Carbon nanotubes (CNTs) have been attracting strong attention owning to their fascinating one-dimensional structure
and unique mechanical, electrical and thermal properties. CNTs are promising in various important applications, but
their application is severely impeded by their poor processibility, since they do not melt and usually have quite low
solubility in solvents. The methods reported in literature for the dispersion of CNTs require an ultrasonication of CNTs
under a high power or a chemical reaction, which can alter the physical properties and bring severe defects to CNTs.
They are still far away from processing of CNTs in large scale, because only in a small amount of CNTs can be
dispersed by these methods. Here, we will report a simple and efficient method to directly disperse CNTs in nonionic
surfactants. CNTs and a nonionic surfactant form gels by mechanical grinding. The gels can be processed into CNT
films by coating. The CNT films have good adhesion to the substrates and do not detach from the substrate after several
weeks. We also demonstrate that the CNT films prepared by our method can be used as the counter electrode of highperformance
dye-sensitized solar cells (DSCs). The photovoltaic efficiency is comparable to the devices using conventional noble platinum as the counter electrode.
Two novel approaches are reported to significantly enhance the conductivity of transparent PEDOT:PSS
(PEDOT:PSS = poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)). The first method is to add anionic surfactants into aqueous
solution of PEDOT:PSS. Conductivity enhancement by a factor of hundreds was observed, and it was strongly dependent
on the chemical structure of the surfactant. Conductivity enhancement from 0.16 S cm-1 to 80 S cm-1 was observed, when
anionic surfactant SDS was added. The effect of the anionic surfactants on the conductivity of PEDOT:PSS was
attributed to the substitution of the PSS anions by the surfactant anions. The addition of a nonionic surfactant had
moderate effect on the conductivity of PEDOT:PSS, while cationic surfactant almost did not affect the conductivity. The
second method to significantly enhance the conductivity is to treat the PEDOT:PSS film with solutions of certain salts.
CuCl2 or InCl3 solution could enhance the conductivity by a factor of hundreds, while the effect by NaCl is negligible.
The salt effect on the conductivity of PEDOT:PSS is attributed to the loss of PSS from PEDOT:PSS and conformational
change of PEDOT chains during the treatment.
High-performance dye-sensitized solar cells (DSCs) with nanocomposites as counter electrode are reported, since
nanomaterials have high specific surface and could have high catalysis. Nanocomposites of carbon nanotubes (CNTs)
and conducting PEDOT:PSS (PEDOT:PSS = poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) were prepared
by dispersing CNTs in aqueous solution of PEDOT:PSS. The dispersion is related to the π-π interaction between CNTs
and conjugated PEDOT, which is stabilized by the excess PSS in water. Nanocomposite films of CNTs and PEDOT:PSS
could be prepared by solution processing. They could have high transparency and high conductivity. Nanocomposite
films prepared by drop casting at room temperature were used as the counter electrode of DSCs. The devices exhibited
high photovoltaic performance with the energy conversion efficiency of 6.5%, short-circuit current of 15.5 mA cm-2,
open-circuit voltage of 0.66 V, and fill factor of 0.63 under AM1.5 sun light. This performance is close to the devices
using conventional platinum as the counter electrode.
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