Molecular semiconductors for LEDs and solar cells: designing around the Coulomb interaction (SCS and LACUS)

Pi-conjugated organic molecules and polymers now provide a set of well-performing semiconductors that support devices, including light-emitting diodes (LEDs) as used in smart-phone displays and lighting, field-effect transistors (FETs) and photovoltaic diodes (PVs).  These are attractive materials to manufacture, particularly for large-area applications where they can be processed by direct printing, so that the cost of materials and processing can be very low.   This practical success is made possible by breakthroughs in the understanding and engineering of the underlying semiconductor science.  The physics of organic semiconductors is often controlled by large electron-hole Coulomb interactions and by large spin exchange energies.  Management of excited state spin is fundamental for efficient LED and solar cells operation. I will discuss in particular recent progress in the control of emissive spin singlet excited states and non-emissive spin triplet excited states.