Having now defined that a solar cell is a photovoltaic device (see previous post), let me try to explain the bare essentials of what comprises a solar cell. First of all, you need some class of materials from which to build your cell. In one way of looking at things, you can break down all materials into three classes based on their electrical and thermal conductivity (i.e. ability to conduct electricity and/or heat):
Insulators: such as your Styrofoam coffee cup, are great at inhibiting the flow of electricity and heat.
Semiconductors: such as silicon, are pretty resistant to electricity in their most primitive form, but can become great conductors by adding certain impurities, such as boron and phosphorous in the case of silicon.
Conductors: such as the copper wires running through your house, are excellent at passing electricity and, usually, heat.
Owing to some of the magic (i.e. physics) that allows a solar cell to do what it does, it turns out that a semiconductor is best suited for our purpose. Research on semiconductors goes back 100+ years, but modern semiconductor physics and the understanding of how to use them in electrical devices has come from work over the past 50 or 60 years. No, the driving force has not been for solar cells, but primarily for the "brains" of your smarty phones and fancy computers. Yes, the core of your computer, the CPU (central processing unit) along with peripherals, are good old-fashioned chunks of silicon that have been thoroughly ravaged by a variety of processing steps to ultimately enable the ability to process millions upon billions of instructions every second!
As it turns out, semiconductor materials are well "tuned" to collect energy from the sun and convert it to electric power due to a fundamental property that every material has -- the band gap! More on that next time...
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