Photoemission from excitons in organic semiconductors

An exciton is an atomic hydrogen-like quasi-particle, consisting of a Coulombically bound pair of an electron and a hole in conduction and valence bands, respectively. While excitons are traditionally investigated by optical spectroscopies, photoelectron spectroscopy can be a powerful tool in providing a unique view on the energetics and dynamics of excitons in semiconductor materials. The experiment typically relies on time-resolved two-photon photoemission (TR-2PPE) spectroscopy in which the first laser pulse creates excitons in a material and the second laser pulse ionizes the excitons for detection. In this short note, I discuss unique insights provided by TR-2PPE on exciton dynamics in organic semiconductors and challenges in the application of this technique.