  Graphene has been intensively studied in photovoltaics focusing on emerging
solar cells based on thin films, dye-sensitized, quantum dots, nanowires, etc.
However, the typical efficiency of these solar cells incorporating graphene are
below 16%. Therefore, the photovoltaic potential of graphene has not been
already shown. In this work the use of graphene for concentration applications
on III-V multijunction solar cells, which indeed are the solar cells with the
highest efficiency, is demonstrated. Firstly, a wide optoelectronic
characterization of graphene layers is carried out. Then, the graphene layer is
incorporated onto triple-junction solar cells, which decreases their series
resistance by 35% (relative), leading to an increase in Fill Factor of 4%
(absolute) at concentrations of 1,000 suns. Simultaneously, the optical
absorption of graphene produces a relative short circuit current density
decrease in the range of 0-1.8%. As a result, an absolute efficiency
improvement close to 1% at concentrations of 1,000 suns was achieved with
respect to triple junction solar cells without graphene. The impact of
incorporating one and two graphene monolayers is also evaluated.
