Solar energy science

The amount of sunlight that reaches the surface of the Earth each hour is approximately as much today's society uses in an entire year [1], but in order to harness this power, we need to find materials that are both more efficient at converting light into energy and cheap to produce.

The solar cells prevalent today are typically made of semiconductor materials, such as silicon.  These photovoltaic cells are expensive - in both energy and cost - to produce.  For example, a typical commercially-available solar cell requires two years to generate the energy that was required to make it! 

A promising development for solar cells which are cheap and energy efficient to manufacture is to use organic "plastic" materials.  These materials, termed organic because they are made mostly of carbon, are typically polymers - thousands copies of the same molecule linked end-to-end.  These materials can be made at reasonable temperatures in the form of sheets, films, and coatings. The problem is that scientists don't know which molecules will efficiently absorb light and convert it into energy.

An efficient solar cell needs to be able to perform several different steps.  First, the light must be absorbed by the molecules.  For this to happen the incoming light must match or be greater than the energy levels of the molecule.  After the molecule is excited by light, the negative charge (electron) and positive charge (hole) must be separated.  Only then can the charges move to the terminals of the cell to be connected to an electrical circuit.  All of these steps are affected by the structure of the molecules themselves and how they pack together in the material.

This is where the Clean Energy Project comes in!  We can study three of the major aspects involved in converting sunlight to energy using the World Community Grid: molecular packing structure, absorption of sunlight, and transfer of electrons and holes. 

[1] N. S. Lewis, G. Crabtree, Eds., Basic Research Needs for Solar Energy Utilization (U.S.
Department of Energy, http://www.sc.doe.gov/bes/reports/files/SEU_rpt.pdf, 2005)