Effect of Doping on Photoinduced Charge Carrier Dynamics of Semiconducting Polymer, Poly(benzo(1,2-<i>b</i>:4,5-<i>b</i>′)dithiophene-<i>alt</i>-dione) (PBDB-T), in Photoelectrochemical Cells

Photoelectrochemical cells based on polymer semiconductors are a viable platform for solar-to-fuel conversion, yet optimizing photogenerated charge transport remains a key challenge. Understanding and controlling these charge carrier dynamics are critical for advancing device efficiency. Here, we report that electrochemical doping of a semiconducting polymer, poly(benzo(1,2-<i>b</i>:4,5-<i>b</i>')dithiophene-<i>alt</i>-dione) (PBDB-T), effectively enhances photoelectrochemical activity. We systematically investigate the influence of doping species (Cl^-, Br^-, and I^-) on charge carrier dynamics using intensity-modulated photocurrent spectroscopy (IMPS). Our results indicate that (1) all halide dopants accelerate both charge transfer and recombination kinetics, (2) the greater relative increase in the charge transfer rate leads to an overall improvement in charge transfer efficiency, and (3) Cl^- doping yields the highest photocurrent enhancement, which is attributed to efficient exciton separation. These findings provide valuable insight into how dopant identity influences charge carrier dynamics and offer a strategy for designing high-performance organic photoelectrodes through controlled electrochemical doping.