<p>Photodiodes are central to high-speed communication, sensing and light-harvesting devices. While silicon and other inorganic semiconductor-based photodiodes have been widely integrated into commercial technologies, photodiodes from excitonic semiconductors continue to maintain high interest in research. Excitonic semiconductors are superior in terms of absorption as compared to silicon and III-V semiconductors, but have always suffered from poor charge transport and narrow band absorption due to the short diffusion lengths and resonant nature of the excitons, respectively. Here, we attempt to solve both these central issues in excitonic photodiode devices via use of polariton physics and demonstrating photodiodes in the strong light-matter coupling regime. By using a conductive tin-doped indium oxide transparent top electrode that also serves as an anti-reflective coating combined with self-trapping and hybridization of light in inorganic excitonic semiconductor WS₂, we demonstrate photodiodes with broadband absorption and internal quantum efficiency values approaching unity near the zero-detuning condition. Furthermore, it is demonstrated that the response speed of photodiodes is enhanced under strong coupling. Our work presents a promising approach to explore the physics and applications of photodiodes based on excitonic semiconductors.</p>