Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 6: Poster: Structural Ordering and Electronic Transport (joint focus with HL)

CPP 6.29: Poster

Monday, March 26, 2012, 17:30–19:30, Poster A

Built-in potential and validity of Mott-Schottky analysis in organic bulk heterojunction solar cells — •Markus Mingebach¹, Carsten Deibel¹, and Vladimir Dyakonov^1,2 — ¹Experimental Physics VI, Julius Maximilian University of Würzburg, D-97074 Würzburg — ²ZAE Bayern, D-97074 Würzburg

The built-in potential is an important key parameter of organic bulk heterojunction (BHJ) solar cells since it determines the internal electric field profile in the device but also gives an estimate for the open circuit voltage and hence the solar cell efficiency. The correct determination of the built-in potential is a nontrivial task, since zero field inside the BHJ device is not easy to achieve. We investigated poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61 butyric acid methyl ester BHJ solar cells by means of temperature dependent measurements of the open circuit voltage and compared the results with the Mott-Schottky analysis of capacitance-voltage characteristics, which is a well-established tool to determine the built-in potential in inorganic devices. By applying the Mott-Schottky analysis to our solar cells we found considerably lower built-in voltages than expected from the difference of the electrode work functions. Moreover, a dependence of the built-in voltage, determined this way, on the active layer thickness of the devices was observed. We conclude that Mott-Schottky analysis seems not to be generally appropriate for the determination of the built-in potential in organic BHJ solar cells.