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Advisor : Walter Varhue PhD. Student: Kofi Adu Asante
School of Engineering (Electrical Engineering) University of Vermont, February 8, 2012  
Demonstrate that a buried Yttria Stabilized Zirconia
(YSZ) insulator shows a significant increase in
photocurrent compared to an epi Si –Si reference
cell.
  Solar cell is a photovoltaic device designed to
convert sunlight into electrical power .   Success in PV technology requires advances in
efficiency and cost reduction  
 
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Light breaks silicon bonds and creates “free”
electrons and holes “missing electrons”
Holes are positive charges
Built-in field separates electrons and holes
n-type
P+
eP+
B-
P+
B-
B-
E-field
h
p-type
Solution: Light trapping
ThinFilm PV
  One way to improve the efficiency of solar cells is to
make light bounce around inside them, increasing the
chances that it will be absorbed.
> Requirement: media with a different refractive index
  Thin film reduces the amount of materials used in PV
cells, which cuts cell
  Randomly roughened surface increase the path
length enhancement by 50 times. Crystalline SiGe and Si films are grown directly on a
previously deposited heteroepitaxial layer of YSZ.
YSZ Properties:
Refractive index = 1.8-2.1 Bandgap= 5.8eV
Acts as a perfect Lambertian
Surface
High temperature epi growth (above 1000oC) by
CVD has been employed in the industry
  Because high temperature can not be used in many
cases. New solutions are needed.
  Plasma enhances precursor gas decomposition and
reactions
  Keeps wafers at lower temperatures compared to
thermal CVD processes
 
 
 
 
Low temperature growth of a epitaxial Si film on Si
substrate with an insulator layer
The insulator layer, yttria-stabilized zirconia (YSZ),
is deposited via a reactive sputtering process in an
electron cyclotron resonance (ECR) reactor.
YSZ is relatively small lattice mismatch of about
5% with Si. Epitaxial SiGe and Si films were grown directly on a
previously deposited heteroepitaxial layer of YSZ.
YSZ Properties:
Refractive index = 1.8-2.1 Bandgap= 5.8eV
Acts as a perfect Lambertian
Surface
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PV properties 1.  Open circuit Voltage
2.  Short circuit voltage
3.  Fill factor 4.  Efficiency