Photovoltaic & Optoelectronic Device Group

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%.