  Photoreflectance (PR) is a convenient characterization tool able to reveal
optoelectronic properties of semiconductor materials and structures. It is a
simple non-destructive and contactless technique which can be used in air at
room temperature. We will present experimental results of the characterization
carried out by means of PR on different types of advanced photovoltaic (PV)
structures, including quantum-dot-based prototypes of intermediate band solar
cells, quantum-well structures, highly mismatched alloys, and III-V-based
multi-junction devices, thereby demonstrating the suitability of PR as a
powerful diagnostic tool. Examples will be given to illustrate the value of
this spectroscopic technique for PV including (i) the analysis of the PR
spectra in search of critical points associated to absorption onsets; (ii)
distinguishing signatures related to quantum confinement from those originating
from delocalized band states; (iii) determining the intensity of the electric
field related to built-in potentials at interfaces according to the
Franz-Keldysh (FK) theory; and (v) determining the nature of different
oscillatory PR signals among those ascribed to FK-oscillations, interferometric
and photorefractive effects. The aim is to attract the interest of researchers
in the field of PV to modulation spectroscopies, as they can be helpful in the
analysis of their devices.
