Interface Engineering for Photovoltaics
[Jonathan Bakke, Thomas Brennan]

Dye-Sensitized Solar Cells
Dye-sensitized solar cells (DSSCs) represent a promising photovoltaic technology. The original design includes a monolayer of organic or ruthenium-based dyes adsorbed on a high-porosity TiO₂ substrate (the electron transporter) surrounded by an iodine electrolyte solution (the hole conductor). It is desirable to replace the liquid electrolyte with a solid state hole conductor in order to improve device stability, but such solid state DSSCs have yet to reach the efficiencies attained by liquid cells. This is due primarily to electron-hole recombination, which occurs much more readily in the solid state design. Our research focuses on engineering the dye-TiO₂ interface using both organic and inorganic modifiers in order to reduce recombination and improve efficiency. The resultant systems are characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-Vis absorption spectroscopy, and synchrotron methods, and by solar cell testing techniques including photoluminescence quenching and current-voltage measurements.

Schematic of a solid-state dye-sensitized solar cell

CIGS Interface Engineering
Copper indium gallium diselenide (CIGS) is one of the most promising absorber technologies for thin film photovoltaics, and variations on CIGS solar cells are currently being manufactured by several solar cell companies. Sunlight is absorbed in the CIGS layer, and the charge is extracted and transported through the buffer layer before being collected by the electrodes. The most promising buffer layer is a very thin layer of cadmium sulfide deposited via chemical bath deposition; however, due to health concerns involved with cadmium, other materials are being studied for buffer layers, and ALD is one most promising alternatives for depositing these thin layers of n-type semiconductors. We are currently looking at new materials and methods for the buffer layer deposition in CIGS photovoltaics via ALD.