PHOTOVOLTAIC AND INTERFACIAL PROPERTIES OF HETEROJUNCTIONS COMPRISING DYE-SENSITIZED DENSE TiO2 AND TRIARYLAMINE DERIVATIVES IN SOLID AND LIQUID STATE.

• Different triarylamine derivatives have successfully been used as solid hole-conductor materials in dye-sensitized solar cells with efficiencies up to 4% [1-3]. In the present work TiO2/dye/ hole-conductor heterojunctions is assembled to form model systems for solid state DSSC and the interfacial structure at the molecular level. A series of triarylamine molecules is used to investigate the influence of small differences in the hole-conductor material structure on the photovoltaic and molecular surface properties. Both solid state and liquid state junctions with the triarylamine molecules were investigated. In the solid state heterojunctions the hole-conductor molecules were evaporated on the substrate and in the liquid state heterojunctions the hole-conductor molecules were solvated in an organic solvent. The photovoltaic properties of the heterojunction largely depend on the electron transfer rates at the interfaces between the different materials (semiconductor, dye and hole-conductor). Photoelectron Spectroscopy (PES) measurements was used to investigate the molecular and electronic interface structure. In the figure below the valence electronic structure of interfaces with the different hole-conductors are shown.From the valence PES the interaction and the energy level matching between the dyes and the hole-conductors is studied. The results show large differences in the energy matching of the different holconducting materials with respect to the dye molecules partly explaining the differences in efficiency. The valence structure also shows that when combining different materials their individual properties adjust slightly to their new environment. From the core level PES we observe differences molecular surface structure. Specifically it was found that the smaller holecondctors are able to penetrate the dye layer and contact the TiO2 surface.

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