Because most organic semiconductors are disordered, the more appropriate function to describe their density of states (DOS) is the Gaussian distribution. A striking difference between the Gaussian DOS and the parabolic DOS found in conventional inorganic semiconductors is the fact that it does not allow for a simple and straightforward definition of the band edge. The most usual way found in the literature to define the band edge of a Gaussian DOS consists of extrapolating the tangent to the inflection point of the Gaussian curve. The aim of this paper is to discuss the validity of such a way of conduct. An analysis of data found in the literature shows that the width of the Gaussian distribution is significantly larger than what usually retained in transport models. It is also shown that the validity of the usual definition for the band edge is questioned by the fact that the density of charge carriers behave as a degenerate distribution, even at relatively low doping levels.

This paper reports on the sensing of proteins using water-gated organic field-effect transistors. As a proof-of-concept, streptavidin and avidin were used, with a biotinylated polymer as the active sensing material. The latter is a copolythiophene modified to graft biotin by peptidic coupling. After characterization of its structure, it was integrated as the channel material into transistors and its interactions with several proteins were investigated. Non-specific interactions were reduced when the polymer surface was pretreated with 1-octanol. In this case, human serum albumin had no effect on the transistor characteristics whereas avidin and streptavidin led to a decrease of the drain current.

We present a drain current model and a consistent parameter extraction method for organic field-effect transistors (OFETs) considering the gate voltage-dependent contact resistance and mobility by power-law. The physical origin of the asymptotic power-law dependence of contact resistance is elaborated based on the current crowding model. The parameters of a new model can be completely extracted without ambiguity by the proposed extraction method based on the linear fitting. Pentacene-based OFETs with the Au source/drain contact in a staggered configuration experimentally validate the proposed model and the extraction method, which further reveal the bulk resistivity as the major contribution to contact resistance.

We develop a numerical model for the current-voltage characteristics of organic electrochemical transistors (OECTs) based on steady-state Poisson’s, Nernst’s and Nernst–Planck’s equations. The model starts with the doping–dedoping process depicted as a moving front, when the process at the electrolyte–polymer interface and gradually moves across the film. When the polymer reaches its final state, the electrical potential and charge density profiles largely depend on the way the cations behave during the process. One case is when cations are trapped at the polymer site where dedoping occurs. In this case, the moving front stops at a point that depends on the applied voltage; the higher the voltage, the closer the stopping point to the source electrode. Alternatively, when the cations are assumed to move freely in the polymer, the moving front eventually reaches the source electrode in all cases. In this second case, cations tend to accumulate near the source electrode, and most of the polymer is uniformly doped. The variation of the conductivity of the polymer film is then calculated by integrating the density of holes all over the film. Output and transfer curves of the OECT are obtained by integrating the gate voltage-dependent conductivity from source to drain.

In this review, recent advances in compact modeling of organic field-effect transistors (OFETs) are presented. Despite the inherent strength for printed flexible electronics and the extremely aggressive research conducted over more than three decades, the OFET technology still seems to remain at a relatively low technological readiness level. Among various possible reasons for that, the lack of a standard compact model, which effectively bridges the device-and system-level development, is clearly one of the most critical issues. This paper broadly discusses the essential requirements, up-to-date progresses, and imminent challenges for the OFET compact device modeling toward a universal, physically valid, and applicable description of this fast-developing technology.

Correct parameterization of the Gaussian disorder model (GDM) on spatially random sites is necessary for a complete description of charge transport in disordered materials and concomitant device characteristics. Because the GDM on spatially random sites considers both energetic and spatial disorder, it is superior to the GDM on a cubic lattice. However, analytical arguments and experimental evidence are still lacking for correct parameterization of the model over a wide range of model parameters, energetic and spatial disorder, and electric fields. We show that the model requires a set of parameters to correctly account for high mobility and its charge density dependence, and we develop such a model. The model is implemented in a numerical simulation tool for comparison with the measured device characteristics. Accurate agreement with experimental data, particularly with the high mobility values in organic field-effect transistors, is achieved throughout a wide range of temperature by adjusting both the localization length and the attempt-to-escape frequency.