Among
various molecular p-dopants, some Lewis acids have shown
recognizable doping effect by the formation of Lewis acid–base
adduct for increased hole concentration in organic semiconductors.
However, the doping product is often unstable in air by the interference
of water. Here near amorphous conjugated polymer poly(indacenodithiophene-co-benzothiadiazole) (IDT-BT) was doped with four Lewis
acid dopants of varying acidities, zinc-, borane-, carbonium- and
oxonium-based molecules, respectively. Bearing stronger acidity, the
oxonium dopant (C6H15O)+BF4
– yielded the most air-stable Lewis acid–base
adduct, which was confirmed by direct comparison of electron paramagnetic
resonance and UV–vis absorption spectra of the four doping
systems measured in air. A single polaron species of radical cation
was produced between the IDT-BT host and the oxonium dopant, with
a binding stoichiometry of 1:1 according to the model study using
a benzothiadiazole-derivatized molecule. Via modulating the dopant
quantity, the performance of thin-film transistors based on (C6H15O)+BF4
–-doped IDT-BT was optimized with enhanced mobility, significantly
reduced threshold voltage, higher on/off ratio, and excellent air-stability
due to the additional carriers produced by the stable Lewis acid–base
adduct. Notably, while the semiconductor layer was processed in air,
the (C6H15O)+BF4
–-doped device exhibited almost no loss of performance as compared
with that under inert atmosphere. We demonstrate that the performance
and air stability of Lewis acid-doped polymer and transistor devices
thereby can be improved by increasing the acidity of the dopant.