. The different role played by the CdS layer in PbS/CdS design could be that it can function as a passivation layer in minimizing the surface defects in PbS q-dots. For the verification of surface passivation properties of CdS on PbS surface, we performed photovoltage decay measurements and electrochemical impedance spectroscopy measurements of PbS/CdS photoanode with different thicknesses of PbS and CdS.