chapter 8 thin film solar cells july 12, 2015
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TRANSCRIPT
Chapter 8 Thin Film Solar Cells
April 21, 2023
Requirements for suitable materials
Doping and charge transport are more difficult for a-Si.
Amorphous silicon
Absorption
Doping
Low doping efficiency means
• P is much less than ND.
• Femi level moves toward the defect level in the center of band gap and majority carrier activation energy is large.
• The built-in potential is less.
• In addition, recombination centers for minority carriers increases.
More explanations
• Vbi = [EFn(wn) – EFp(wp)]/q,
• Vbi = φn –φp = -(Ei – EF)/q – [-(Ei – EF)]/q
= kTln[NAND/ni2]/q
Pp0 = pn0exp[qVbi/kT]
Voc could not increase by increasing ND or N
A. kTEEc
FceNn /)(
Transport
The small diffusion length of a-Si is attributed to the small mobility of the carriers. Mobility of c-Si is 0.5 m2V-1s-1 for electron with low doping.
Stability
C; absorption by defects of dangling bond.
B: absorption by Urbach tail due to variation of bond length and angle.
the i-region thickness to around 0.5 μm.
Amorphous Silicon Solar Cell Design
The p-i-n solar cell device physics
Fabrication of a-Si solar Cells
Light induced degradation:
The Staebler Wronski effect is the most important barrier to widespread use of a-Si solar cells. Light-induced degradation is stronger
Strategies to improve a-Si cell performance
where EF is above EC or below EV.