Browsing by Author "Podzorov, V."
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Item Charge Carrier Coherence and Hall Effect in Organic Semiconductors(Nature Publishing Group, 2016-03-30) Yi, H. T.; Gartstein, Yuri N.; Podzorov, V.; Gartstein, Yuri N.Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.Item Stable Doping of Carbon Nanotubes via Molecular Self Assembly(2014-10-13) Lee, B.; Chen, Y.; Cook, Alex; Zakhidov, Anvar A.; Podzorov, V.; 0000 0003 5287 0481 (Zakhidov, AA); Zakhidov, Anvar A.We report a novel method for stable doping of carbon nanotubes (CNT) based on methods of molecular self assembly. A conformal growth of a self-assembled monolayer of fluoroalkyl tri-chloro-silane (FTS) at CNT surfaces results in a strong increase of the sheet conductivity of CNT electrodes by 60-300%, depending on the CNT chirality and composition. The charge carrier mobility of undoped partially aligned CNT films was independently estimated in a field-effect transistor geometry (~100 cm² V⁻¹ s⁻¹). The hole density induced by the FTS monolayer in CNT sheets is estimated to be similar to 1.8 x 10¹⁴ cm⁻². We also show that FTS doping of CNT anodes greatly improves the performance of organic solar cells. This large and stable doping effect, easily achieved in large area samples, makes this approach very attractive for applications of CNTs in transparent and flexible electronics.