties of a-Si:H, computer simulation has been used. AFORS-HET (Automata for Simulation of Heterostructures) has been used to simulate a-Si:H p-i-n solar cells, which have i-layers, contaminated by oxygen. The contamination of i-layer effects the photovoltaic process in the solar cell, leading to inefficient collection of carriers in the bulk of the i-layer.
The changes in the electronic structure of a-Si:H due to oxygen contamination have been gathered from literature. It was found that the Gaussian defects in the i-layer are mainly affected by oxygen contamination. The peak defect density increases with oxygen contamination. The Gaussian defects shift closer to the valence band, EV, because of increase in n-type nature. The exact value of peak defect density has been evaluated through numerous simulations, by increasing the peak defect density, until the simulated solar cell’s fill factor becomes closer to the experimental values. These evaluated values have been used to model two solar cells, which have already been experimentally developed. These solar cells have different levels of oxygen contamination. The simulated I-V, QE and QE values closely match the experimental values, and hence, verify the correctness of the physical model for oxygen.
Next, two other solar cells have been simulated. These solar cells have i-layers which have been deposited under different deposition conditions. Hence, the i-layers have different band-gap, thickness and oxygen contamination. These solar cells have been simulated, and the oxygen model, previously developed, has been employed in these two simulations. The simulated results closely match the experimental results, and hence provide additional verification to the proposed model for oxygen contamination.

摘要 i
Abstract ii
Contents iii
LIST OF TABLES vi
LIST OF FIGURES vii
Chapter-1- Introduction 1
Chapter-2- Literature Review 4
2.1. Film Characteristics 4
2.2. Solar Cell characteristics 4
2.2.1. Band Profile 4
2.2.2. Collection Efficiency (Quantum Efficiency) 5
2.2.3. I-V characteristics: 6
2.3. Effect of Oxygen on charged defect density 6
2.4. Effect of Oxygen on dopant-concentration 7
2.5. Effect of Oxygen on band-gap 7
2.6. Effect of characteristic energy of Urbach tail 8
2.7. Solar Cell Simulation: 8
Chapter-3- Electronic Structure of a-Si:H 10
3.1. Gap States 10
3.2. Localized States: 11
3.2.1. Valence Band Tail States: 12
3.2.2. Conduction Band Tail States: 12
3.2.3. Dangling Bonds (Gaussian Defect States): 13
Chapter-4- Physical Modelling of Oxygen atoms 15
4.1. Variation of Gaussian peak position (E) 16
4.2. Oxygen as a dopant 16
4.3. Variation of standard deviation () 17
4.4. Determination of Gaussian parameters 17
4.5. Experimental Results 18
4.6. Variation of Gaussian defect density 19
Chapter- 5- Simulation of 1st Case 21
5.1. Solar Cell – 1 (Negligible Oxygen Concentration) 21
5.1.1. p-layer 21
5.1.2. i-layer 23
5.1.3. n-layer 25
5.1.4. Band-Profile: 28
5.1.5. I-V Characteristics 28
5.2. Solar Cell – 2 (Low Oxygen Concentration) 28
5.2.1. p-layer 29
5.2.2. i-layer 31
5.2.3. n-layer 33
5.2.4. Band-Profile: 35
5.2.5. Comparison of I-V characteristics of simulated and Experimental Values 35
5.3. Solar Cell – 3 (High Oxygen Concentration) 36
5.3.1. p-layer 36
5.3.2. i-layer: 38
5.3.3. n-layer: 40
5.3.4. Band-profile: 42
5.3.5. Comparison of I-V characteristics of Simulated and Experimental values 43
5.4. Comparison of I-V characteristic 43
5.5. Comparison of Quantum Efficiency Characteristic 44
5.6. ΔQE characteristics 45
5.7. Summary of parameters changed in the two cells: 46
Chapter-6- Simulation of 2nd Case 48
6.1. Simulation of 5_1 solar cell 48
6.1.1. p-layer 49
6.1.2. i-layer: 51
6.1.3. n-layer: 53
6.1.4. Band-Profile 55
6.1.5. I-V characteristics 56
6.2. Simulation of 5_30 solar cell: 57
6.2.1. p-layer 57
6.2.2. i-layer: 59
6.2.3. n-layer: 62
6.2.4. Band-Profile 64
6.2.5. I-V characteristics 64
6.3. Comparison of QE between 5_1 and 5_30 solar cells 65
Chapter-7- Conclusion 67
REFERENCES 68

[1] Tai-Chai Kuo, Yeu Long Jiang, “Residual impurities in a process chamber on the characteristics of a-Si:H solar cells”, Solar Energy Materials & Solar Cells 117 (2013) 617-623
[2] Toshihiro Kinoshita, Masao Isomura, Yoshihiro Hishikawa, Shinya Tsuda, “Influence of oxygen and nitrogen in the intrinsic layer of a-Si:H solar cells”, Japan J. Applied Physics, Vol. 35 (1996) pp. 3819-3824, Part 1, No. 7, July 1996
[3] Tatsuo Shimizu, Hideo Kidoh, Akiharu Morimoto, Minoru Kumeda, “Nature of Localized states in hydrogenated Si-based amorphous semiconductor films elucidated from LESR and CPM”, Japan J. Applied Physics, Vol. 28 (1996) pp. 586-592, No. 4, April 1989
[4] M.H.Cohen, H. Fritzsch, S.R. Ovshinsky, "Simple band model for amorphous semiconducting alloys," Phys. Rev. Lett., vol. 22, pp. 1065-1068, May 1969.
