Exploiting Charge Transfer States in Molecular and Organic Electronics

The growing demand for smaller, faster, and more versatile electronics has led to a surge of interest in new device concepts. One promising approach is to exploit the charge-transfer (CT) state that forms at the interface between charge donor and acceptor molecules. However, establishing reliable relationships between donor/acceptor molecular structures, the resulting CT, and physical properties is challenging. In this talk, the implications of the hybrid electronic states will be discussed by examining two model systems: a monolayer of co-assembled molecules with strong electron donor and acceptor termini, and a polymorphic system based on a donor/acceptor charge transfer salt in the form of single crystals with varying donor-acceptor overlap. In the molecular rectifiers based on self-assembled molecules, the charge transfer state is responsible for the observed increase in the rectification ratio, despite the reduction caused in the film degree of order. These high-performance molecular diodes have been employed in circuits to effectively rectify an AC signal. In the single crystals, we correlate the solid-state packing with the degree of charge transfer and the resulting electrical properties. We also probe the sub-gap, trap states, through the measurement of field-effect transistors, an analysis which has so far seen little application in ambipolar devices. Our results provide evidence that small differences in donor/acceptor overlap can induce significant changes in electronic coupling and electrical properties of organic devices and highlight the potential of charge transfer states as a disruptive approach to engineering organic electronics.