Abstract
The predictive accuracy of state–of–the–art continuum models for charge transport in organic semiconductors is highly dependent on the accurate tuning of a set of parameters whose values cannot be effectively estimated either by direct measurements or by first principles. Fitting the complete set of model parameters at once to experimental data requires to set up extremely complex multi–objective optimization problems whose solution is, on the one hand, overwhelmingly computationally expensive and, on the other, it provides no guarantee of the physical soundness of the value obtained for each individual parameter. In the present study we present a step–by–step procedure that enables to determine the most relevant model parameters, namely the density of states width, the carrier mobility and the injection barrier height, by fitting experimental data from a sequence of relatively simple and inexpensive measurements to suitably devised numerical simulations. At each step of the proposed procedure only one parameter value is sought for, thus highly simplifying the numerical fitting and enhancing its robustness, reliability and accuracy. As a case study we consider a prototypical n-type organic polymer. A very satisfactory fitting of experimental measurements is obtained, and physically meaningful values for the aforementioned parameters are extracted.
Highlights
Organic semiconductors are an outstanding candidate for becoming the material platform for the development of large–area, low cost, flexible electronics[1]
If a Density of States (DOS) consisting of a single Gaussian provides a reasonable fit, the carrier mobility can be predicted in the framework of the Extended Gaussian Disorder Model (EGDM)[6], and used to successfully fit the transfer characteristic curves of Organic Thin Film Transistors (OTFTs) in the linear regime
We find that the best fit to CV, CF and OTFT curves is obtained by assuming a Gaussian DOS width of 2.6 kBT and a barrier www.nature.com/scientificreports/
Summary
Organic semiconductors are an outstanding candidate for becoming the material platform for the development of large–area, low cost, flexible electronics[1]. The extraction of the DOS width requires the accurate knowledge of the device geometrical dimensions, of the insulator and semiconductor permittivities, of the total density of available states and, most notably, of the metal/semiconductor injection barrier (ΦB) between the bottom metal and the semiconductor The latter parameter is the one that suffers from the highest level of uncertainty: metal/semiconductor interfaces are still a subject of debate in the scientific community[7]; due to the various phenomena which may be involved (pillow effect, interface dipoles, charge transfer, chemisorption) the prediction of ΦB is a hard task, and its measurement requires very dedicated equipment such as XPS/UPS8 or Kelvin Probe[9,10,11]. The uncertainty is not negligible : by varying ΦB from 1 eV down to 0.5 eV, the DOS width reduces from about 3.5 kBT down to about 0.5 kBT, which appears to be a rather unphysical value
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