Organic Thin-Film-Transistors (otfts) are being studied as (i) replacement for a-Si:H tfts in amoleds backplanes, (ii) sensor (chemical, physical and biological), and (iii) component for electronic circuits. The understanding and possibly engineering of charge carrier transport is crucial in optimizing device performance. In this work, charge concentration-dependent carrier mobility is used as a tool to study the effect of Pentacene polymorphs on the electrical properties of Pentacene otfts. In the first part of the work, various device fabrication techniques and methods to extract electrical parameters from device response are discussed. The fabrication process is optimized systematically to develop Pentacene transistors with greatly diminished non-idealities. A new approach to estimate gate bias-dependent mobility is proposed.

In organic semiconductors, charge carrier transport is by carrier hopping along a manifold of discrete electronic states, which constitutes the density of states (DOS). In the second part of the work, an effective method to estimate the width (s) of the DOS of the Highest Occupied Molecular Orbital (HOMO) in Pentacene using field-effect studies is presented. This method is further employed to understand the charge transport in Pentacene otfts with different morphology of the film in the channel. It is shown that the hole mobility primarily depends on the crystalline phases of the thin film rather than on the crystalline grain size. The presence of different crystalline phases and their effect on carrier mobility and disorder is discussed.