GaInP/GaAs/Ge Ultrahigh-Efficiency Solar Cells
This talk will discuss recent
developments in III-V multijunction photovoltaic technology which have led to
the highest-efficiency solar cells ever demonstrated. The relationship between the materials science of III-V
semiconductors and the achievement of record solar cell efficiencies will be
emphasized. For instance,
epitaxially-grown GAInP has been found to form a spontaneously-ordered GaP/InP
(111) superlattice. This ordering
affects the band gap of the material, which in turn affects the design of solar
cells which incorporate GaInP. For the
next generation of ultrahigh-efficiency III-V solar cells, we need a new
semiconductor which is lattice-matched to GaAs, has a band gap of 1 eV, and has
long minority-carrier diffusion lengths.
Out of a number of candidate materials, the recently-discovered alloy
GaInNAs appears to have the greatest promise.
This material satisfies the first two criteria, but has to date shown
very low diffusion lengths, a problem which is our current focus in the
development of these next-generation cells.