  This work addresses the integration of reflectarray antennas (RA) on thin
film Solar Cell (SC) panels, as a mean to save real estate, weight, or cost in
platforms such as satellites or transportable autonomous antenna systems. Our
goal is to design a good RA unit cell in terms of phase response and bandwidth,
while simultaneously achieving high optical transparency and low microwave
loss, to preserve good SC and RA energy efficiencies, respectively. Since there
is a trade-off between the optical transparency and microwave surface
conductivity of a conductor, here both standard copper and transparent
conductors are considered. The results obtained at the unit cell level
demonstrates the feasibility of integrating RA on a thin-film SC, preserving
for the first time good performance in terms of both SC and RA efficiency. For
instance, measurement at X-band demonstrate families of cells providing a phase
range larger than 270{\deg} with average microwave loss of -2.45dB (resp.
-0.25dB) and average optical transparency in the visible spectrum of 90% (resp.
85%) using transparent conductive multilayer (resp. a copper layer).
