sm sze, physics of semiconductor devices, 2nd ed
TRANSCRIPT
Silicon solar cell – Top view (showing collection grid) and cross section
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Solar Cell: a) pn junction under irradiation; b) equivalent circuit; c) IV characteristics
EFn
EFp
ΙL
Dark current Photo current
c) IV characteristics
Voc
Isc
Max. power point
a) pn junction
b) equivalent circuit
Power conversion efficiency = maximum power / solar power
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Nc
Nv
Nr
EF
G Recombination centers
Minority carrier lifetime, τ
Generation rate =
at high doping level; nn0 = free electron concentration
HJ Hovel, Solar Cells
HJ Hovel, Solar Cells
HJ Hovel, Solar Cells
= generation rate (∝ light intensity at distance x)
Top diffused region
Depletionregion
Base region
Spectral Response Analysis
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Generation rate G(λ) of electron‐hole pairs at distance x from the surface of a semiconductor:
α(λ) = Absorption coefficient at wavelength λF(λ) = Incident photon per unit area per sec per unit bandwidthR(λ) = Reflection at wavelength λ
Top diffused region
Depletionregion
Base region
Recombination losses:
a) Bulk via recombination centersb) Front surface via surface defectsc) Back surface via surface defectsd) Internal junction surfaces
Photon flux
Abs. coeff.
Photon attenuation factorSurface reflection
Spectral Response Analysis
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Spectral Response Analysis – contributions from top (Jp) , depletion(Jdr) and base (Jn) regions
Top diffused region
Depletionregion
Base region
SM Sze, Physics of Semiconductor Devices, 2nd ed.
0.5μm
S = Front surface recombination velocity
GaAs solar cell:
Top diffused region
Depletionregion
Base region
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Loss at this internal surface is much reduced
p-Ga1-xAlxAs / p-GaAs / n-GaAs
p-Ga1-xAlxAs thickness dependence
HJ Hovel, Solar Cells
1.35kW/m2
0.75kW/m2
HJ Hovel, Solar Cells
1.35kW/m2
1.00kW/m2
0.75kW/m2
HJ Hovel, Solar Cells
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Silicon solar cell – Top view (showing collection grid) and cross section
Equivalent circuit with and without series and shunt resisitances:
IL
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Rs
• Rs = series resistance (from bulk, contact)
• Rsh = shunt resistance (from leakage, shorts)
Effect of series and shunt resistances on solar cell performance:
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Back-surface field effect – reduced recombination loss at back contact; increased Isc and Voc
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Texturized surface – increased light trapping and reduced reflection loss
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Vertical junction Si cells – reduced series resistance, but also active area
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Heterojunction solar cells (e.g. CdS/CdTe)
SM Sze, Physics of Semiconductor Devices, 2nd ed.
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Tandem solar cells
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Metal-semiconductor –Schottky barrier solar cells
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Amorphous Silicon Solar Cells
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Concentrator solar cells
SM Sze, Physics of Semiconductor Devices, 2nd ed.
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Solar cells with a spectral-splitting arrangement
SM Sze, Physics of Semiconductor Devices, 2nd ed.
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Luminescent concentrators
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Organic solar cells
SM Sze, Physics of Semiconductor Devices, 2nd ed.
Single‐junction limit
DOE_BES report ‐ http://www.sc.doe.gov/bes/reports/files/SEU_rpt.pdf.