3.3 Investigating Charge Transport in Organic Semiconductors with Electrochemical Methods and Modelling

Today organic semiconductors are used in many technological applications. However, these materials must be thoroughly studied in order to design even better products. Our project aims to improve the characterization of organic semiconductors using electrochemical measurements in combination with computer simulations.

Contributors: Partner(s): Funding: Duration: G. Kissling, E. Knapp, K. Pernstich Fluxim Swiss National Science Foundation (SNSF) 2020–2022

Nowadays organic semiconductors are widely used in display and lighting applications (OLED TVs and light panels) and also in the fabrication of novel transistors, sensors, data storage elements and solar cells. In order to produce better devices, the understanding of the physical processes and the materials properties of organic semiconductors needs to be improved. In this interdisciplinary project we investigate organic semiconductor materials using electrochemical methods and (theoretical) multiphysics modelling. The project combines the ICP department’s computer modelling-expertise with fundamental electrochemistry research. The aim of the project is the development of a reliable method for the characterization of a range of organic semiconductor properties and materials parameters. The experiments will give us insight into some properties which have so far been very hard or almost impossible to measure. The data will be fed into a detailed theoretical model. Common numerical models can then be optimized using our experimental results. We are using electrochemical methods to characterize organic semiconductors, such as NPB (N,N′di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′diamine), shown in Figure 1c. NPB will either be studied as a molecule in solution or as a thin film adsorbed onto a substrate. The stability and the semiconductor properties (such as the positions of the valence and conduction band and of defect states) of the material will be investigated. Figure 1a and b show preliminary electrochemical data simulated for NPB in solution obtained using COMSOL Multiphysics® software [1]. The red part of the trace in Fig. 1a was simulated using experimentally determined parameters from the literature [2]. The blue part and the electrochemical impedance spectra in Fig. 1b are based on an educated guess and will be confirmed or rejected by our own experimental results over the coming year. This project may lead to an improved understanding of the current state of the art by providing inputs that lead to the development of more accurate models for organic semiconductor materials characterization. In collaboration with our industrial partners the research may also lead to the development of a commercial product.

Fig. 1: a First Simulated cyclic voltammograms for NPB in solution. The red data were simulated using experimental results from the literature [2]. The blue data are based on an educated guess. The electrochemical impedance spectra in b were simulated for the potentials indicated in a. The spectra were simulated for potentials of -1 V (orange circle), 0.46 V (dark green triangle), 0.5 V (purple square) and 0.54 V (blue pentagon). c cartoon representation of an NPB molecule.

Literature:

[1] COMSOL Multiphysics® v. 5.5. www.comsol.com. COMSOL AB, Stockholm, Sweden. [2] J.-E. Park, S. Song and I.-S. Shin, Int. J. Electrochem. Sci., 2016, 11, 5891–5899.