This document provides an overview of a presentation on solar cells given at Kwame Nkrumah University of Science & Technology in Ghana. The presentation covers the structure and operation of solar cells, materials used in solar panels, solar panel design, applications of solar cells, and concludes with references. Solar cells convert sunlight directly into electricity via the photovoltaic effect and do not require chemical reactions or moving parts like other energy sources. They are made of semiconducting materials arranged in a structure that separates light-generated electron-hole pairs to produce a voltage and current.

1. Kwame Nkrumah University of
Science & Technology, Kumasi, Ghana
A CHEM 255 ( GROUP 1)
PRESENTATION
LECTURER: DR. M. BAAH MENSAH
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CONTENT
 OVERVIEW OF SOLAR CELLS
 STRUCTURE OF SOLAR CELL
 OPERATION
 CRITERIA FOR MATERIALS TO BE USED IN SOLAR PANEL
 SOLAR PANEL DESIGN
 APPLICATIONS OF SOLAR CELL
 CONCLUSION
 REFERENCES

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OVERVIEW OF SOLAR CELL
 A solar cell also known as a photovoltaic cell is an electrical device that
converts the energy of light directly into electricity by photovoltaic effect. It is
a device whose electrical characteristics such as current, voltage or
resistance vary when exposed to light.
 Individual solar cells are the building block of photovoltaic modules known as
solar panels. They are described as photovoltaic irrespective of whether their
source of light is sunlight or artificial light.
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 The overwhelming majority of solar cells are fabricated from
silicon – with increasing efficiency and lowering cost as the
materials range from amorphous to polycrystalline to crystalline
silicon forms. Unlike batteries or fuel cells, solar cells do not
utilize chemical reactions or require fuel to produce electrical
power, and unlike generators, they do not have any moving
parts.
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SOLAR CELL STRUCTURE
 Solar cells can be made from single crystals, crystalline and amorphous
semiconductors.
 For a solar cell one can select a single semiconductor having a junction, usually
referred to as homojunction, or a combination of two materials, with the
junction at the interface referred to as heterojunction. The selected material
needs to match the solar spectrum; i.e., it has to absorb most of the spectrum
for maximizing the short circuit output, therefore it has to have a low band gap.
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 Typical representatives of this class of homojunction semiconductors are Si; several III-V
compounds, most prominently GaAs; and from the class of II-VI compounds CdTe, since it
can be doped p - and n -type, while others cannot. Several ternary compounds are also
used, most prominently CuInSe 2 and similar ternaries. An example for a heterojunction cell
is the CdS/CdTe combination (Meyers and Birkmire, 1995).
 These materials can be employed as single crystals (Si and GaAs), as polycrystals (Si), other
thin-film materials (CdTe and all ternaries), and as amorphous material (a-Si:H). Single
crystals have the advantage of having high crystal quality and a minimum density of
recombination centers; therefore they have a high carrier lifetime that is essential for the
carriers to reach the junction after generation, in order to be separated and to contribute to
the current.
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DIAGRAM SHOWING HOW A PV SYSTEM IS BUILT
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OPERATION
 A solar cell is, in principle, a simple semiconductor device that converts light into electric
energy. The conversion is accomplished by absorbing light and ionizing crystal atoms,
thereby creating free, negatively charged electrons and positively charged ions. If these ions
are created from the basic crystal atoms, then their ionized state can be exchanged readily
to a neighbor from which it can be exchanged to another neighbor and so forth; that is, this
ionized state is mobile; it behaves like an electron, and it is called a hole. It has properties
similar to a free electron except that it has the opposite charge.
 Each photon of the light that has a high enough energy to be absorbed by the crystal's
atoms will set free an electron hole pair. The electron and hole are free to move through
the lattice in a Brownian motion.
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 When they experience an electric field, this will tend to separate the electrons from the holes; the
electrons will drift toward the positive pole (the anode), and the positively charged holes will drift
toward the cathode.
 The resulting potential difference, referred to as an open circuit, can be picked up by an electrometer.
When electrodes are provided at both sides, a current can flow between them. The crystal, when
exposed to sunlight, acts as a battery and becomes a solar cell.
Schematics of a typical solar cell with light falling through an electrode grid onto a semiconductor sheet containing a pn junction that separates
electrons and holes that flow to the respective electrodes and create a current through an external circuit.
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CONT’D
 Such a built-in field is easily created in certain semiconductors that can dissolve a small quantity of
different impurities; can donate a free electron, called a donor; and can also accept an additional
electron, called an acceptor
 When dissolving these impurities (called doping) separately in different parts of the crystal, the region
that contains donors is called the n -type region, the region with acceptors is called the p -type region.
 Between these two regions lies a pn - junction. This region represents the built-in field, since the n -
type region is negatively charged compared to the p -type region.
 The pn -junction can be easily understood in the band model with the conduction band populated by
free electrons and the valence band populated by free holes. Without light, these carriers are created in
thermodynamic equilibrium by donors and acceptors respectively. Mathematically their concentration is
given by the Fermi-function with the determining Fermi level E F , in the n -type region lying essentially
in the middle between the donor level and the lower edge of the conduction band, E c
. N c is the
effective density of states at the lower edge of the conduction band and is on the order of 10 19 cm −3 .
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 A similar equation holds for the density of holes; here the Fermi level lies between the acceptor
level and the upper edge of the valence band.
 The addition of a junction-forming layers, however induces a built-in electric field that produces
the photovoltaic effect. In effect, the electric fields give a collective motion to the electrons that
flow past the electrical contact layers into an external circuit where they can do useful work.
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CRITERIA FOR MATERIALS TO BE
USED IN SOLAR CELL
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 It must have high optical absorption
 It must have high electrical conductivity
 Must have band gap from 1ev to 1.8ev
 The raw material must be available in abundance and the cost must be low

