  The honeycomb connection of carbon atoms by covalent bonds in a macroscopic
two-dimensional scale leads to fascinating graphene and solar cell based on
graphene/silicon Schottky diode has been widely studied. For solar cell
applications, GaAs is superior to silicon as it has a direct band gap of 1.42
eV and its electron mobility is six times of that of silicon. However,
graphene/GaAs solar cell has been rarely explored. Herein, we report
graphene/GaAs solar cells with conversion efficiency (Eta) of 10.4% and 15.5%
without and with anti-reflection layer on graphene, respectively. The Eta of
15.5% is higher than the state of art efficiency for graphene/Si system
(14.5%). Furthermore, our calculation points out Eta of 25.8% can be reached by
reasonably optimizing the open circuit voltage, junction ideality factor,
resistance of graphene and metal/graphene contact. This research strongly
support graphene/GaAs hetero-structure solar cell have great potential for
practical applications.
