Thames & Kosmos SolarBots, Experiment Manual

Page: 46 / 48

CHECK IT OUT
44 44
Sunlight (Photons)
Electron
p-Silicon
Conductor
Protective layer
n-Silicon
Current
1
4
5
2
Si
Si
Si
Si
P
Si
Si
Si
Si
Electron
Extra electron
Silicon atom
Phosphorous
atom
3
HOW DOES A SOLAR CELL WORK?
The solar cell in this experiment kit consists mostly of a material called silicon, which is a
special semi-metal. Nine out of ten solar cells made worldwide are made of silicon, which
is also the primary material in computer chips.
Electrons — those tiny, negatively charged particles flying around atoms — give rise to
electric current. They are located directly on silicon atoms. Movement of electrons leads to
a change in electrical charge and is known as electric current. To generate electricity, you
need to make the electrons move. That actually happens automatically when light strikes
the silicon. Light particles, called photons, are able to displace electrons from their spots
on the silicon atom (1). But how does the electron know that it’s supposed to move in a
certain direction, such as through the wire into your motor? This is where the structure of
silicon and the design of the solar cell come into play.
Since current is to be generated in a solar cell, the electrical properties of silicon are
important. Silicon is a semiconductor. During the manufacturing process, its electrical
properties can be precisely specified by introducing other elements (such as phosphorous)
into the semi-metal. In a solar cell, two silicon layers that have been altered in different
ways are sandwiched together (2). This results in additional electrons being present (3)
and electrons only being able to move in a certain direction. All of the electrons that are
set in motion under the light end up flowing through on a conductive material (4).
However, since the material is not lacking electrons, it has to be “emptied” from the other
side. A circuit (circular flow) is formed, and current flows through it (5).