Abstract:
This study focuses on the influence of interface modifiers on the charge transport of hybrid nanoporous
titanium dioxide (TiO2)/poly(3-hexylthiophene) (P3HT) nanocomposites by using the time of flight
technique. We found that the hole-mobility in the nanocomposites is about three orders of magnitude less
than that of pristine P3HT. This may be due to poor infiltration of the polymer into the highly structured
porous TiO2 which in turn obstructs the charge transport of the carriers. However, the hole-mobility in the
nanocomposites is increased by an order of magnitude when a ruthenium based dye, either Z907 or N719,
is introduced at the TiO2/P3HT interface. Surprisingly, the electron-mobility of the composite is decreased
upon dye treatment. We further observed that the hole-mobility of nanocrystalline TiO2/P3HT composites
treated with a 3-hexylthiophene derivative with a cyanoacrylic acid group [(E)-2-cyano-3-(30
,300,300 0-trihexyl-
[2,20
:50
,200:500,200 0-quaterthiophene]-5-yl)acrylicacid] (4T) increased to over 10 5 cm2 V 1 s 1
, which is
over an order of magnitude higher than the hole-mobility found in untreated nanocomposites. This
trend in hole-mobility is consistent with corresponding current density (J)–voltage (V) characteristics
under illumination of TiO2/P3HT devices with or without a dye interface layer. The higher hole-mobility
found in the 4T dye treated TiO2/P3HT nanocomposite is assigned to passivation of surface traps by the
dye as well as improved packing of the polymer with the nanocrystals through effective inter-chain
interactions of 4T with P3HT.
