Photovoltaic and optoelectronic device group

Abstract:

The role of Schottky barrier at an electron-collection electrode in solid state dye-sensitized solar cells was investigated. A compact TiO2 layer was inserted between the fluorine-doped tin-oxide (FTO) anode and the nanoporous TiO2 in order to reduce loss through recombination between holes in the hole transporter and electrons in the FTO. An apparent positive shift in the conduction band was observed under UV illumination, which results in improving electron injection from the lowest unoccupied molecular orbital (LUMO) energy level of the dye molecules into the TiO2 conduction band, or into newly created states. It was demonstrates that a Schottky barrier exists at the FTO/TiO2 interface when a TiO2 compact layers is used between the FTO and the nanoporous film. Incorporation of an oxygen-rich compact layer in a solid state dye-sensitized solar cell is found to be improving the device performance.

Abstract:

A Li+ coordinating sensitizer, NaRu(4-carboxylic acid-4'-carboxylate)(4,4'-bis[(triethylene glycol methyl ether) methyl ether]-2,2'-bipyridine)(NCS)2 (coded as K51), has been synthesized, and the effect of Li+ coordination on its performance in mesoscopic titanium dioxide dye-sensitized solar cells has been investigated. Fourier transform infrared spectra suggest that Li+ coordinates to the triethylene oxide methyl ether side chains on the dye molecules. With the addition of Li+ to a nonvolatile liquid electrolyte, we observe a significant increase in the photocurrent density, with only a small decrease in the open-circuit voltage, contrary to a non ion coordinating dye which displays a large drop in potential with the addition of Li+. For a solar cell incorporating an organic hole-transporter, we find the potential rises with increasing the Li+ concentration in the hole-transporter matrix. For the liquid electrolyte and solid-state cells, we obtain power conversion efficiencies of 7.8% and 3.8%, respectively, under simulated sunlight.

Abstract:

We show that charge-transporting polymer chains in the brush conformation can be synthesized from a variety of substrates of interest, displaying a high degree of stretching and showing up to a 3 orders of magnitude increase in current density normal to the substrate as compared with a spin-coated film. These nanostructured polymeric films may prove to be suitable for electronic devices based on molecular semiconductors as current fabrication techniques often provide little control over film structure.

Abstract:

We present a new approach to achieving order in molecular semiconductors via alignment of polymer chains using surface-initiated polymerization. Polyacrylate brushes grown from transparent conducting electrodes, with triarylamine side groups as hole-transporting components, show characteristics of high mobilities for hole transport. Solution processing a second component with favorable enthalpic interactions can form a composite with mesoscale order and be exploited for heterojunction diodes. We find substantial uptake of CdSe nanocrystals (with diameter in the range 2.5-2.8 nm), and such composites show photovoltaic quantum efficiencies of up to 50%.