"The development of the next generation of efficient opto-electronic devices based on organic semiconductors relies on the capability of theoretical modelling to shed light onto microscopic mechanisms underneath and provide a rational approach to materials and devices design. To answer this need, we propose the realization of a general multiscale modelling platform, capable to cover and bridge key aspects at core of device functioning, from supramolecular organization to energetics and time evolution of charge and energy carriers.This novel modelling platform will be applied to obtain crucial insights on exciton dissociation and charge separation in bulk heterojunctions, charge transport in doped materials and multiple exciton generation through fission of singlet excitons. A general and efficient computational protocol for the collection of essential information with state-of-the-art and original theoretical tools at the different levels of resolution, and its injection into effective model Hamiltonians, will endow us with an unprecedented comprehensive and realistic picture of electronic structure and dynamics in heterogeneous and disordered mesoscopic systems. Fully accounting for charge and energy carrier delocalization, intermolecular hybridization and quantum superposition of Frenkel and charge-transfer excitations, this approach has the potential to disclose molecular and supramolecular requirements for an efficient ultra-fast multiplication of excitations and their subsequent splitting through hot charge-transfer states, or for the tuning of semiconductor properties by chemical doping.This research will be undertaken in collaboration with leading experimental and theoretical groups, levering the BEST ambitious profile, and strengthening the European excellence in organic electronics research. The involvement in Host-industry partnerships will extend the BEST outreach towards applications, reinforcing the leadership of European high-tech industry."