(472b) Characterization of Recombination Barrier Layers in Dye-Sensitized Solar Cells | AIChE

(472b) Characterization of Recombination Barrier Layers in Dye-Sensitized Solar Cells

Authors 

Brennan, T. P. - Presenter, Stanford University
Bakke, J. R. - Presenter, Stanford University
Mondal, R. - Presenter, Stanford University
Bent, S. - Presenter, Stanford University
Miller, C. E. - Presenter, Stanford Synchrotron Radiation Laboratory
Nordlund, D. - Presenter, Stanford Synchrotron Radiation Laboratory
Toney, M. F. - Presenter, Stanford Synchrotron Radiation Laboratory


 Research interest in solar energy due to
climate and energy security concerns has resulted in many photovoltaic
technologies.  One such example is the dye-sensitized solar cell (DSSC) which
employs a monolayer of ruthenium-organic dye molecules adsorbed onto a TiO2
substrate as the photon absorber. The original DSSC design in which an iodine
electrolyte solution regenerates the oxidized dye has achieved efficiencies in
excess of 12%.  More practical solid-state devices, however, have only achieved
efficiencies of ~6% due to the higher rate of charge recombination between
electrons in the TiO2 and holes in the solid-state hole conductor,
Spiro OMeTAD.  One way to slow this recombination route is to add an insulating
layer between the TiO2 and the dye layer.  The insulating layer can
be either organic (e.g. a self-assembled monolayer) or inorganic (e.g. metal
oxide) but charge injection considerations restrict layer thickness to
approximately 1 nm.  Barrier layers under study in this work include amine-terminated
phosphonic acids and metal oxides such as Al2O3 and ZrO2
In addition to the dielectric properties of such an insulating layer, the
conformation of the dye layer at the bare or coated TiO2 substrate
will also affect device performance.  To determine the dye conformation, smooth
TiO2 substrates were grown via atomic layer deposition, and adsorbed
dye layers were studied on these TiO2 films?both bare and with barrier
layers?by X-ray reflectivity (XRR) and near edge X-ray absorption fine
structure (NEXAFS) spectroscopy.  Using angle-resolved NEXAFS, we have
elucidated the orientation of the recently-developed YE05 dye and the more
common Z907 dye on bare TiO2 and on barrier layers.  XRR provides
insight into the dye and barrier layers' densities and thicknesses and confirms
the deposition of a monolayer.  Solid-state DSSCs have also been fabricated and
tested using conventional high-porosity TiO2 substrates.  By coupling
the structural characterization of the well-defined surfaces with real device
performance, the effect of dye orientation and barrier layers on device
performance in solid-state DSSCs can be better understood.