techniques for achieving >20% conversion efficiency si-based solar cells qingkai qian department...
TRANSCRIPT
![Page 1: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/1.jpg)
Techniques for achieving >20%conversion efficiency Si-based
solar cells
Qingkai QIAN
Department of Electronic and Computer EngineeringThe Hong Kong University of Science and Technology
December 3, 2014
![Page 2: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/2.jpg)
Outline
I-V curve of solar cellTheoretical limitKeys to improve the efficiency
Maximize light absorptionMinimize recombinationReduce resistance
To transcend the classical limit
![Page 3: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/3.jpg)
Outline
I-V curve of solar cellTheoretical limitKeys to improve the efficiency
Maximize light absorptionMinimize recombinationReduce resistance
To transcend the classical limit
![Page 4: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/4.jpg)
p-n junction: soul of solar cell
Built in electric field separates the photon-generated electron-hole pair.
![Page 5: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/5.jpg)
I-V curve of solar cell
IL : light generated current
![Page 6: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/6.jpg)
Outline
I-V curve of solar cellTheoretical limitKeys to improve the efficiency
Maximize light absorptionMinimize recombinationReduce resistance
To transcend the classical limit
![Page 7: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/7.jpg)
Response to different wavelength
Blue light absorbed at the front surface,Red light absorbed at the back surface,Different absorption site, different efficiency.
![Page 8: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/8.jpg)
Artificial sun standard
International Electrotechnical Commission (IEC)IEC 60904–3: 2008 AM1.5 standard 1000 W/m2 at 25 ℃
¿1
cos (48 °)=1.5
![Page 9: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/9.jpg)
Theoretical output limit
Under AM1.5 solar standard Maximum ISC 46mA/cm2
.
Every photon >1.12eV corresponds to an e-h pair
Maximum VOC Depend on dark current Thermal equilibrium limit 0.85V Auger recombination limit 0.72V
Shockley-Queisser efficiency limit 29.8% Efficiency mainly limited by voltage loss. For example, 3eV photon produces 0.7V voltage.
![Page 10: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/10.jpg)
Outline
I-V curve of solar cellTheoretical limitKeys to improve the efficiency
Maximize light absorptionMinimize recombinationReduce resistance
To transcend the classical limit
![Page 11: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/11.jpg)
Techniques to improve the efficiency
Maximize light absorptionAntireflection layerSurface texturingReduce front metal contact
Minimize recombinationFront and back passivationHeavily doped metal contactHetero-junction with amorphous silicon
Reduce resistance
![Page 12: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/12.jpg)
Light trap: antireflection layer
Minimize reflection for a wavelength of 0.6 µm
Double layer anti-reflection coating (DLARC) ZnS+MgF2 Further reduce reflection too expensive
Bare silicon has a high surface reflection of over 30%.
![Page 13: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/13.jpg)
Light trap: surface texturing• “Roughening" reduces reflection by bouncing back onto the surface.• Anisotropic etching of (100) in KOH
random pyramid texture
random inverted-pyramid textureRear reflector:total internal reflection
![Page 14: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/14.jpg)
Light trap: reduce metal shadowing
EWT: Emitter wrap through solar cell
MWT: Metal wrap through solar cellPossible to move to backside?
Tandem package advantage
![Page 15: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/15.jpg)
Reduce recombination
N-type silicon has a higher surface quality, near p-n junction SiO2 surface passivation Heavily contact region doping
![Page 16: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/16.jpg)
Reduce recombination
• HIT: hetero-junction with intrinsic thin layer• a-Si /Si/ a-Si junction as passivation
![Page 17: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/17.jpg)
Reduce series resistance
Doping of Base (1 Ω·cm)Doping Level of Emitter(100 Ω/ )☐
• Resistance of bulk silicon• Trade off with carrier diffusion length, recombination.
![Page 18: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/18.jpg)
Reduce series resistance
• Resistance of busbar metal• Trade-off with light shadowing.
