Operando interfacial electronic properties in organic photovoltaic bulk heterojunctions

In organic photovoltaic bulk heterojunctions, the energy level alignment at donor–acceptor interfaces provides the fundamental driving force that converts strongly bound excitons into usable electrical charges. It has long been assumed—almost without question—that the interfacial energetics established under thermal equilibrium remain unchanged when the device operates under illumination. However, recent operando photoemission studies on related systems with weakly interacting interfaces have begun to challenge this assumption, pointing to the possibility that illumination can substantially alter interfacial energy levels. In this project, we will explore such non-equilibrium energetics in state-of-the-art organic photovoltaic bulk heterojunctions. To overcome their intrinsic morphological complexity, we will develop a worldwide unique methodology capable of disentangling buried interfaces with high precision. Beyond existing approaches, we will extend operando experiments towards a comprehensive suite, combining operando photoemission with operando inverse photoemission and operando electron energy-loss spectroscopy. Together, these measurements will deliver a complete picture of the occupied, unoccupied, and excitonic states under illumination. In parallel, we will establish a self-consistent theoretical framework that rationalizes the experimental findings within a single coherent description.