Michael Dürr

Tandem dye-sensitized solar cell for improved power conversion efficiencies

The power conversion efficiency of dye-sensitized solar cells crucially depends on the ability of the sensitizer to absorb light in a broad range of the solar spectrum. In order to increase this range of absorption, a tandem structure with two different sensitizer dyes in two different compartments of the cell, respectively, was realized. Overall power conversion efficiencies as high as η=10.5% and short circuit current densities of JSC=21.1 mA/cm2 were achieved under air mass 1.5 illumination with red dye and black dye in the upper and lower compartment of the cell, respectively.

On the origin of increased open circuit voltage of dye-sensitized solar cells using 4-tert-butyl pyridine as additive to the electrolyte

A combination of electrical measurements and surface analysis techniques was used to investigate the electronic structure of the TiO2/electrolyte interface and its change upon addition of 4-tert-butyl pyridine to the electrolyte. A reduced interface defect density and a resulting reduction of charge carrier recombination were found to be the main mechanism for an increased open circuit voltage of dye-sensitized solar cells with 4-tert-butyl pyridine in the electrolyte. The reduction of interface defect states was traced back to specific binding of 4-tert-butyl pyridine at defect sites on the TiO2 surface.A combination of electrical measurements and surface analysis techniques was used to investigate the electronic structure of the TiO2/electrolyte interface and its change upon addition of 4-tert-butyl pyridine to the electrolyte. A reduced interface defect density and a resulting reduction of charge carrier recombination were found to be the main mechanism for an increased open circuit voltage of dye-sensitized solar cells with 4-tert-butyl pyridine in the electrolyte. The reduction of interface defect states was traced back to specific binding of 4-tert-butyl pyridine at defect sites on the TiO2 surface.

Direct measurement of increased light intensity in optical waveguides coupled to a surface plasmon spectroscopy setup

The local increase of light intensity in waveguide structures was monitored by a combination of conventional surface plasmon spectroscopy and a dye-sensitized solar cell (DSSC). The sensitized nanoporous TiO2 layer of the DSSC served both as waveguide structure and light absorber in the DSSC. If the conditions for the excitation of guided modes in the TiO2 waveguide structure were fulfilled, increased light intensity in the porous layer was monitored by an increase of short circuit current in the DSSC. Comparison with direct illumination yields an increase of intensity by a factor of 19±6, in good agreement with transfer matrix calculations.