Investigation of Excitonic Gates in Organic Semiconductor Thin Films

We demonstrate that interfaces can play a significant role in overcoming the diffusive and subdiffusive nature of exciton transport in organic semiconductors. By designing interfaces with an imbalance between the forward and reverse rates of energy transfer, the interface can act as a gate, thereby directing exciton transport. While previous work has examined from a theoretical perspective the function of multiple exciton gates arranged in series, we provide a combined theory-experiment treatment that permits an assessment of the utility of exciton-permeable gating interfaces in optoelectronic devices. The required asymmetry in interfacial-exciton-transfer rates is realized by engineering a molecular site imbalance. The impact of interfaces on exciton transport is considered by optically injecting excitons into the gating architecture, and detecting those that migrate through the structure using a luminescent sensitizer. For exciton transport in the archetypical organic fluorescent dye 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10(2-benzothiazolyl) quinolizino-[9,9a,1gh] coumarin (C545T) diluted in the wide-gap organic semiconductor p-bis(triphenylsilyl)benzene (UGH2), a more than 200% improvement in transport efficiency is found in an architecture with properly optimized gates compared to a neat film of C545T.