Low-Cost Pt-Free Counter Electrode Catalysts in Dye-Sensitized Solar Cells - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 82

To achieve highly effective catalysts, Ma et al. synthesized MoC and WC
imbedded in ordered mesoporous carbon (MoC-OMC, WC-OMC) by the in situ
method [ 29 ]. The PCE values of the DSCs reached 8.18 % (WC-OMC) and
8.34 % (MoC-OMC), much higher than those of the DSCs using WC (5.35 %)
and Mo 2 C (5.70 %) CEs. Further, they prepared WO 2 and Ni 5 P 4 imbedded in
mesoporous carbon and both the composite CEs catalysts showed high catalytic
activity [ 48 , 49 ]. Gao et al. deposited TiN nanoparticles on CNTs (TiN/CNTs) and
then used the composite as a CE in DSC which produced a PCE of 5.41 %, higher
than both the DSCs using TiN CE (2.12 %) and pure CNTs CE (3.53 %) [ 50 ]. The
high catalytic activity can be attributed to the combination of the high catalytic
activity and the high electrical conductivity into one composite. This strategy can
be used to design effective catalysts in the future research. Park et al. prepared
W 2 C/WC composite CE in DSC, resulting in a PCE of 4.2 %, still lower than that
of Pt (5.22 %) [ 51 ]. Wu et al. introduced the Pt/Cb composite catalyst into DSCs.
Loading 1.5 wt% Pt on Cb was enough to achieve high catalytic activity and the
DSC gave a PCE of 6.72 % [ 52 ]. Ouyang et al. prepared PEDOT-PSS/CNTs and
PSS/CNTs composite CEs [ 53 ]. The DSC using PEDOT-PSS/CNTs CE yielded a
PCE of 6.5 %, much higher than that of the DSC using PSS/CNTs CE (3.6 %).
Kang et al. used CoS/PEDOT/PSS as a composite CE catalyst, with the corre-
sponding DSC giving a PCE of 5.4 %, comparable to that of the DSC using Pt CE
(6.1 %). The high catalytic activity of this composite CE can be attributed to the
synergistic catalytic effect [ 54 ]. Lin et al. synthesized MoS 2 /Graphene composite
as CE in a DSC, which gave a PCE of 6.04 %, slightly lower than that of the DSC
using Pt CE [ 55 ].
On current evidence, prepared composite has become an effective path to
achieve CE catalysts for DSCs. However, the mechanism of high catalytic activity
and the roles of the catalyst and the supporter are still in dispute.
5 Summary
In sum, a series of Pt-free CE catalysts have been introduced into DSCs, each with
unique advantages and disadvantages. We think that carbon material is the most
potential substitute to Pt in DSCs. Organic polymers offer a promising alternative
as flexible and transparent CEs. In addition, the introduction of transition metal
carbides, nitrides, oxides, sulfides, selenides, and phosphides into DSCs widens the
selective scope of CE catalysts remarkably. Combining two or more proper
materials into one composite is an effective path to design high-efficiency catalysts
for DSCs. Now, to develop low-cost Pt-free CE catalysts has become a hot
research topic to reduce the cost of DSCs, which makes DSCs more competitive
among various photovoltaic devices, contributing to realize the industrialization of
DSCs.