Berlin 2015 – scientific programme
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DS: Fachverband Dünne Schichten
DS 7: Organic photovoltaics and electronics - mostly properties of the absorber (jointly with CPP,DS)
DS 7.3: Talk
Monday, March 16, 2015, 17:30–17:45, EW 202
New Insights on traps states in organic semiconductor devices using transient current measurements on metal-insulator-semiconductor capacitors — Hippolyte Hirwa and •Veit Wagner — Jacobs University, Bremen, Germany
A Transient current measurement technique utilizing metal-insulator-semiconductor (MIS) capacitors is developed, which does not need a light stimulus. The technique offers insights on carrier trapping states such as capture time of trapping states and the attempt-to-escape frequency of trapped carriers. For the analysis of the measurements Fourier transformation of imepdance-based circuit models to the time domain as well as direct numerical simulation of transient current of MIS capacitors were used. Numerical simulations allow to go beyond the usual assumptions of negligable extraction time for de-trapped carriers. It is shown, that re-trapping events are relevant in order to extract the proper band tail density of states and the corresponding characteristic parameters. For e.g. P3HT an exponential density of states with a total density of 4· 1017 cm3 and a width of 50 meV was found to be representative for the band tail. Analyzing the multiple trap and release behavior in the numerical simulation, the average capture time and the attempt-to-escape frequency of band tail states were found to be 10−10 s and 108 s−1, respectively.