Dresden 2006 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
HL: Halbleiterphysik
HL 32: Photovoltaic
HL 32.7: Vortrag
Mittwoch, 29. März 2006, 16:00–16:15, BEY 118
Efficiency limitations in dye-sensitized solar cells with ionic liquids — •F. Einsele1, M. Hlusiak1, U. Rau1, R. Sastrawan2, R. Kern2, and A. Hinsch2 — 1Institut für Physikalische Elektronik, Universität Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart — 2Fraunhofer Institut für Solare Energiesystem (ISE), Heidenhofstraße 2, 79110 Freiburg
Dye-sensitized solar cells (DSCs) consist of a layer of nanoporous TiO2. A monolayer of dye molecules covers the TiO2 nanoparticles. Photoexcitation of the dye and electron transfer into the conduction band of the TiO2 makes up the primary photovoltaic action. The I−/I3− redox couple of an electrolyte (EL) oxidizes the dye molecule. Standard high-efficiency DSCs use an EL with highly volatile acetonitrile as a solvent. One major research goal is the replacement of this EL by a non-volatile EL. Here the use of ionic liquids is a major option. Unfortunately, the efficiencies, especially the short circuit current densities jSC, obtained with these EL so far are much lower than those of the standard devices. The present contribution investigates possible limitations to jSC by means of electrical measurements. We find that the diffusion constant DT of I3− in ionic liquids is 1.8x10−7 cm2/s, i.e. about two orders of magnitude smaller than 1.2x10−5 cm2/s in acetonitrile. A further limitation is provided by the TiO2 network and in an additional light-scattering ZrO2 layer. We observe that the effective diffusion constant Deff in the TiO2 network is about 40% of the bulk value and reduces to 16% in the ZnO2 layer. A simple model unveils that the maximum achievable short circuit current density jSC,max is about 8 to 10 mA/cm2 in this case.