Built-in potential and validity of the Mott-Schottky analysis in organic bulk heterojunction solar cells

摘要

We investigated poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61 butyric acidmethyl ester bulk heterojunction (BHJ) solar cells by means of pulsedphotocurrent, temperature dependent current-voltage and capacitance-voltagemeasurements. We show that a direct transfer of Mott-Schottky (MS) analysisfrom inorganic devices to organic BHJ solar cells is not generally appropriateto determine the built-in potential, since the resulting potential depends onthe active layer thickness. Pulsed photocurrent measurements enabled us todirectly study the case of quasi flat bands (QFB) in the bulk of the solarcell. It is well below the built-in potential and differs by diffusion-inducedband-bending at the contacts. In contrast to MS analysis the correspondingpotential is independent on the active layer thickness and therefore a bettermeasure for flat band conditions in the bulk of a BHJ solar cell as compared toMS analysis.