Ultrathin and conformal ZnS film grown by atomic layer deposition was employed in quantum dot-sensitized solar cells (QDSSCs) as an interfacial layer (IL) between mesoporous TiO2 photoanode and successive ionic layer adsorption and reaction (SILAR)-grown PbS QDs. ZnS IL provided more nucleation sites compared to a bare TiO2 photoanode, which enhanced PbS QDs loading remarkably. As a result, the optical absorbance and thus photocurrent density considerably increased. The power conversion efficiency of QDSSCs increased from 3.4% to 4% by introducing the ZnS IL. However, the beta-recombination model obtained from electrochemical impedance spectroscopy revealed the evolution of charge carrier recombination inside QDs as a consequence of enhanced QD loading, which partly dilutes this benefit.