Abstract:
Self-assembled monolayers (SAMs) of benzoic
acid based molecules are used to modify the metal oxide–
polymer interface in a hybrid poly-3-hexylthiophene
(P3HT)/TiO2 photovoltaic device structure. The effect of
SAMs on current density is in accordance with expectation
from the driving force for charge separation of metal
oxide–polymer interface in a hybrid poly-3-hexylthiophene
(P3HT)/TiO2 photovoltaic device. However, the effect of
monolayers on open circuit voltage is quite unexpected
from the interfacial energetics as all the monolayers
improve the open circuit voltage in spite of different sign of
the interfacial dipole for different SAMs. This suggests that
the monolayers have additional functions. Overall device
performance is enhanced by more than a factor of two
using a SAM with permanent dipole pointing towards the
TiO2 surface or pointing towards polymer when compared
to a control device with no interface modifiers. This study
concludes that the SAM layer has two functions that are to
shift the position of the conduction band of the porous TiO2
relative to the polymer HOMO level so as to influence
interfacial charge separation and to act as a barrier layer,
insulating back electron transfer from the TiO2 to the
polymer. Both effects can benefit the performance of
hybrid polymer metal oxide solar cells.
