Contatto di riferimento: Beatrice Fraboni
Partecipanti: Dr.Riccardo Di Pietro: Hitachi Cambridge Laboratory, CB3 0HE Cambridge, United Kingdom
Abstract
The recent development of high mobility polymer semiconductors has led to measurements, such as the observation of Hall conductivity and the thermoelectric effect, that question our understanding of charge transport in organic semiconductors.1,2
In this talk I will focus on the characterisation of field effect transistors fabricated with well-known semiconducting polymers, poly{[N,N′-bis(2-octyl-dodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)) and poly(3-hexylthiophene) (P3HT).3
We experimentally observe an increase in the charge density dependence of the mobility connected with an overall improvement of device performance. We unambiguously correlate such effect to the increase of the average crystallite size in the semiconducting polymer film by combining the results of optical spectroscopy and X-ray characterization. The picture that emerges from the experimental evidence conclusively demonstrates that charge transport in semicrystalline polymers is not dominated by disorder and therefore cannot be described using any disorder based model such as multiple trap and release or variable range hopping.
To explain these experimental observations, we propose a model that explicitly accounts for the presence of interspersed crystalline and amorphous regions within the polymer film and for the Coulomb interaction between charge carriers accumulated within the same crystallite. With this approach, we can provide a coherent picture of charge transport that captures all the unique features observed experimentally.
1Venkateshvaran, D. et al. (2014), Approaching disorder-free transport in high-mobility conjugated polymers, Nature, 515, 348, doi:10.1038/nature13854.
2Kang, S. D. and Snyder, G. J. (2016), Charge-transport model for conducting polymers, Nature Materials, 16, 252, doi:10.1038/nmat4784
3Di Pietro, R. et al. (2016), Coulomb Enhanced Charge Transport in Semicrystalline Polymer Semiconductors. Adv. Funct. Mater., 26, 8011, doi:10.1002/adfm.201602080.
Short biography
I studied Physics at the University of Bologna where I graduated in 2006 with a thesis on the electrical characterisation of thiophene derivatives under the supervision of Prof. Beatrice Fraboni. After a brief stint as process engineer in a solar cell production factory in Padova, I did a PhD in the group of Prof. Sirringhaus at the university of Cambridge where I developed a technique for the optical detection of trap and mobile electronic states in polymer semiconductors. In 2012 I moved to the University of Potsdam working on charge transport in semicrystalline polymer semiconductors in the group of Prof. Dieter Neher. I am currently a research scientist at the Hitachi Cambridge Laboratory, focusing on the charge and spin transport physics of organic semiconductors.