Tunable Charge Transfer Dynamics at Tetracene/LiF/C60 Interfaces*

Organic conducting polymers offer an attractive alternative to regular semiconductors in both photovoltaic and optoelectronic applications due to their low cost and improved processability. Although current organic devices suffer from relatively low electro-optical conversion efficiency, novel polymer nanocomposites, both organic/organic and organic/inorganic, should provide better control over the material properties and improve the device performance. In such nanocomposites, physical and electronic structures of the interfaces govern carrier generation and transport characteristics yet underpinning mechanisms are still poorly understood. Here, we apply ultrafast optical spectroscopy to observe an interfacial charge transfer dynamics in Tc/LiF/C60 multilayered heterostructures, where charge separation processes compete with parasitic radiative and non-radiative charge transfer exciton recombination. Our studies reveal that the tunneling barrier created by LiF buffer layer between donor and acceptor materials provides means for independent control over the rates of direct and diffusion-induced charge transfer exciton formation and recombination dynamics. These findings might have implications for development of more efficient organic photovoltaic and light-emitting devices.