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SOLAR PANEL DESIGN
 Most solar cells are a few square centimeters in area and protected from environment by a thin
coating of glass or transparent plastic. Because a typical 10cm*10cm solar cell generates only
about two watts of electrical power, cells are usually combined in series to boost the voltage or
in parallel to boost the current. Solar panels are slightly less efficient at energy conversion per
surface area than individual cells because of inevitable inactive areas in the assembly and cell-
to-cell variations in performance. The back of each solar cell is equipped with standardized
sockets so that its output can be combined with other solar panels to form a solar array.

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APPLICATIONS OF SOLAR CELLS
 Solar cells are arranged into large groupings called arrays. These arrays function as central electric
power stations, converting sunlight into electrical energy for distribution to industrial, commercial and
residential users.
 Solar cells are installed on rooftops to replace conventional electric supply.
 Solar cells can be used as photodetector, detecting light or other electromagnetic radiation near the
visible range or measuring light intensity
 Because solar cells have no moving parts that could need maintenance or fuels that require
replenishment, they provide power for most space installations from communication and weather
satellites to space stations.
 Solar cells have also been used in consumer products such as electronic toys, calculators, portable
radios. These device utilize artificial light as well as sunlight.

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CONCLUSION
 The photovoltaic process bears certain similarities to photosynthesis, the process by which
the energy in light is converted into chemical energy in plants. Solar cells cannot produce
electricity in the dark, part of the energy they develop under light is stored in many
applications for use when there is no light. One common means of storing electrical energy
is by charging electrochemical storage batteries.
 This sequence of converting light energy into energy of excited electrons and then stored in
chemical energy is similar to the process of photosynthesis.

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REFERENCES
Böer, K. W. (2002). Survey of Semiconductor Physics, Vol. II. New York: John Wiley.
Bube, R. H. (1998). Photovoltaic Materials. London: Imperial College Press.
Chung, B. C; Virshup, G. F.; and Schultz, J. C. (2000). Proceedings of the 21st IEEE Photovolt. Spec. Conf . Kissimee,
FL, p. 179.
Fahrenbruch, A. L., and Bube, R. H. (1983). Fundamentals in Solar Cells. New York: Academic Press.
Gee, J. M.; and Virshup, G. F. (1988). Proceedings of the 20th IEEE Photovol. Spec. Conf . Las Vegas, NV, p. 754.
Green, M. A. (2001). Solar Energy, the State of the Art. London: James & James.
Green, M. A.; Emery, K.; Bucher, K.; King, K. L.; and Igari, S. (2000). "Solar Cell Efficiency Tables." Progress in
Photovoltaics 8: 377.
Meyers, V., and Birkmire, R. W. (1995). Progress in Photovoltaics 3: 393.

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GROUP MEMBERS
NAMES INDEX
ABABIO EMELIA 4240220
ABBEYQUAYE VICENTIA DOIDE 4240320
ABDULMUMIN ABUBAKAR 4240420
ABDULAI GARIBA 4240520
AFUA BOATEMAAABREBRESE 4240620
ABOVOR ELISHA EDEM 4240720
ABUBAKAR BURHAN DEEN 4240820
ABUGRI PAUL AWINSUNGYA 4240920
ACHEAMPONG ASSOR COMFORT 4241220
ACKOM ESTHER ESI OKYEREWAA 4241320
ACQUAH FRANCIS 4241420
NAMES INDEX
ALBERT AMOAKO 4241520
ADJANOR BERLINDA NANA YAA
TEYEMLE
4241620
ADJEI NANA SERWAA WINIFRED 4241720
ADJEI BOAKYE WISDOM DANIEL 4241820
HERBERT ADORFO 4241920
ALICE ADOMAKO 4242020
ADU GYAMFI KELVIN 4242120
WILLIAMS ACHEAMPONG 4241120
ACHEAMPONG GYABENG
EBENEZER
4241020