We replaced the nanoparticle film with a dense, oriented
array of crystalline ZnO nanowires grown using zinc nitrate,
HMTA, and PEI in water. Using a ZnO nanowire array with
one-fifth the surface area of a nanoparticle DSC, a full sun
efficiency of 1.5% was demonstrated.7 Figure 8B is a plot
of the current density versus voltage (J-V) for our two best
devices with roughness factors (defined as the total film area
per unit substrate area) of ∼200. Nanoparticle films typically
have a roughness factor of ∼1000. The external quantum
efficiency (EQE) of these cells peaks at ∼40% near the
absorption maximum of the dye molecule {[cis-bis(thiocyanato)-N,N′-bis(2,2′′-bipyridyl-4,4′-dicarboxylate)ruthenium-
(II) bis(tetrabutylammonium)], also known as N719}. The
EQE is mainly limited by the low dye loading of the
nanowire films because of a relatively small roughness factor.
To understand the relative electron transport of the
nanowire cell versus the nanoparticle cell, it is best to
compare the short-circuit current density (JSC) rather than