Issue 41, 2021

Critical role of H-aggregation for high-efficiency photoinduced charge generation in pristine pentamethine cyanine salts

Abstract

The mechanism of photoinduced symmetry-breaking charge separation in solid cyanine salts at the base of organic photovoltaic and optoelectronic devices is still debated. Here, we employ femtosecond transient absorption spectroscopy (TAS) to monitor the charge transfer processes occurring in thin films of pristine pentamethine cyanine (Cy5). Oxidized dye species are observed in Cy5-hexafluorophosphate salts upon photoexcitation, resulting from electron transfer from monomer excited states to H-aggregates. The charge separation proceeds with a quantum yield of 86%, providing the first direct proof of high efficiency intrinsic charge generation in organic salt semiconductors. The impact of the size of weakly coordinating anions on charge separation and transport is studied using TAS alongside electroabsorption spectroscopy and time-of-flight techniques. The degree of H-aggregation decreases with increasing anion size, resulting in reduced charge transfer. However, there is little change in carrier mobility, as despite the interchromophore distance increasing, the decrease in energetic disorder helps to alleviate the trapping of charges by H-aggregates.

Graphical abstract: Critical role of H-aggregation for high-efficiency photoinduced charge generation in pristine pentamethine cyanine salts

Supplementary files

Article information

Article type
Paper
Submitted
16 Jul 2021
Accepted
08 Oct 2021
First published
08 Oct 2021
This article is Open Access
Creative Commons BY-NC license

Phys. Chem. Chem. Phys., 2021,23, 23886-23895

Critical role of H-aggregation for high-efficiency photoinduced charge generation in pristine pentamethine cyanine salts

G. C. Fish, J. M. Moreno-Naranjo, A. Billion, D. Kratzert, E. Hack, I. Krossing, F. Nüesch and Jacques-E. Moser, Phys. Chem. Chem. Phys., 2021, 23, 23886 DOI: 10.1039/D1CP03251H

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