First-principles calculations are performed to explore the geometry, bonding, and electronic structures of six ultrathin photovoltaic heterostructures consisting of pristine and B- or N-doped fullerenes and MoS₂ or WS₂ monolayers. The fullerenes prefer to be attached with a hexagon parallel to the monolayer, where B and N favor proximity to the monolayer. The main electronic properties of the subsystems stay intact, suggesting weak interfacial interaction. Both the C₆₀/MoS₂ and C₆₀/WS₂ systems show type-II band alignments. However, the built-in potential in the former case is too small to effectively drive electron–hole separation across the interface, whereas the latter system is predicted to show good photovoltaic performance. Unfortunately, B and N doping destroys the type-II band alignment on MoS₂ and preserves it only in one spin channel on WS₂, which is unsuitable for excitonic solar cells. Our results suggest that the C₆₀/WS₂ system is highly promising for excitonic solar cells.