The basics on materials

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...

Photovoltaics...what!?

For the first post, let's start at the top. I'm an electrical engineering PhD student at Purdue University. Electrical engineering itself covers a vast domain, so if we whittle it down a bit further, you could say I study/do research on solid-state devices. Big help, huh? Let's break that down:

solid-state: composed entirely of a solid material
device: a charge-carrying component that functions, in some way, on its own

Thus, solid-state devices represent a large field of electronic components ranging from complex microprocessors (the brains of your computer) to a simple junction diode (an electronic switch).You may also hear the term microelectronics used simultaneously with solid-state devices, where "micro" refers to a device or circuit built on the scale of a micron (= 10^-6 meter). However, the two are really mutually exclusive, since microelectronics may include other types of devices, and solid-state devices are not limited to the micron scale (see: nanotechnology).

Drilling down further, you have the vast field of photovoltaics (PV), a type of solid-state device. Similar to the photoelectric effect defined by Einstein, the photovoltaic phenomena was discovered in 1839 by Alexandre-Edmond Becquerel. A photovoltaic device harnesses the energy in a light source and converts this energy to electrical current by way of a voltage between two terminals.

photo: light, radiant source
voltaic: voltage-producing (which, in turn produces a current when connected to a load)

If you haven't put it together yet, a solar cell is a PV device. It's just a specialized type of PV device that uses sunlight to produce the electric power (power is a term of measurement that is equal to the voltage times the current, in units of Watts). Certainly, you could take a solar cell inside your house and drop a lamp over it, call it a "lamp cell" and still produce power, but the power produced by your cell will never be greater than the power used by your lamp...ever.

PV is one of several ways to collect energy from the sun. So, if you hear something in the media about new plans for solar energy production, they may not be talking about solar cells. You will also see solar thermal, solar hot water heaters, and perhaps thermoelectrics.

Hopefully, this gives you a broad perspective of what I work on -- solar cells! More details to come...