Molecular and Organic Nano-electronics

Organic electronics is currently experiencing a surge of activities worldwide prompted in part by recent advances in achieving high electronic mobility, light emission over a broad range of frequencies, demonstration of spin valve operation with giant magneto-resistance and other effects. Despite these encouraging premises, there are many roadblocks that hinder a broader proliferation of plastic electronics in contemporary technology. Arguably, the most significant of them is the challenge to achieve a comprehensive understanding of the fundamentals of charge injection and charge transport in polymers and in organic molecular crystals.

Recent Results:

Infrared spectroscopy and imaging of ambipolar donor-acceptor polymer transistors
Khatib et al. PRB 90, 235307 (2014). Article [201]

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picture111The donor-acceptor (DA) approach to synthesizing polymers has led to a new generation of high-mobility ambipolar systems, a necessary precondition for many transistor, photovoltaic, and light-emitting device applications. Despite much recent progress, however, there remains an incomplete understanding of the fundamental nature of charge transport and dynamics, especially in DA systems that accommodate both types of carriers. Here we use an IR microscope to probe the spectroscopic signatures of electron and hole injection in the conduction channel of an organic field-effect transistor based on an ambipolar DA polymer. We observe distinct polaronic absorptions for both electrons and holes and spatially map the carrier distribution from the source to drain electrodes.

 

Light quasiparticles dominate electronic transport in molecular Crystal FETs
Li et al. Physical Review Letters 99, 016403 (2007). Article [111]

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picture112We report on an infrared spectroscopy study of mobile holes in the accumulation layer of organic field-effect transistors based on rubrene single crystals. Our data indicate that both transport and infrared properties of these transistors at room temperature are governed by light quasiparticles in molecular orbital bands with the effective masses m? comparable to free electron mass. Furthermore, the m? values inferred from our experiments are in agreement with those determined from band structure calculations. These findings reveal no evidence for prominent polaronic effects, which is at variance with the common beliefs of polaron formation in molecular solids.