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Surface Passivation of Crystalline Silicon Solar Cells: A Review
Armin G. Aberle
Progress in Photovoltaics: Research and Application 8,473-487,2000.
2010/8/27 2/5NCTU IEO GPL
Outline
Introduction Fundamental physics Surface passivation method Surface passivation of c-Si solar cells
2010/8/27 3/5NCTU IEO GPL
Introduction
Defects Extrinsic (Processing related) Intrinsic (Si related, unavoidable)
Dangling bond Growth condition Dislocation
2010/8/27 4/5NCTU IEO GPL
Surface type in Si solar cell
Metalized Finger and bus bar Very high surface recombination Avoid recombination loss
Non-metalized Illuminated region Well passivated and good blue response Avoid highly doped
Back electrode high surface recombination Avoid recombination loss
2010/8/27 5/5NCTU IEO GPL
Surface recombination
Shockley-Read-Hall (SRH) theory
Low recombination rate strategy 1. low surface state Nst
2. low carrier concentration ns, ps
Et
Ec
Ev
SurfaceRecombination rate:
2010/8/27 6/5NCTU IEO GPL
Reduction of the surface states
Growth/deposition of a dielectric film SiO2
Al2O3
SiNx
Antireflective coating layer
Chemical methods HF immersion Alcoholic solution
Si solar cell
Dielectric layer(d)
nd
4
2010/8/27 7/5NCTU IEO GPL
Field-effect passivated
High-low junction p+-p n+-n Back surface field (BSF) Front surface field (FSF)
p-n junction MIS Selective emitter HIT(a-Si)
2010/8/27 9/5NCTU IEO GPL
Concept
The fixed charge induced the negative charge on the surface, bending the band diagram.
Al2O3 is suitable to p-type Si substrate.
Al2O3
++++++
------
e-
h+
2010/8/27 10/5NCTU IEO GPL
PERL solar cells
Passivated Emitter and Rear Locally Diffused Solar Cell (24.7%)
2010/8/27 11/5NCTU IEO GPL
Band offset measurement
The Si substrate can passivated by dielectric film and electric field effect method.
The Al2O3 is suitable for p-type Si substrate passivation, and the SiNx is suitable for n-type Si substrate passivation.