Ultrafast charge carrier dynamics in potassium-doped endohedral metallofullerene Sc3N@C80 thin films

Molecular materials have emerged as highly flexible platform for photovoltaic and light-harvesting applications. One of the most important challenges for this class of materials is the trapping of charge carriers in bound electron-hole pairs, which severely limits the free charge carrier generation. Here, we demonstrate a significant modification of the exciton dynamics in thin films of endohedral metallofullerene complexes upon alkali metal doping. For the exemplary case of ScN@C80 thin films, we show that potassium doping results in an additional relaxation channel for the optically excited charge-transfer excitons that prevents the trapping of excitons in a long-lived Frenkel exciton-like state. Instead, potassium doping leads to an ultrafast exciton dissociation and most likely to the generation of free charge carriers. In this way, we propose alkali metal doping of molecular films as a novel approach to enhance the light-to-charge carrier conversion efficiency in photovoltaic molecular materials.