Regensburg 2010 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 62: Poster II: Photovoltaics and Organic Semiconductors

HL 62.22: Poster

Donnerstag, 25. März 2010, 18:00–20:00, Poster D2

Charge transport in thin layers of nanocrystalline mesoporous Titania — •Steve Albrecht, Sylvia Paul, and Dieter Neher — Universität Potsdam, D-14476 Potsdam, Germany

Nanocrystalline mesoporous Titania (nc-TiO₂) has been shown to function as a very good electron acceptor in combination with common electron-donating polymers like poly(para-phenylene vinylene) or poly(3-hexylthiophene). However, charge transport in nc-TiO₂ layers is not well understood, though it might severely affect the energy conversion efficiency of those hybrid cells. Here, we present measurements of the electron mobility using the technique of charge extraction by linearly increasing voltage (CELIV). Layers of ca. 100 nm in thickness were prepared via dip-coating from a dispersion of 5 nm sized Titania particles. These layers were then annealed at different temperatures to remove the organic compounds. Unexpectedly, a pre-bias needed to be applied during the CELIV-measurements in order to obtain a measurable extraction peak. Apparently, those layers possess a high density of traps, which requires a certain number of electrons to be accumulated within the layer prior to the injection of mobile carriers. This interpretation was nicely confirmed by results from dark-injection measurements. We observed a significant increase of free carrier mobility with annealing temperature, reaching ca. 10⁻⁵ cm²/Vs for a layer annealed at 600^∘C, while the trap density decreased with temperature. In accordance to these results, the performance of hybrid solar cells improved largely when the nanocrystalline Titania layer was annealed at higher temperatures prior to the deposition of the polymers.