Credit: Image used with permission from Physical Review Letters. ©2014 by the American Physical Society
Absorption of sunlight in silicon solar cells results in losses due to heat from “hot” photo-excited electrons. Electrons in solids occupy energy levels called electronic bands, for example, the electronic band structure of silicon is shown. “Hot” photo-excited electrons have excess energy and lose this energy to heat rather than producing electricity. A leading mechanism of this detrimental heating consists of electron-phonon scattering processes. Colored maps of the broadening of energy levels due to scattering (in units of meV) as well as relaxation times for photo-excited electrons are overlaid on the band structure. Such new understanding of losses from heating could lead to more efficient solar cells.