Self-Hybridized Exciton-Polariton Photovoltaics

Emerging excitonic semiconductors are attractive for next generation photovoltaics (PVs) with low cost, weight, and materials consumption. However, the exciton diffusion required for photocurrent generation is generally a source of inefficiency due to the localized nature of excitons. In contrast, the strong coupling of excitons to cavity photons produces hybrid light-matter states called exciton-polaritons, which are delocalized and have low effective mass due to the photonic component. We show that strong coupling of excitons to cavity photons in a bulk WS₂ absorber layer, serving as both the optical cavity and excitonic material, can enhance the external quantum efficiency (by a factor of >10) and power conversion efficiency (by a factor of ~3) of photovoltaics. We use varying WS₂ thickness to change the cavity energy and show that enhanced efficiency is due in part to enhanced exciton transport enabled by strong coupling. Remarkably, the enhanced transport occurs for on- and off-resonant excitation, underscoring the importance and practicality of the self-hybridized system, which can simultaneously enable broadband absorption and polariton-enhanced transport. This result offers a path towards efficient excitonic optoelectronics and energy conversion devices.