Cadmium
sulfide (CdS) as a narrow-band-gap semiconductor has been
coupled in 0–15 wt % to hydrothermally grown titanium dioxide
bronze-phase (TiO2-B) nanowires (TNWs), reducing the optical
band gap from 2.96 to 2.71 eV. In CdS Q-dot-impregnated TNW/CdS composite
nanowires, absorption of light extends toward the visible range of
the solar spectrum and effective light-harvesting improves via increased
specific surface area; furthermore, the properly aligned band edges
between CdS and TiO2-B ascertain efficient separation of
the photogenerated charge carriers. Overall, an optimum photoanode
material characteristic has been demonstrated in TNW/CdS-10 nanocomposite
that achieves a typical photovoltaic (PV) conversion efficiency, η
∼ 1.63%, in Q-dot-sensitized solar cells (QDSSCs), compared
to the η ∼ 0.86% of the simple electrochemical cell with
a pristine TNW photoanode. N3 dye sensitization of the pristine TNW
photoanode leads to a conversion efficiency of η ∼ 3.88%
in dye-sensitized solar cells (DSSCs). When the CdS Q-dot-sensitized
TNW/CdS-10 photoanode is further co-sensitized by the N3 dye, an enhanced
PV conversion efficiency of η ∼ 8.04% is attained in
the “Q-dot co-sensitized DSSC” device by virtue of the
optimum light absorption facilitated by the maximum dye-loading capacity
retained by the widest available surface area on the composite photoanode,
contributing to a superior incident-photon-to-current conversion efficiency
(IPCE) of ∼ 69.60% at 520 nm. Interfacial electron injection
and the recombination dynamics of the cells studied using impedance
spectroscopy demonstrate that the DSSC performance increases due to
minimization of the electron–hole recombination rate and the
increase of the conduction of charge carriers via reduced charge-transfer
resistance of the photoanode(Q-dots/dye)/electrolyte interface at
an optimum 10 wt % CdS loading. Sequential sensitization of TiO2-B nanowire photoanodes via CdS Q-dot impregnation and further
by N3 dye molecule adsorption improves light-harvesting, facilitates
efficient photocarrier generation, and prevents interfacial charge
recombination, and their cumulative electron injection results in
a better photovoltaic performance via novel “CdS Q-dots and
N3 dye co-sensitization of TiO2-B NWs” in Q-dot
co-sensitized DSSCs.
A facile one-step
hydrothermal method was developed to prepare
reduced graphene oxide-laminated TiO
2
–bronze (TiO
2
-B) nanowire composites (TNWG), which contain two-dimensional
graphene oxide nanosheets and TiO
2
-B nanowires. In the
hydrothermal process, the functional groups of graphene oxide were
reduced significantly. Dye-sensitized solar cells (DSSCs) were fabricated
using TNWG as the photoanode material. The effects of different reduced
graphene oxide contents in TNWG on the energy conversion efficiency
of the dye-sensitized solar cells were investigated using
J
–
V
and incident photon-to-current
conversion efficiency characteristics. DSSCs based on a TNWG hybrid
photoanode with a reduced graphene oxide content of 8 wt % demonstrated
an overall light-to-electricity conversion efficiency of 4.95%, accompanied
by a short-circuit current density of 10.41 mA cm
–2
, an open-circuit voltage of 0.71 V, and a fill factor of 67%, which
were much higher than those of DSSC made with a pure TiO
2
-B NW-based photoanode. The overall improvement in photovoltaic performance
could be associated to the intense visible light absorption and enhanced
dye adsorption because of the increased surface area of the composite,
together with faster electron transport due to reduced carrier recombination.
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