![Page 19: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/19.jpg)
Effect of these techniques
![Page 20: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/20.jpg)
Records of efficiency
2014 Panasonic HIT® Solar Cell: heterojunction with intrinsic thin layer Highest efficiency of silicon solar cell: 25.6%
![Page 21: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/21.jpg)
Outline
I-V curve of solar cellTheoretical limitKeys to improve the efficiency
Maximize light absorptionMinimize recombinationReduce resistance
To transcend the classical limit
![Page 22: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/22.jpg)
To transcend the classical limit
Tandem solar cell One photontwo e-h pairs two photonone e-h pair
Make the full use of sunlight
![Page 23: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/23.jpg)
Reference• [1] D. M. Chapin, C. S. Fuller, and G. L. Pearson, “A New Silicon p-n Junction Photocell for Converting
Solar Radiation into Electrical Power,” J. Appl. Phys., vol. 25, no. 5, p. 676, 1954.• [2] M. A. Green, A. W. Blakers, J. Shi, E. M. Keller, and S. R. Wenham, “19.1% efficient silicon solar
cell,” Appl. Phys. Lett., vol. 44, no. 12, p. 1163, 1984.• [3] M. A. Green, K. Emery, Y. Hishikawa, W. Warta, and E. D. Dunlop, “Solar cell efficiency tables
(version 44): Solar cell efficiency tables,” Prog. Photovolt. Res. Appl., vol. 22, no. 7, pp. 701–710, Jul. 2014.• [4] M. A. Green, “Limits on the Open-circuit Voltage and Efficiency of Silicon Solar Cells Imposed by
Intrinsic Auger Processes.pdf,” IEEE Trans. Electron Devices, vol. 31, no. 5, pp. 671–678, 1984.• [5] W. Shockley and H. J. Queisser, “Detailed Balance Limit of Efficiency of p-n Junction Solar Cells,” J.
Appl. Phys., vol. 32, no. 3, p. 510, 1961.• [6] T. Tiedje, E. Yablonovitch, G. D. Cody, and B. Brooks, “Limiting Efficiency of Silicon Solar Cells.pdf,”
IEEE Trans. Electron Devices, vol. 31, no. 5, pp. 711–716, 1984.• [7] P. Campbell and M. A. Green, “Light trapping properties of pyramidally textured surfaces,” J. Appl.
Phys., vol. 62, no. 1, p. 243, 1987.• [8] E. Lohmuller, B. Thaidigsmann, M. Pospischil, U. Jager, S. Mack, J. Specht, J. Nekarda, M. Retzlaff,
A. Krieg, F. Clement, A. Wolf, D. Biro, and R. Preu, “20% Efficient Passivated Large-Area Metal Wrap Through Solar Cells on Boron-Doped Cz Silicon,” IEEE Electron Device Lett., vol. 32, no. 12, pp. 1719–1721, Dec. 2011.
• [9] F. Kiefer, C. Ulzhofer, T. Brendemuhl, N.-P. Harder, R. Brendel, V. Mertens, S. Bordihn, C. Peters, and J. W. Muller, “High Efficiency N-Type Emitter-Wrap-Through Silicon Solar Cells,” IEEE J. Photovolt., vol. 1, no. 1, pp. 49–53, Jul. 2011.
• [10] A. Wang, J. Zhao, and M. A. Green, “24% efficient silicon solar cells,” Appl. Phys. Lett., vol. 57, no. 6, p. 602, 1990.
• [11] M. Tanaka, M. Taguchi, T. Matsuyama, T. Sawada, S. Tsuda, S. Nakano, H. Hanafusa, and Y. Kuwano, “Development of New a-Si/c-Si Heterojunction Solar cells: ACJ-HIT (Artificially Consructed Juncion-Heterojunction with Intrinsic Thin-Layer),” Jpn J Appl Phys, vol. 31, pp. 3518–3522, 1992.
![Page 24: Techniques for achieving >20% conversion efficiency Si-based solar cells Qingkai QIAN Department of Electronic and Computer Engineering The Hong Kong University](https://reader036.vdocuments.mx/reader036/viewer/2022062320/56649d225503460f949f83e4/html5/thumbnails/24.jpg)
Thank you!