臺灣博碩士論文加值系統

In this thesis, the physics of CIGS and micromorph solar cells are investigated by numerical simulation. At first, simulation models are established and compared with experiment results. Then some issues of high efficiency thin film solar cell are discussed.
Among several thin film solar cells, CIGS solar cell has a record efficiency ~20%, but the progress has largely been driven by empirical optimization rather than by in-depth understanding of appropriate physical models. Therefore, some critical issues for achieving high conversion efficiency are discussed including(1) optimum single band gap of CIGS solar cell and the effects of CBO between CdS/CIGS layers; (2) effects of Ga-grading on CIGS solar cell; (3) effects of junction properties on CIGS solar cell. These simulation results give some insights to achieving high cell efficiency.
Micromorph solar cell has a stack tandem structure and consists of an amorphous silicon top cell and a microcrystalline silicon bottom cell. The interconnection between top and bottom cells is via Esaki tunnel diode. The simulated J-V curve has an S-shape and 33.4 A/cm2 maximum tunnel current Jpeak, which is much greater than photo-generated current Jphoto to prevent distorted J-V curve. The optimal thickness of absorber layer is also discussed and indicates the efficiency of micromorph solar cell is sensitive to current matching. Furthermore, the EQE responses of subcells under different voltage bias are studied by simulation. The different behaviors of top and bottom cell are discussed and referred to difference of optical generation distribution. Finally, surface texture is considered into simulation model and optimizes the texture size. The optimal texture size gives a 2% efficiency improvement than planar structure.

Contents
List of Tables………………………………………………………...VIII
List of Figures………………………………………………………....IX

Chapter 1 Introduction………………………………………………...1
1.1 Introduction……………………………………………………………………….1
1.2 Motivation ………………………………………………………………………..2

Chapter 2 CIGS Solar Cell Simulation ………………………………3
2.1 Introduction………………………………………………………………………3
2.2 Conventional CIGS solar cell simulation………………………………………...4
2.2.1 Basic simulation structure and parameters…………………………………4
2.2.2 Simulation results…………………………………………………………..7
2.3 Uniform distribution of Ga content in CIGS solar cell………………………….11
2.3.1 Effect of Ga content on physical properties of CuIn(1-x)Ga(x)Se2 absorber layer………………………………………………………………………..11
2.3.2 Simulation structure and model…………………………………...............17
2.3.3 Simulation result with ideal CdS/CIGS interface recombination (R=0)...........................................................................................................17
2.3.4 Effect of conduction band offset of CdS/CIGS interface…………………19
2.3.5 Simulation result with large CdS/CIGS interface recombination (R=105cm/s)………………………………………………………………..23
2.4 Ga-grading absorber layer in CIGS solar cell…………………………………...25
2.4.1 Ga-grading CIGS absorber layer………………………………………….25
2.4.2 Simulation structure and model…………………………………………...26
2.4.3 Simulation results………………………………………………………….27
2.4.4 Comparison of simulation results………………………………………….31
2.5 Effects of junction properties on CIGS solar cell………………………………..32
2.5.1 Possible junction properties of CIGS solar cell……………………………32
2.5.2 Simulation structure and model……………………………………………34
2.5.3 Simulation results………………………………………………………….36
2.5.4 Comparison of simulation results………………………………………….40
2.6 Summary................................................................................................................42
References....................................................................................................................43

Chapter 3 Micromorph Solar Cell Simulation……………………...45
3.1 Introduction……………………………………………………………………...45
3.2 Material Characteristics of amorphous silicon and microcrystalline silicon……46
3.2.1 Amorphous silicon………………………………………………………….46
3.2.2 Microcrystalline silicon……………………………………………………..50
3.3 Physics of p-i-n solar cell………………………………………………………..53
3.4 Amorphous Si / microcrystalline Si tandem solar cell simulation………………55
3.4.1 Concepts of a-Si/ u-Si tandem solar cell……………………………………55
3.4.2 Basic simulation structure of a-Si/ u-Si tandem solar cell………………….56
3.4.3 Tunnel diode of a-Si/ u-Si tandem solar cell………………………………..58
3.4.4 Basic simulation result of a-Si/ u-Si tandem solar cell……………………..63
3.5 Optimization of absorber layer thickness of micromorph solar cell…………….66
3.6 Summary………………………………………………………………………...71
References...................................................................................................................72



Chapter 4 EQE and texture simulation of micromorph solar cell….74
4.1 Introduction……………………………………………………………………....74
4.2 EQE simulation of micromorph solar cell…………………………………….....75
4.2.1 EQE of tandem solar cell…………………………………………………....75
4.2.2 Simulation model and result………………………………………………...77
4.2.3 EQE of subcells at different voltage bias……………………………………81
4.3 Texture simulation of micromorph solar cell…………………………………….95
4.3.1 Surface texture of micromorph solar cell……………………………………95
4.3.2 Simulation structure and model……………………………………………..96
4.3.3 Simulation results……………………………………………………………97
4.4 Summary………………………………………………………………………..100
Reference……………………………………………………………………………101
Chapter 5 Summary and Future work……………………………..101
5.1 Summary………………………………………………………………………..101
5.2 Future Work………………………………………………………………….....104

