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SYOP: Symposium Organic Photovoltaics: From Single Molecules to Devices

SYOP 4: Organic Photovoltaics: from Single Molecules to Devices

SYOP 4.77: Poster

Donnerstag, 26. März 2009, 16:30–19:00, P1A

Morphology Control of Bulk-Heterojunction Solar Cells — •Hans W. A. Lademann, Yanyan Yuan, Adam J. Moulé, and Klaus Meerholz — Department Chemie, Universität zu Köln, Germany

The most studied solar cells are based on P3HT and PCBM. Several studies concentrate on influencing and optimizing the polymer:fullerene blend morphology as well as the determination of hole mobilities and conductivities in films made with different P3HT molecular weights via OFET measurements, but the exact impact of polymer aggregation on the resulting energy levels in the thin-film blend and the performance of solar cells is still not fully understood.

In this work, we investigated the influence of the degree of polymer aggregation on the energy levels in blends of P3HT and PCBM and the resulting solar cell performance. To achieve different degrees of P3HT aggregation in the thin films (i.e. different ratios of amorphous to aggregated P3HT) several preparation methods were investigated: 1) Two primary solvents with different boiling points, namely chlorobenzene and chloroform, were used for spin coating. 2) The role of an additional secondary solvent was investigated. 3) We studied the impact of the P3HT content in the polymer:fullerene blend and 4) changed the molecular weight of P3HT. As-cast as well as annealed films were investigated. AFM and UV/VIS spectroscopy were used to analyze the polymer aggregation. Kelvin Probe measurements were carried out to investigate the energy level in the thin films. Finally we compared the results obtained by these methods to the current-voltage characteristics of the solar cells, especially the Voc.