POLYMERIC CYANINE DYES - NOVEL NIR ABSORBERS
Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Functional Polymers, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
Due to recent developments in the field of organic photovoltaic and organic light-emitting devices there has been a renewed great interest in the area of tailor-made “functionalized” organic dyes. Particular attention is given to materials with high absorption coefficients, advantageous exciton diffusion coefficient as well as high charge carrier mobility. In order to bring the efficiency of organic solar cells to a technologically acceptable level it is desirable not only to improve charge separation and transportation, but also to develop materials that absorb in the near infrared (NIR) spectral domain, accounting for more than one third of the total photon flux coming from the sun.
In this context polymeric cyanine dyes were identified as promising candidates. We developed various polymeric cyanine dyes (1, 2) using different synthetic routes. Polymers with a moderate molecular weight (10- 20 kg/mol) and narrow distribution were synthesized showing an absorption maximum in the range of 700 to 1000 nm. The lowest electronic band gap for the heptamethine dye was determined at 0.88 eV. All polymers are thermally stable up to high temperatures (307 °C for 1 and 275 °C for 2) and soluble in DMSO and 2,2,2-trifluoroethanol.
The present work focuses on synthesis and analytic characterization of the polymeric cyanine dyes. First applications are also discussed.