[5] N. F. Mott and E. A. Davis, "Electronic processes in non-crystalline materials," Clarendon Press, 1979.
[6] E. A. Davis and N. F. Mott, "Conduction in non-crystalline systems. v. conduction, optical absorption and photoconductivity in amorphous semiconductors," Phil. Mag., vol. 22, pp. 903-922, 1970.
[7] T. Tiedje, J. M. Cebuka, D. L. Morel, and B. Abels, "Evidence for exponential band tail in amorphous silicon hydride," Phys. Rev. Lett., vol. 46, pp. 1425-1428, May 1981.
[8] H. Dersch, J. Stuke, and J. Beichler, "Electron spin resonance of doped glow discharge amorphous silicon," Phys. Status Solidi (B), vol. 105, pp. 26.5-274, 1981.
[9] Y. Kazama, K. Seki, W. Kim, M. K. S. Yamanaka, and K. Takahashi, "High efficiency amorphous silicon solar cells with delta-doped p-layer," Jap. J. Appl. Phys., vol. 28, pp. 1160-1164, July 1989.
[10] Stutzmann, M., “Weak dangling bond coversion in amorphous silicon”Phil. Mag. B 56 (1987) 63.
[11] J. Woerdenweber, T. Merdzhanova, R. Schmitz, A. Muck, U. Zastrow, L. Niessen, A. Gordjin, R. Carius, W. Beyer, H. Stiebig, U. Rau, “Influence of base pressure and atmospheric contaminants on a-Si:H solar cell properties”, Journal of Applied Physics 104 (2008) 094507-1-094507-6
[12] J. Woerdenweber, T. Merdzhanova, A. Gordjin, W. Beyer, H. Stiebig, U. Rau, “Incorporation and critical concentration of oxygen in a-Si:H solar cells”, Solar Energy Materials and Solar Cells 95 (2011) 2811-2815
[13] R. Varache, C. Leendertz, M. E. Gueunier-Farret, J. Haschke, D. Muñoz, and L. Korte. “Investigation of Selective Junctions Using a Newly Developed Tunnel Current Model for Solar Cell Applications.” Solar Energy Materials and Solar Cells 141(2015) 14–23
[14] Liu Jian, Huang Shihua, He Lu, “Simulation of a high-efficiency silicon based heterojunction solar cell”, Journal of Semiconductors, Vol. 36, No. 4
[15] L. Zhao, H.L. Li, C.L. Zhou, H.W. Diao, W.J. Wang, “Optimized resistivity of p-type Si substrate for HIT solar cells with Al back surface field with computer simulation”, Solar Energy 83, (2009), 812-816
[16] L. Zhao, C.L. Zhou, H.L. Li, H.W. Diao, W.J. Wang, “Design optimization of Bifacial HIT solar cells on p-type silicon substrates by simulation”, Solar Energy Materials and Solar Cells 92(2008) 673-681
[17] Jan Wördenweber, “Impact of contamination on hydrogenated amorphous silicon thin films and solar cells”, PhD dissertation, RWTH Aachen University, 2010