Implementing a photodetector into an optical cavity, e.g. a Fabry-Pérot resonator, leads to a confinement of the electromagnetic field and an alteration of the emission rate of the photoactive material. By tuning the length of the cavity, optical transitions in resonance with a cavity mode are selectively amplified (Figure ). This coupling can have several advantageous effects for fast photodetection, such as the tuning of the lifetime of the photoexcited state or an increased carrier mobility. The latter has been demonstrated for a perylene diimide derivative and resulted in an increase of one order of magnitude, presumably due to a polariton-mediated delocalization of excitons. For the coupling to be strong, it is important that the reabsorption of emitted photons is efficiently possible, which favors materials with small Stokes shifts, such as WS2. One can expect that strong coupling between photodetector and optical cavity will drastically enhance the speed and efficiency of the device, which is the basis for the emerging field of polaritonic chemistry. 39