Among the various renewable sources of energy, solar energy conversion systems have been regarded as a promising way to satisfy the growing energy demand. For superior solar energy conversion performance, it is important to utilize efficient photosensitizers that have excellent light-harvesting capability. In this regard, quantum dots (QDs) are promising photosensitizer candidates owing to their high absorption coefficient, band gap tunability, and potential multiple exciton generation. Here, we report an effective and straightforward approach to improve the loadings of nanocomposite PbS/CdS QDs in a mesoporous electrode, for highly efficient solar energy conversion. By controlling the surface charge of TiO2 during the successive ionic layer adsorption and reaction process, both the PbS and CdS QD loadings are distinctly increased, leading to a highly enhanced light-harvesting capability of the photoelectrodes. This enhancement is effectively applied not only for solar-to-electrical but also for solar-to-chemical energy conversion, resulting in a ∼33% increased conversion efficiency of the QD solar cells and an unprecedented photocurrent of 22.1 mA/cm2 (at 0.6 V vs. RHE) for hydrogen production from photoelectrochemical water splitting. These results provide significant insight into the application of QD photosensitizers in solar energy conversion.