Charge separation dynamics at bulk heterojunctions between poly(3-hexylthiophene) and PbS quantum dots

Photo-induced electron transfer between poly-(3-hexylthiophene) (P3HT) and small (2.4 nm) PbS quantum dots (QDs), capped by different ligands, was studied by picosecond and femtosecond time-resolved fluorescence and by photo-induced absorption (PIA) measurements. In line with previous experiments, we observed that the efficiency of the quenching of P3HT by PbS QDs increased upon decreasing the average thickness of the ligand shell. This trend was also observed in the PIA spectra and in prior work on the performance of photovoltaic devices where the active layer was a blend of P3HT with PbS QDs capped by different ligands. Combining the pico- and femtosecond fluorescence decays showed that the quenching in blend films of P3HT and PbS QDs treated with 1,4-benzenedithiol occurred over a broad time scale ranging from tens of femtoseconds to hundreds of picoseconds. This complex kinetics was attributed to exciton hopping followed by electron transfer to the conduction band of the QDs. We also compared the wave...