Finding
the material characteristics satisfying most of the photovoltaic
conditions is difficult. In contrast, utilization of foreign materials
that can contribute to light harvesting and charge transfers in the
devices is now desirable/thought-provoking. Herein, a binary hybrid
photoanode utilizing nano-amassed micron-sized mesoporous zinc oxide
hollow spheres (meso-ZnO HS) in conjunction with SnO
2
nanoparticles
(NPs), i.e., SnO
2
NP_ZnO HS (for an optimized weight ratio
(8:2)), displayed a nearly ∼4-fold increase in the efficiency
(η) compared to that of bare SnO
2
nanoparticle device.
Enhanced device efficacy in the composite photoanode-based device
can be accredited to the dual function of nano-amassed meso-ZnO HS.
Nano-amassed micron-sized ZnO HS embedded in the photoanode can increase
the light-harnessing capability without sacrificing the surface area
as well as optical confinement of light by multiple reflections within
its cavity and enhanced light-scattering effects. Electrochemical
impedance spectroscopy analysis revealed an extended lifetime of electron
(τ
e
) and a higher value of
R
ct2
at the working electrode/dye/redox mediator interface,
indicating a minimum photoinduced electron interception. The open-circuit
voltage decay reveals a slower recombination kinetics of photogenerated
electrons, supporting our claim that the nano-ammased meso-ZnO HS
can serve as an energy barrier to the photoinjected electrons to retard
the back-transfer to the electrolyte. Moreover, the improvement in
the fill factors of the composite-based devices is endorsed to the
facile penetration of the electrolyte through the pores of nano-amassed
meso-ZnO HS, which increases the regeneration probability of oxidized
dyes.