In conclusion, photocurrent densities up to 5.6 mA cm -2 were obtained at 0 V vs. RHE in sulfuric acid (pH=0), the highest reported value for a polycrystalline WSe 2 thin film photocathode. The high photocurrent density could be achieved by optimizing the thickness of the WSe 2 film as a function of Pd-promoter layer thickness, crystallization temperature, i.e. the deposition conditions. We have demonstrated that (NH 4 ) 2 Mo 3 S 13 (ATM) is not only an effective and earth abundant electrocatalyst for HER, but also a compound semiconductor, which after deposition on a polycrystalline and highly textured p-type WSe 2 film passivates surface states and forms a buried junction with the absorber layer, leading to a remarkable improvement of the photocatalytic activity as HER photoelectrode.