By Graham Templeton
There are really only two possible endpoints for human energy production, and they’re both fusion. Either we find a way to create tiny, controlled fusion reactions here on Earth (fusion power) or we find a way to usefully collect a good portion of the energy already being released form the enormous fusion reactor our solar system has built right in (solar power). The nice thing about the solar option is that it can come about incrementally, giving us partial utility while inching ever-closer to the tipping point, when it could provide for the majority of our electrical needs. But what is a solar cell, the centrally important component of solar power, and how does it work?
A solar cell, also called a photovoltaic cell, is defined as any device that can capture some of the energy of a photon of light, and pass that energy on to a device or storage medium in the form of electricity. Not all solar power is photovoltaic in nature, as some solar technologies collect the heat of absorbed photons, rather than their energy, directly. Still, with such a general definition, the term photovoltaics encompasses a wide variety of different technologies.
All of them have one thing in common, however: they use the energy of a photon to excite electrons in the cell’s semi-conducting material from a non-conductive energy level to a conductive one. What makes this complex is that not all photons are created equal. Light arrives as an unhelpful amalgamation of wavelengths and energy levels, and no one semi-conducting material is capable of properly absorbing all of them. This means that to increase the efficiency of capture of solar radiation, we have to make hybrid (“multi-junction”) cells that use more than one absorbing material.