The best performing (champion) device for 240 °C sulfurized Sb2S3 photocathode is shown in Figure , where photocurrent densities of ~ 9 mA cm -2 were obtained at -0.4 V vs RHE. The incident photon to current efficiency (IPCE) spectrum was obtained at 0 V vs RHE (Figure In order to gain further understanding of the wavelength dependent charge collection of our photocathodes, bias-dependent IPCE measurements were performed on the champion Sb2S3 sample (sulfurized at 240°C) (Figure ). At positive bias (+0.05 V vs RHE), the IPCE near the band gap energy is low, increasing slowly with decreasing wavelength (from 740 nm to 400 nm).