Surface Passivation of Crystalline Silicon Solar Cells: A Review Armin G. Aberle Progress in Photovoltaics: Research and Application 8,473-487,2000.
Outline • Introduction • Fundamental physics • Surface passivation method • Surface passivation of c-Si solar cells
Introduction • Defects • Extrinsic (Processing related) • Intrinsic (Si related, unavoidable) • Dangling bond • Growth condition • Dislocation
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
Surface recombination • Shockley-Read-Hall (SRH) theory • Low recombination rate strategy • 1. low surface state Nst • 2. low carrier concentration ns, ps Ec Surface Recombination rate: Et Ev
Reduction of the surface states • Growth/deposition of a dielectric film • SiO2 • Al2O3 • SiNx • Antireflective coating layer • Chemical methods • HF immersion • Alcoholic solution Dielectric layer(d) Si solar cell
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)
Concept Al2O3 • The fixed charge induced the negative charge on the surface, bending the band diagram. • Al2O3 is suitable to p-type Si substrate. e- - - - - - - + + + + + + h+
PERL solar cells • Passivated Emitter and Rear Locally Diffused Solar Cell (24.7%)
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.