An example of a green technology intended to reduce both air pollution and CO2 emissions is the use of photovoltaic cells to generate electricity (actually electrons) from photons emitted by the sun. Given the enormous amount of capital today being invested in solar energy technologies globally from Silicon Valley to the Nation of Singapore, solar energy will unquestionably play a major role in reducing green house gas emissions by supplanting hydrocarbons such as oil, coal and gas as our energy source for many applications. From its start solar energy has been essentially a field of materials science. In the 1970s the first silicon-based photovoltaic (PV) cells were produced. These basic cells were created by doping silicon to form two oppositely charged layers.
All silicon-based photovoltaic solar energy collectors, however, suffer due to their ability to absorb energy only from a relatively narrow range of the sun’s light wave emission. More recently advanced materials have been developed that can either expand this band gap or create multiple band gaps in order to absorb a greater portion of the solar energy spectrum. This has lead to the development of PV cells based onCopper Indium Selenide (CuInSe2) or “CIS” Absorption Layers which can capture energy from portions of the light’s spectrum not collected by silicon-based PV cells. Doping CIS with Gallium increases the band gap even further and as such most PV cells are now based on Copper Indium Gallium Selenide (CuInGaSe2) and are referred to as “CIGS”.