Novel optimization principles and efficiency limits for semiconductor solar cells

Quantum efficiencies of more than merely one electron-hole pair per absorbed photon have recently been demonstrated for solar cells. The theoretical upper limit for solar cell conversion efficiency can thus be raised (from 30%) to 43% if photon absorption and electron-hole excitation follow a specific pathway. This pathway includes photon absorption at specific points in the Brillouin zone, and an inverse Auger effect mechanism for the multiplication of electron-hole pairs. We specify the principles and rules for optimal band structure tailoring.