Novel Semiconductors for High Efficiency Photovoltaics

Monolithically-integrated III-V multijunction solar cells have the potential to reach very high efficiencies, especially for devices with 4+ junctions. Typical 3 junction solar cells are commonly grown on GaAs or Ge substrates. However, the general lack of lattice-matched III-V semiconductors with bandgaps below 1.4 eV has forced device growth to be carried out via metamorphic or multiple substrate approaches. One potential route to designing optimal low bandgap materials is to alloy GaAs with Bi. Dilute concentrations of Bi induce a strong reduction in the bandgap ($\sim$88 meV/\% Bi) with only a small change in the lattice constant. If co-doped with N, this alloy can be lattice-matched to GaAs with bandgaps spanning the range of 0 – 1.43 eV. In this talk, I will discuss the growth and physics of GaAsBi alloys. I will also highlight the promise and challenges of incorporating these materials into multijunction solar cells and the further research and development that is needed to realize high performance devices.