27.04.2018 Organic salt semiconductors with surprising optical and electronic properties

Prof. Dr. Frank A. Nüesch, Abteilungsleiter, Abteilung Funktionspolymere, EMPA Materials Science & Technology, Dübendorf, Switzerland

Date: Friday, 04.05.2018, 10:15 h
Location: Department of Physics, Renthof 6, seminar room 00014

Abstract

Cyanines represent a class of charged chromophores with an odd number of π-conjugated carbons. Today they are most widely employed as bio labels for fluorescent imaging. Originally cyanine dyes were developed as sensitizers for the photographic technology, but only very few research groups have assessed this class of materials as organic semiconductors.

These dyes however provide unique spectral features. For example, the strong near infrared absorption can be exploited in transparent devices¹, for example as NIR sensitive photodetectors², light-emitting electrochemical cells³ or in up-conversion devices. An interesting peculiarity that arises in the solid state is linked to the cationic nature of the chromophore. As we have shown for certain pentamethine cyanine dyes⁴, charges can be generated and extracted in pristine cyanine films with high quantum yield owing to the very slow carrier recombination rate which we attribute to a charge screening effect. This particular charge generation mechanism obviates the need of a heterogeneous donor-acceptor interface, which in general is mandatory for efficient cyanine based solar cells⁵.

¹ A. Véron et al., Org. Lett., 2014, 16 (4), 1044
² H. Zhang et al., Sci. Rep. 2015, 5, 9439
³ S. Jenatsch et al., ACS Appl. Mater. Interfaces, 2016, 8 (10), 6554
⁴ L. Wang et al., Adv. Funct. Mater., 2018, 1705724
⁵ Andrius Devizis et al., J. Am. Chem. Soc., 2015, 137, 8192

Empa, Swiss Federal Institute for Materials Science and Technology, Laboratory for Functional Polymers, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
and
Institut des Matériaux, Ecole Polytechnique Fédérale de Lausanne, EPFL, Station 12, CH-1015 Lausanne, Switzerland