Charge carrier photogeneration, drift and recombination in thin film networks of polymer-wrapped (6,5)-single-wall carbon nanotubes (SWNTs) blended with phenyl-C61-butyric acid methyl ester (PCBM) have been investigated by using transient photocurrent and time-delayed collection field (TDCF) techniques. Three distinct transient photocurrent components on the nano- and microsecond timescales have been identified. We attribute the dominant (>50% of total extracted charge) ultrashort photocurrent component with a decay time below our experimental time-resolution of 2 ns to the intratube hole motion. The second component on the few microsecond timescale is attributed to the intertube hole transfer, while the slowest component is assigned to the electron drift within the PCBM phase. The hole drift distance appears to be limited by gaps in the nanotube percolation network rather than by hole trapping or recombination. Photocurrent saturation was observed when excitation densities reached more than one charge pair per nanotube; we attribute this to the local electric field screening.

Here we investigate charge carrier generation and extraction processes in hybrid polymer/nanocrystal solar cells by means of time-resolved optical and photoelectrical techniques. We addressed the role of both poly(3-hexylthiophene) and colloidal arenethiolate-capped PbS quantum dots, which constitute the hybrid composite nanomaterial, in the photoinduced processes most relevant to device operation by changing the compositional ratio and applying chemical and thermal postdeposition treatments. The carrier generation processes were found to be wavelength-dependent: excitons generated in the polymer domains led to long-lived weakly bound charge pairs upon electron transfer to PbS nanocrystals; whereas charge carrier generation in the nanocrystal domains is highly efficient, although effective separation required the application of external electric field. Overall, charge carrier generation was found efficient and almost independent of the strength of applied electric field; therefore, competition between separation of electron−hole pairs into free carriers and geminate recombination is the major factor limiting the fill factor of nanocomposite-based solar cells. Device efficiency improvements thus require faster interfacial charge transfer processes, which are deeply related to the refinement of nanocrystal surface chemistry.