Download Photovoltaic and dye-sensitized solar cells

Energy topic 8
Photovoltaic and dye-sensitized solar
cells
Semiconductors
Semiconductors
• A solid substance that has a conductivity
between that of an insulator and that of most
metals, either due to the addition of an
impurity or because of temperature effects.
Devices made of semiconductors, notably
silicon, are essential components of most
electronic circuits.
Semiconductors versus metals
Low Temperature
-Metals conduct electricity due to delocalised electrons
-Semiconductors don’t really work at low temperatures
High Temperatures
-Metals still have same amount of delocalised electrons;
however ions moving more so resistance increases which
affects the overall conductivity
-More electrons released from the material which
increases its conductivity
Silicon
• Sp3 hybridised
• No conductivity at absolute zero
• As the temperature increases the electrons get freed and the
conductivity increases
• Its an intrinsic semiconductor as the energy comes from
within
• The number of positive holes equals the number of free
electrons
Doping
N type’s electrical conductivity is due to negative
carriers. (still uncharged)
P type’s electrical conductivity is due to positive
carriers (still uncharged)
Silicon
Diodes
pn-junction Diodes
• Here p-type and n-type semiconductors are joined
together.
• The principal characteristic of a pn-junction diode is that it
allows current to flow easily in one direction but hardly at
all in the other direction.
We call these situations forward bias and reverse bias,
respectively.
• This means that it can convert alternating current into
direct current
Youtube video
• https://www.youtube.com/watch?v=ar7xDMR
4P_U
Questions
Answers
Photovoltic cell
• Light causes electrons to
gain energy
• Electron leaves and an
ion is left behind
• Normally when the
electron looses the
energy (as heat) it will
rejoin and form a
neutral atom
• This does not happen in
a photovoltaic cell
Photovoltic cell
• Due to the electric
field caused by the p-n
junction current is
produced
• The electron will pass
around the whole
circuit before rejoining
the atom
Summary
• Make a list of the advantages and
disadvantages of photovoltaic cells
Dye-sensitized solar cells
A dye-sensitized solar cell (DSSC, DSC, DYSC or
Grätzel cell) is a low-cost solar cell belonging to
the group of thin film solar cells. It is based on a
semiconductor formed between a photosensitized anode and an electrolyte, a
photoelectrochemical system.
Anode – porous layer of titanium dioxide
Cathode – Transition metal wire
The dye
The dye absorbs light due to the conjugated
system in the molecule
Questions
Solution
Summary
• What are the advantages and disadvantages
of dye-sensitized solar cells