  Excitonic semiconductors are attractive for next-generation photovoltaics
(PVs) with lower cost, lighter weight, and lower material consumption than
conventional technologies. Among them, transition metal dichalcogenide
materials like WS2 are especially interesting due to exceptionally strong
light-matter interaction. Photocurrent generation in excitonic PVs relies on
exciton diffusion to heterointerfaces. However, efficiencies of excitonic PVs
are often limited by short exciton diffusion lengths. Here we report that the
strong coupling of excitons to cavity photons in a WS2 absorber layer can
enhance the external quantum efficiency by a factor of >10, internal quantum
efficiency by a factor of ~3, and power conversion efficiency of excitonic PVs
by an order of magnitude. The resulting hybrid states, exciton-polaritons,
enhance the resonant absorption and exciton transport while the use of the WS2
layer as its own optical cavity enables broadband absorption. Thickness
dependent device characterization reveals anomalous internal quantum efficiency
and fill factor behavior that are attributed to novel exciton-polariton
transport. Exciton-polariton enhanced transport occurs for both resonant and
off-resonant excitation, emphasizing the value and practicality of the
self-hybridized device structure. Our work presents a route towards excitonic
PVs with broadband absorption and improved exciton transport without strict
requirements of donor/acceptor structure of other excitonic PVs.
