Abstract: Quantum confined semiconductor nanocrystals (0D quantum dots, 1D quantum rods and 2D quantum wells) have been intensively investigated as light harvesting and charge separation materials for photovoltaic and photocatalytic applications. The efficiency of these semiconductor nanocrystal-based devices depends on many fundamental processes, including light harvesting, carrier relaxation, exciton localization and transport, charge separation and charge combination. The competition between these processes determines the overall solar energy conversion (solar to electricity or fuel) efficiency. Quantum confined semiconductor nano-heterostructures, combining two or more material components, offer unique opportunities to control their charge separation properties by tailoring their compositions, dimensions and spatial arrangement. Further integration of catalysts (heterogeneous or homogeneous) to these materials form multifunctional nano-heterostructures. Using 0D, 1D and 2D CdSe/CdS/Pt heterostructures as model systems, we directly probe the abovementioned fundamental exciton and carrier processes by transient absorption and time-resolved fluorescence spectroscopy. We are examining how to control these fundamental processes through the design of heterostructures to achieve long-lived charge separation and efficient H2 generation. In this talk, we will discuss the mechanism of 2D exciton transport, dissociation and annihilation in nanosheets and key factors limiting H2 generation efficiency in CdS/Pt nanosheet heterostructures.