Self‐Hybridized Exciton‐Polariton Photodetectors From Layered Metal‐Organic Chalcogenolates

ABSTRACT Exciton‐polaritons (EPs) arising from strong light‐matter coupling offer new pathways for controlling optoelectronic properties. While typically requiring closed optical cavities for strong coupling, we demonstrate that 2D metal‐organic chalcogenolates (MOCs), mithrene (AgSePh), with a high refractive index (≈2.5) and strong excitons enable self‐hybridized polariton photodetectors (PDs) without top mirrors, simplifying device architecture. Through thickness‐tuned multimode polariton engineering, we achieve photodetection of sub‐bandgap photons via lower polariton states, validated through reflectance, photoluminescence (PL), and photocurrent spectroscopy with quantitative theoretical agreement. Trap‐assisted two‐photon absorption enables sustained strong coupling even under sub‐bandgap excitation. The polariton dispersion yields ultrafast group velocities (≈65 µm ps −1 ), extending exciton diffusion lengths from hundreds of nanometers to several micrometers. Strong‐coupling devices demonstrate a 2.38‐fold enhancement in photo‐to‐dark current ratio compared to weak‐coupling counterparts, establishing a practical route to polariton‐enhanced photodetection and light harvesting.