Because of their ultrathin nature, the optoelectronic, photonic and quantum properties of layered two-dimensional (2D) semiconductors are highly responsive to changes in free-carrier density, making it imperative to masterfully control their doping levels. We report a new photo-doping scheme that quasi-permanently modifies monolayer MoS2 carrier density to extents previously only achievable on ultrafast timescales or in electrically connected devices. The enhanced performance is enabled by coupling monolayer MoS2 with indium tin oxide (ITO) nanocrystals demonstrating the remarkable ability to store multiple electrons per nanocrystal. When this hybrid system is illuminated with UV radiation, MoS2 electrons are transferred to the photo-generated unoccupied valence band states in the nanocrystals, effectively photo-doping the n-type MoS2 with holes. MoS2 photoluminescence reveals that the dominant exciton species evolves from trions to neutral excitons, evidence of electron extraction from the MoS2. Reductions in carrier density by approximately 6×1012 cm-2 are observed, and spatial-dependent measurements reveal long-range changes proliferating up to 40 µm away from a localized point of photodoping. Single ITO nanocrystals in this simple architecture can store upwards of 40 electrons. These studies reveal a new all-optical method to control the carrier density in 2D semiconductors, enabling unprecedented manipulation of their optoelectronic properties and innovative energy storage technologies.