The effect of semiconductor passivation on quantum-dot-sensitized solar cells (QDSCs) has been systematically characterized for CdS and CdS/ZnS. We have found that passivation strongly depends on the passivation agent, obtaining an enhancement of the solar cell efficiency for compounds containing amine and thiol groups and, in contrast, a decrease in performance for passivating agents with acid groups. Passivation can induce a change in the position of TiO 2 conduction band and also in the recombination rate and nature, reflected in a change in the ÎČ parameter. Especially interesting is the finding that ÎČ, and consequently the fill factor can be increased with the passivation treatment. Applying this strategy, record cells of 4.65% efficiency for PbS-based QDSCs have been produced. SECTION: Energy Conversion and Storage; Energy and Charge Transport I n the past few years, the interest in the use of light-absorbing inorganic semiconductor materials for nanostructured photovoltaic devices has increased enormously, in particular, in the case of semiconductor quantum dots (QDs), when the semiconductor particle size is smaller than its Bohr radius and quantum confinement regime is attained. 1â7 These materials are extremely interesting for the development of photovoltaic applications for several reasons: tunable band gap, high extinction coefficient, large intrinsic dipole moment, and easy and cheap production.