Ch2 References

[1] K. Ramanathan, M. A. Contreras, C. L. Perkins. Properties of 19.2% efficiency ZnO/CdS/CuInGaSe2 thin film solar cell, Prog. Photovoltaics 11 (2003) 225-230.
[2] Markus Gloeckler. NUMERICAL SIMULATIONS OF Cu(In,Ga)Se2 SOLAR CELLS. PhD Thesis, Colorado State University, Fort Collins, Colorado (2005)
[3] Terada et al., Thin Solid Films vol.480-481 pp.183-187,(2005) Kong et al., Proceeding of MRS (2005)
[4] D. Schmid, M. Ruckh, and H. W. Schock, Sol. Energy Mat. Sol. Cells 41-42, 281(1996)
[5] P. D. Paulson, R. W. Birkmire, and W. N. Shafarman. “Optical characterization of CuIn1ÀxGaxSe2 alloy thin films by spectroscopic ellipsometry” JOURNAL OF APPLIED PHYSICS VOLUME 94, NUMBER 2 15 JULY 2003
[6] Miquel A, K. Ramanathan, J. AbuShama. Diode Characteristics in State of the Art ZnO/CdS/CuIn1-xGaxSe2 Solar cells. Prog. Photovolt: Res Appl. 2005; 13:209-216
[7] Richard H. Bube “ Photovoltaic Materials” Imperial College Press (1997).
44
[8] Su-Huai Wei, S. B. Zhang, and Alex Zuger “Effects of Ga addition to CuInSe2 on its electronic, structural, and defect properties”, Appl. Phys. Lett., Vol. 72, No. 24, 15 June 1998
[9] D.J. Schroeder, J.L. Herberholz, A.A. Rockett, in: Proceedings of the 11th International Conference on Ternary and Multinary Compounds, 1999, pp. 749–752.
[10] Shockley W, Queisser H. Detailed balance limit of efficiency of p-n junction solar cell. Journal of Applied Physics 1961; 32(3): 510-519.
[11] T. Nakada and A. Kunioka: Appl. Phys. Lett. Vol.74, No.17(1999)2444-2446
[12] M.A. Contreras, B. Egaas, K. Ramanathan, J. Hiltner, A. Swartz-lander, F. Hansoon, R. Noufi, Prog. Photovoltaics: Res. Appl. 7(1999) 311
[13] Y. Yan, K.M. Jones, J. Abushama, M. Young, S. Asher,M.M. Al-Jassim, R. Noufi, Appl. Phys. Lett. 81 (2002) 1008–111
[14] D. Schmid, M. Ruckh, F. Grunwald, H.W. Schock, J. Appl. Phys. 73 (1993) 2902–2909.
[15] F.S.Hasoon,Y.Yan,H.Althani,K.M.Jones,H.R.Moutinho, J. Alleman, M.M. Al-Jassim, R. Noufi, Thin Solid Films 387 (2001) 1–5.

Ch3 References

[1] Richard H. Bube “ Photovoltaic Materials” Imperial College Press (1997).
[2] S.R. Dhariwal*, S. Rajvanshi, “Theory of amorphous silicon solar cell (a):
numerical analysis”, Solar Energy Materials & Solar Cells 79 (2003)
199–213
[3] S.R. Dhariwal*, S. Rajvanshi, “Theory of amorphous silicon solar cell (b): a
five layer analytical model”, Solar Energy Materials & Solar Cells 79 (2003)
215–233
[4] N. Hernandez-Como, A. Morales-Acevedo, Solar Energy Materials & Solar Cells 94 (2010) 62-67
[5] U. Dutta and P. Chatterjee, “The open circuit voltage in amorphous silicon
p-i-n solar cells and its relationship to material, device and dark diode
parameters”, JOURNAL OF APPLIED PHYSICS VOLUME 96, NUMBER
415 AUGUST 2004
[6] A.Fantoni rt al., Mathematics and Computers in Simulation 49 (1999) 381-401
[7] T. Brammer, H. Stiebig, J. Appl. Phys., Vol. 94, No. 2, 15 July 2003
[8] H. Takakura*, Y. Hamakawa, “Device simulation and modeling of
microcrystalline silicon solar cells”, Solar Energy Materials & Solar Cells 74
(2002) 479–487
[9] Street R, Hydrogenated Amorphous Silicon, Cambridge University Press, Cambridge (1991).
[10] L. Esaki, “ New phenomenon in narrow germanium p-n junction,” Phys. Rev., vol. 109, no. 2, pp. 603-604, Jan. 1958.
[11] Guter W, Bett AW,” I–V CHARACTERIZATION OF TUNNEL DIODES AND MULTIJUNCTION SOLAR CELLS,” IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 53, NO. 9, SEPTEMBER 2006
[12] Hurkx GAM, Klaassen DBM, Knuvers MPG. A new recombination model for device simulation including tunnelling. IEEE Transactions on Electron Devices 1992; 39: 331–338.

Ch4 Reference

[1] A. Luque, S. Hegedus, “Handbook of Photovoltaic Science and Engineering.” 2003
[2] Hitoshi SAI, Homare FUJII, Koji ARAFUNE, Yoshio OHSHITA. Jpn. J. Appl. Phys., Vol. 46, No. 6A (2007)