Upon comparing the IPCE spectra of the samples prepared at 240°C and 300°C (Figure (b)) the explanation of the observed potential dependence of the blue photons for the 240°C sample can be further assessed. As mentioned above, due to the different growth temperature, the path length for charge carriers to be collected inside the rod-like grains for the 300°C samples is more than 10 times greater than those of the lower temperature samples (Figure ). The onset of the IPCE at wavelengths 680-740 nm (photogenerated charge carriers produced near the back contact) is similar for both sulfurization temperatures. For shorter wavelengths though, the photon to current conversion efficiency decreases for the 300°C sample (Figure ). This observation is consistent with a charge collection problem at the back contact for the photogenerated holes, due to the longer distance that the charge carriers must travel through the rod-like micron sized grains. It is worth noting that, despite having an unfavorable band bending at the heterojunction interface (Figure ), the Sb2S3 photocathodes does inject significant photoelectrons into the TiO2 layer for water reduction. The observations also imply that upon a controlled p-type doping of the absorber (for instance with Cu) a higher built in voltage in the heterojunction can be generated.