What are the successive generations of photovoltaics (PV)?

I have begun this blog as an interdisciplinary exploration of nanomaterials and nanomaterial interactions involved in the synthesis and assembly of Third Generation photovoltaics. So what are the Three Gs (aside from a favorite tequila maker)?

The following are my own interpretations of the three generations of solar cell technologies that have taken root and now have been co-evolving over the past several decades. No doubt, if you have an financial or intellectual investment in one of the three, you will have your own well prepared ideas of what your technology represents. I humbly apologize if I have horribly maligned the status of your research by presenting my interpretations, and invite all to read more about specific technologies at the DOE web site also on the sidebar links.

First Generation: This term refers to the classic p-n junction photovoltaic. Typically, this is made from Silicon (multicrystalline and single crystalline) doped with other elements to make them preferentially positive (p) or negative (n) with respect to electronic charge carriers. However, in the past these devices were made from other materials like Germanium as well.

Second Generation: Thin films of photon-absorbers and layered stacks of thin films. These families of devices are working toward the purest, most efficient capture of light and conversion to electricity. They are elegant and artful, and also delicate and difficult to scale up to industrial levels of production. If the First Gen cells can be viewed as analogous to Microsoft (in that they work, but not optimally), then these varieties are surely the Macintosh-version of solar cells. The materials used in these cells are often designer semiconductor films, and can combine multiple light absorbing materials in a "stack" of films, with each absorbing a slightly different range of light wavelengths than the one below it. While they have been made in the lab and successfully applied in space technologies, they have not gained public attention in the way that Si has. They may prove to be much more efficient in solar energy conversion, but they are much more expensive than a simple silicon wafer.

Third Generation: The wild west! An open territory characterized by monsters of photovoltaic science. This can include dye-sensitized cells, polymer-fullerene cells, ETA cells (for Extremely Thin Absorber, not the radical Basque resistance). Most of the time these are broadly referred to them as "non"-p-n junction photovoltaics, because the old models of p-n semiconductors required a mesoscopic electric field to induce charge carrier "drift", and these devices are a bit more intricate. Some parts of this research are avoided by traditional PV materials scientists and physicists because there is a lot to be learned about the new rules of photovoltaics here that is closer to chemistry.