Regensburg 2010 – scientific programme
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DS: Fachverband Dünne Schichten
DS 26: [CPP] Organic Electronics and Photovoltaics III (Joint Session DS/CPP/HL/O)
DS 26.7: Talk
Wednesday, March 24, 2010, 11:15–11:30, H37
Thickness dependent structural order in P3HT films - a key parameter for high OFET mobility — •Benedikt Gburek, Richa Sharma, Torsten Balster, and Veit Wagner — School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
Applications of organic electronics require cheap and fast production methods on flexible substrates. Following these goals, top-gate OFETs on PET foils were used to analyze the dependence of the device characteristics on the crucial parameter of semiconductor layer thickness. The organic semiconductor, regio-regular P3HT, and the gate insulator were deposited by spin-coating under atmospheric conditions.
The charge carrier mobility was found to be rather low for extremely thin layers of several nanometers only. However, with increasing layer thickness, mobility increases by two orders of magnitude until a "saturation thickness" of 50 nm, above which it remains constant.
Further details of the ordering were extracted according to the Vissenberg-Matters model with gate-voltage dependent mobility µ = µ0 ((VGS − Vth) / 1 V)γ, where γ is directly related to the width of the density of states. The analysis reveals that the disorder parameter γ decreases from 3.1 to 1.0 over the examined thickness range, which explains the low mobility of thinner films by higher energetic disorder.
This analysis proves to be highly advantageous as it represents the whole transfer curve, gives better comparability and offers more physical insight. Our study demonstrates the crucial role of layer thickness tuning for improved film structure and optimum material performance.