Significant progress in solution-processed organic thin film transistor (OTFT) over the last two decades has revealed a great promise in the domain of low-frequency flexible and rigid circuit applications. On the other hand, relatively less-studied organic metal-insulator-semiconductor capacitor (OMISCAP) device not only provides the basic understanding of OTFT in terms of field-driven switching from accumulation to depletion modes and vice- versa, but also be a prospective candidate for active/passive circuit applications. The array of OTFTs and OMISCAPs based on poly(2,5-bis(3-tetradecylthiophen-2yl)thieno[3,2-b]thiophene) (PBTTT-C14) as semiconductor and cross-linked poly(4-vinylphenol) (c-PVP) as polymer dielectric has been developed in our laboratory recently. This presentation will emaphasize on the controlling parameters enabling effective charge injection to improve the performance of OMISCAP and OTFT.

In the first part of the presentation, frequency dispersion of capacitance-voltage (C-V) characteristics of OMISCAP devices and the variation of cut-off frequency (fT) of capacitance dispersion upon varying the dielectric constant of the insulator and the hole injection barrier at the metal-semiconductor interface will be discussed. The second part of the talk will highlight the impact of contact engineering at the metal (source-drain)-semiconductor interface on the contact resistance of solution-processed bottom gate bottom contact (BGBC) OTFT. Considerable reduction of contact resistance upon lowering the thickness of the source-drain electrodes was further extended to realize OTFTs with recessed electrodes, embedded in the polymer gate dielectric for the first time. Planar substrate underneath the solution-processed organic semiconductor was found to reduce the contact resistance substantially with the overall performance improvement in terms of mobility, switch-on voltage and hysteresis. All the results related to OMISCAP and OTFT were further validated using TCAD simulation.