Lignin structural, chemical and physical characterization and dielectric performance in organic field-effect transistors

An organic field-effect transistor (OFET) is a field-effect transistor that uses semiconductive properties of organic materials. Dielectrics and semiconductors are the inner constituents of OFETs, mostly responsible for the success of the technology. The emerging necessity for safe, non-toxic, and ecologically sustainable organic electronics and bioelectronics, in opposition to the less sustainable inorganic counterparts, requires the use of green functional materials1 . In this perspective, we studied the use of lignin as dielectric layer in OFETs. Lignin is an abundant biopolymer synthesized by plants and a waste of diverse pulping processes. Lignin is rich in aromatic ring content. Its use in materials science is limited by the scarce knowledge on its structure, which depends also on its isolation method. In this work, we analyse the structural and chemical-physical characteristics of two commercially available kraft lignins, named L1 and L2, deriving from softwood by the kraft process, differing for the isolation process (acid or alkaline). First, we apply several molecular characterization techniques, such as ATR-FTIR, elemental analyses, GPC-HPLC, EGA MS, UV-Vis, 31P- and 13C-NMR spectroscopies to get insights into their different structures and their degree of molecular degradation, then we fractionate the two lignins to investigate the effects of solvent fractionation on the chemical structures and the impact of two different methods such as Soxhlet and Kumagawa extraction2 . Finally, we demonstrate their efficient application as gate dielectric in bottom-gate top-contacts organic field effect transistor (OFET) devices and how structural characteristics will affect their efficiency as gate dielectric polymer