AVS 61st International Symposium & Exhibition
    Energy Frontiers Focus Topic Monday Sessions
       Session EN+EM+MN+NS+TR-MoA

Paper EN+EM+MN+NS+TR-MoA10
Doped TiO2 Based Core-Shell Structures for High Efficiency Hybrid Solar Cells

Monday, November 10, 2014, 5:00 pm, Room 315

Session: Energy Harvesting with Nanostructures
Presenter: Jonas Weickert, University of Konstanz, Germany
Authors: J. Weickert, University of Konstanz, Germany
J. Dorman, University of Konstanz, Germany
M. Noebels, University of Konstanz, Germany
M. Putnik, University of Konstanz, Germany
T. Pfadler, University of Konstanz, Germany
A. Wisnet, LMU Munich, Germany
C. Scheu, LMU Munich, Germany
L. Schmidt-Mende, University of Konstanz, Germany
Correspondent: Click to Email
Hybrid solar cells, with an inorganic/organic interface for charge separation, have been extensively investigated in the past decade in order to replace the expensive Si based technology with an inexpensive alternative. Typically, these devices incorporate a mesoporous TiO2 film which is decorated with dye molecules and filled with a hole transport polymer, for example P3HT, to conduct the electrons and holes, respectively. Recently, we have shown that the efficiency of nanowire based hybrid solar cells can be increased from ~1.8 % to 2.5 % through the formation of a Sn-doped TiO2|TiO2 core-shell device created via a hydrothermal growth and subsequent TiCl4 treatment. However, this surface treatment presents difficulties in creating a crystalline conformal coating, limiting the control over the extent of coating and the crystallinity, directly affecting the charge injection from the polymer into the TiO2 array. In this work, we directly deposit a controllable TiO2 film through atomic layer deposition to conformally coat the nanowire arrays with various thicknesses. By changing the thickness and TiO2 crystallinity, we are able to engineer the energy levels at the TiO2-dye-P3HT interface due to the magnitude and position of the Fermi levels of the core and shell material, influencing the rate of charge injection and recombination. Furthermore, the crystallinity of the shell layer directly affects the amount of dye that can be absorbed on the surface of the nanostructures with a reduction in light absorption by roughly 30% from anatase to rutile TiO2. Finally, a detailed mechanism will be proposed for the device performances based on the energy level alignment between the pinned Fermi-level TiO2 structure and the HOMO of the P3HT resulting in a shifting open circuit voltage based on the crystal phases. Additionally, the core-shell structures are characterized with photovoltage decay and impedance spectroscopy measurements to study the charge transport and recombination across these various interfaces.