Charge Transport Investigation in Solution Processed Organic Field-Effect Transistors Based on sp-Hybridized Cumulenic Carbon Wires

High-mobility organic semiconductors are the key to develop performant devices for large-area flexible electronics applications. Traditionally, organic semiconductors are π-conjugated polymers and small molecules with a molecular structure based on sp²-hybridized carbons. This peculiarity is also common to carbon nanostructures, like graphene, carbon nanotubes and fullerenes, which have been widely explored towards opto-electronic applications.<br/>In this talk, we report on the potential of sp-hybridized cumulenic carbon atom wires as a novel class of solution processable molecular semiconductors for organic electronics. Carbon atom wires are linear chains of sp-hybridized carbon atoms and represent the ultimate one-dimensional allotropic form of carbon. ^[1]They exhibit two possible isomeric configurations: cumulenes (sequence of double bonds) and polyynes (sequence of single and triple alternated bonds). Theoretical studies have predicted outstanding mechanical, optical and electronical properties for these structures. However, only a few experimental studies have investigated their electronic properties in solid-state devices and, so far, they have focused mainly on molecular junctions or monolayers. ^[2]Recently, we have demonstrated the first example of organic field-effect-transistor (OFET) based on short cumulenic molecules, namely tetraphenylbutatriene ([3]Ph). ^[3]Herein, we discuss on our latest achievements in understanding and optimizing charge-transport properties in solution processed thin-films of [3]Ph, deposited by a scalable large-area wire-bar coating technique. Our [3]Ph based OFETs display ideal characteristics and reliable field-effect-mobilities exceeding 0.1 cm²V^-¹s^-¹. Moreover, in dark conditions, they provide excellent operational stability in air, thus addressing one of the greatest concerns for employing sp-systems in concrete applications.<br/>Finally, we unveil by Raman and Charge Modulation Spectroscopy (CMS) the peculiar charge transport features of these sp-based semiconductors. CMS allows to directly probe the spectral features induced by a periodic modulation of the charge density in the transistor channel, providing information on the transport of mobile charges in the device working conditions. ^[4]<br/>These results hold promise for the exploitation of a new library of molecular semiconductors based on sp-hybridized conjugated systems.<br/><br/>[1] C. S. Casari, M. Tommasini, R. R. Tykwinski and A. Milani, Nanoscale 2016.<br/>[2] M. R. Bryce, J. Mater. Chem. C 2021<br/>[3] A. D. Scaccabarozzi, A. Milani, S. Peggiani, S. Pecorario, B. Sun, R. R. Tykwinski, M. Caironi, and C. S. Casari, J. Phys. Chem. Lett. 2020.<br/>[4] Meneau, A.Y.B., Olivier, Y., Backlund, T., James, M., Breiby, D.W., Andreasen, J.W. and Sirringhaus, H., Adv. Funct. Mater. (2016).