  A 2-D photonic crystal was integrated experimentally into a thin-film
crystalline-silicon solar cell of 1-{\mu}m thickness, after numerical
optimization maximizing light absorption in the active material. The photonic
crystal boosted the short-circuit current of the cell, but it also damaged its
open-circuit voltage and fill factor, which led to an overall decrease in
performances. Comparisons between modeled and actual optical behaviors of the
cell, and between ideal and actual morphologies, show the global robustness of
the nanostructure to experimental deviations, but its particular sensitivity to
the conformality of the top coatings and the spread in pattern dimensions,
which should not be neglected in the optical model. As for the electrical
behavior, the measured internal quantum efficiency shows the strong parasitic
absorptions from the transparent conductive oxide and from the back-reflector,
as well as the negative impact of the nanopattern on surface passivation. Our
exemplifying case, thus, illustrates and experimentally confirms two
recommendations for future integration of surface nanostructures for light
trapping purposes: 1) the necessity to optimize absorption not for the total
stack but for the single active material, and 2) the necessity to avoid damage
to the active material by pattern etching.
