  Doping is of great importance to tailor the electrical properties of
semiconductors. However, the present doping methodologies for organic
semiconductors (OSCs) are either inefficient or can only apply to a small
number of OSCs, seriously limiting their general application. Herein, we reveal
a novel p-doping mechanism by investigating the interactions between the dopant
trityl cation and poly(3-hexylthiophene) (P3HT). It is found that electrophilic
attack of the trityl cations on thiophenes results in the formation of
alkylated ions that induce electron transfer from neighboring P3HT chains,
resulting in p-doping. This unique p-doping mechanism can be employed to dope
various OSCs including those with high ionization energy (IE=5.8 eV). Moreover,
this doping mechanism endows trityl cation with strong doping ability, leading
to polaron yielding efficiency of 100 % and doping efficiency of over 80 % in
P3HT. The discovery and elucidation of this novel doping mechanism not only
points out that strong electrophiles are a class of efficient p-dopants for
OSCs, but also provides new opportunities towards highly efficient doping of
OSCs.
