Manuel Pietsch1 2 Johannes Zimmermann1 2 Tobias Rödlmeier1 2 Stefan Schlisske1 2 Carlos Romero-Nieto3 Gerardo Hernandez-Sosa1 2

1, LTI, Karlsruher Institute of Technology, Karlsruhe, , Germany
2, KIT, InnovationLab GmbH, Heidelberg, , Germany
3, OCI, Ruprecht-Karls-University Heidelberg, Heidelberg, , Germany

Electrofluorochromic devices (EFCD) receive increasing attention in investigation in the past years, because they offer the possibilities for dual-mode display devices, which combine the advantages of reflective and emissive displays. Besides that, the low power consumption, the low voltage requirement and simple device architecture (i.e. electrochemical cell) provide the opportunity for low-cost display devices. To provide a cost-effective method with the freedom of design necessary for smart windows and display applications, inkjet printing can be used as a suitable method with high throughput, low material waste and upscaling capabilities to industrial fabrication.
Here, we report the synchronous electrochromic and electrofluorochromic switching of polyindenofluorene-8-tryarylamine (PIF8-TAA). The investigated devices consisted of a layer of PIF8-TAA and a polymer electrolyte gel (PEG), using poly(methyl methacrylate) (PMMA), tetrabutylammonium hexafluorophosphate (TBAPF6) and propylene carbonate (PC), sandwiched between two indium tin oxide (ITO) electrodes. In its neutral state the polymer is transparent in the visible range and changes its color to deep red upon oxidation. Simultaneously, the blue colored fluorescence intensity is quenched. Besides its high stability in ambient conditions, the devices showed switching times of <2s, a coloration efficiency of 542±10cm2/C at 395nm, a fluorescence contrast ratio of 4,1±0,3 and an electrochromic contrast of 50±4% in the visible spectrum. These figures of merit ranking in the upper range of literature values make it a promising material for dual-mode display applications. Furthermore, by changing the working electrode to inkjet printed poly(3,4-ethylenedioxythiophene) (PEDOT) we demonstrate the fabrication of an electrofluorochromic device with independently addressable pixels to demonstrate the functionality of inkjet printed, structured EFCDs. Thus demonstrating the potential of these devices in display and smart window applications.