Lewis-acid doping of organic semiconductors (OSCs) opens up new ways of p-type doping and has recently become of significant interest.

Lewis acid doping of organic semiconductors (OSCs) opens up new ways of p-type doping and has recently become of significant interest. As for the mechanistic understanding, it was recently proposed that upon protonation of the OSC backbone, electron transfer occurs between the protonated polymer chain and a neutral chain nearby, inducing a positive charge carrier in the latter [Nat. Mater. 18, 1327 (2019)]. To further clarify the underlying microscopic processes on a molecular level, in the present work, we analyze the influence of protons on the electronic properties of the widely used PCPDT–BT copolymer. We find that single protonation of the polymer chain leads to the formation of a polaron coupled to the position of the proton. Upon protonation of the same chain with a second proton, an intrachain electron transfer occurs, leaving behind a polaron largely decoupled from the proton positions. We also observe the possibility of an interchain electron transfer from a neutral chain to a double protonated chain in agreement with the mechanism recently proposed in the literature. The simulated vertical excitation spectra for an ensemble of protonated species with different amounts of protons enable a detailed interpretation of experimental observation on PCPDT–BT doped with the Lewis acid BCF. Our results further suggest that multi-protonation plays an important role for completing the mechanistic picture of Lewis acid doping of OSCs.

The mechanism of charge transport in semiconducting conjugated polymers is of fundamental importance. The role of polymer dynamics therein is considered crucial but is not yet fully explored. In the present work, we combine density functional theory (DFT) and ab intio molecular dynamics (AIMD) simulations to study the dynamics-induced charge transfer (CT) in ordered bi-molecular systems of the widely investigated polymers PCPDTBT and P3HT, respectively. Our AIMD simulations capture interchain and intrachain CT providing valuable insights into polaron energetics during the CT processes. We show that interchain CT in the bi-molecular systems is induced by the vibrational dynamics and significant coupling of electrons to specific vibrational modes. We find that the polaron shared by the two neighboring molecules is energetically stabilized with respect to the single oligomer polaron; in a film environment this stabilization could make the polaron transfer to the surrounding polymer matrix less favourable. This could be an important parameter in designing efficient organic semiconductor materials. Our results provide detailed insights into charge transport mechanisms at the molecular level and illustrate the role of polaron energetics in dynamical charge transfer.