  Dye-sensitized solar cells (DSSCs) are gaining considerable interest as
alternatives to the semiconductor-based thin film solar cells. The noble metal
platinum (Pt) is conventionally used as counter electrode (CE) material for
fabricating DSSCs. Since Pt is expensive and scarce, new materials have been
explored to develop cost-effective Pt-free counter electrodes for DSSCs.
Two-dimensional (2D) graphene-based counter electrodes have achieved the
highest known power conversion efficiency ({\eta}) of 13%, which has stimulated
research activities in 2D layered transition metal dichalcogenides (TMDs) for
developing Pt-free DSSCs. In this review, progress made on alternative counter
electrodes for fabricating low-cost Pt-free DSSCs, based on earth-abundant 2D
TMDs including MoS2, WS2, TiS2, FeS2, CoS2, NiS2, SnS2, MoSe2, NbSe2, TaSe2,
NiSe2, FeSe2, CoSe2, Bi2Se3 and their based composites, are discussed and
summarized. Also, the considerable progress made on thin films of MoS2 and MoS2
based carbon, graphene, carbon nanotubes (CNTs), carbon nanofibers (CNFs), and
poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composites
as efficient counter electrodes (CEs) for DSSCs are discussed, in terms of
their electrochemical and photovoltaic properties. At present, PCE values
higher than that of standard Pt CE have been recorded for a number of TMD-based
CEs, which include MoS2 and MoSe2/thin films deposited on Mo foil, MoS2/CNTs,
MoS2/graphene, MoS2/carbon, MoSe2/PEDOT:PSS, NbSe2, FeS2, FeSe2 nanosheets,
TiS2/graphene, and NiS2/graphene hybrid systems in DSSCs, for the reduction of
triiodide (I3-) to iodide (I-). The highest PCE ({\eta}=10.46%) versus Pt CE
({\eta}=8.25%) at 1 Sun (100 mW/cm2, AM 1.5G) was measured for DSSCs having a
low cost and flexible CoSe2/carbon-nanoclimbing wall counter electrode
deposited on a nickel foam.
