A new way of anchoring dyes in organic solar cells improves their performance, say an international team of scientists.

The anchor is separated from the acceptor so the donor and acceptor can be easily modified

Dye-sensitised solar cells (DSCs) contain an organic dye that releases electrons when excited by sunlight. The electrons are transferred to a semiconductor to generate electricity. The dye consists of a donor unit and an acceptor unit separated by a spacer group. Most DSCs use cyanoacrylic acid coupled to the acceptor unit to anchor the dye to the semiconductor. However, this makes it difficult to modify the dye's structure to improve the cell's performance.

Xichuan Yang, at Dalian University of Technology, China, and colleagues changed the anchoring group to propanoic acid and attached it as a lateral chain to the donor unit. By separating the anchor from the acceptor, the team could easily modify the donor and acceptor units' structures to tune the dye's absorption spectra. Their new dyes were better at absorbing near infrared light than previously reported dyes of this type and so were more efficient at converting sunlight to electricity.

'This strategic change opens up possibilities for the design and synthesis of a new generation of organic dyes with broad absorption spectra and high molar extinction coefficients,' comments Yang.

The next challenge is to examine the mechanism of electron transfer, Yang adds. 'The excited electrons in these dyes are supposed to be injected into the semiconductor through the acceptor moiety rather than the lateral anchoring group. More experimental studies of the behaviour of these dyes on the surface and the electron injection pathways need to be conducted,' he says.

Edward Morgan

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