. Following this rationale, it is not surprising that p(NDI-T) and p(NDI-T2 P75) exhibit comparable HPPR activity (Figure ). Here, however, it is unclear whether polaron formation remains rate-limiting and the observed increase in current relative to p(NDI-T2 P75) may be due to a larger capacity of reactive electrons in the film or from a difference in electrochemically active surface area.