Small-molecule organic semiconductors form the basis for the emerging field of organic optoelectronics. In order to better understand the intrinsic photo-physical and transport phenomena in this important class of materials, it is necessary to study samples of very high structural order and chemical purity. Such materials exist in the form of molecular single crystals that can be used for fabrication of high-performance prototype devices, such as field-effect transistors, photo-conductors and photo-voltaic cells, in which intrinsic properties of organic semiconductors can be investigated without parasitic effects of disorder (see, e.g., [1,2,3]). This talk will overview some of the main achievements in the area of organic single-crystal devices, present resent progress and discuss novel methods of surface functionalization that result in an extremely low-noise charge transport regime at the surface of molecular crystals, leading to an observation of unprecedentedly clean and quiet (low-noise) Hall effect [4].  In addition, very interesting non-linear effects in photoconductivity originated from long-range exciton diffusion and multi-particle interactions will be discussed [5].     

References:

1. V. Podzorov, MRS Bulletin themed Issue: “Organic Single Crystals: Addressing fundamentals

   of organic electronics” introductory paper, MRS Bulletin 38, 15-24 (Jan. 2013).

2. V. Podzorov et al., "Hall effect in the accumulation layers on the surface of organic

    semiconductors", Phys. Rev. Lett. 95, 226601 (2005).

3. H. Najafov, B. Lee, Q. Zhou, L. C. Feldman, V. Podzorov, "Observation of long-range exciton

    diffusion in highly ordered organic semiconductors", Nature Mater. 9, 938 (2010).

4.  B. Lee, Y. Chen, D. Fu, H. T. Yi, K. Czelen, H. Najafov, V. Podzorov, “Trap healing and

     ultra low-noise Hall effect at the surface of organic semiconductors”, Nature Mater. 12, 1125

     (2013).

5. P. Irkhin, H. Najafov, V. Podzorov, submitted (2014).