Motivation and Aim of the Dissertation

Motivation

Electrochromism is defined as a phenomenon in which a color of material can be changed upon voltage application, leading to distinct colored states at different redox states. In an in-creasingly connected world full of smart objects and devices, electrochromic materials-based systems have the potential to become the most practical and widely deployable human inter-faces for ambient intelligence. By bringing graphics and surinter-faces to life on consumer products and throughout our everyday living environments, electrochromic materials printed, coated as thin-films and further processed into end-products, create immensely diverse opportunities for the creative industries and the design and manufacture of new added-value applications for electrochromic materials.

Recently, electrochromic devices (ECDs) have been exploited for their use in smart con-sumer items or environmental areas including labels, lifestyle, wearables, security and design, displaying valuable information for users.^1–9 As an example, Ynvisible^® company has been de-veloping within the market of smart labels for packaging, safety tags, health monitorization, embedding ECDs on everyday products promoting an ubiquitous presence of these displays as non-intrusive forms of communication, using electrochromism as a technology.⁹ Such dis-plays present advantages like their flexibility, low power consumption and a vast number of possible solutions for an intelligent environment.

In the last years, polythiophene-based materials have been highly studied and devel-oped for electrochromic applications due to their remarkable electrochromic properties in terms of the color palette, color contrast and simple processability. In particular, Reynolds’s group has offered a large contribution in the past years, exploring a large range of chemical structures and electrochromic properties of polythiophene materials.^10–14 Yet, their implemen-tation at an industrial scale, except for the well-known poly(3,4-ethylenedioxythiophene) (PE-DOT), is still hampered by stability issues. Indeed, during my almost 3 years’ experience work-ing in Ynvisible^® as an early-stage researcher, developing and producing electrochromic mate-rials and devices, I was directly in contact with the limitations of polythiophenes that despite the vast color palette, still do not present viable long-term processability and stability to be used in ECDs for practical applications. Similarly, to other type of semiconducting problems, polythiophene materials lack on solubility except for toxic organic solvents such as chloroform or toluene, resulting in simple, but limited processability. Additionally, polythiophene mate-rials present low electrical conductivity, poor chemical stability and cycling stability that limit their use in electrochromic devices for a higher number of applications.¹⁵ The limited use, processability and stability of polythiophene materials for solid-state ECDs, increases the mo-tivation on developing solutions to take advantage of the remarkable properties of these ma-terials such as their opto-electronic properties and vast color pallet for electrochromic applica-tions. Additionally, one of the key components of electrochromic devices is the conductive layer that, in the majority of the displays, is constituted by indium-tin-oxide (ITO) coatings.

Due to the global raw materials consumption issues, indium low availability and high produc-tion cost of materials like ITO, the necessity of a green and viable soluproduc-tion for transparent and conductive electrodes also emerges.

Aim

The aim of this work is to develop new nanostructured polythiophene-based electrochromic materials and assemble solid-state ECDs towards an enhancement of the current state-of-the-art on electrochromism. The work here produced and presented is focused on the production of nanostructured polythiophene materials through the design, synthesis, and characterization of new electrochromic polymers as well as their nanostructuration using two different strate-gies.

Firstly, via a direct nanostructuration of a well-known polythiophene like poly(3-hexyxlthiophene-2,5-diyl) (P3HT) through the formation of water-dispersible nanoparticles

using the nanoprecipitation method. The nanostructuration of polythiophene materials is fur-ther studied on a new class of polymers designed and synthesized, focused on the yellow col-oration. Secondly, through the formation of hybrid nanostructured thin film composites using nanotemplates such as carbon nanotubes (CNTs) or copper nanowires (CuNWs).

Despite the unquestionable advantages that polythiophene-based materials can offer such as their low bandgap (which generates intrinsic semiconductive characteristics), easily tunable opto-electronic properties through simple synthetic procedures, increased color pallet for electrochromic applications and simple processability; the solid-state morphology of these materials in electrochromic displays, their limited processability and their poor chemical sta-bility tightens their use in electrochromic applications through solid-state ECDs.

Furthermore, the purpose of this work aspires to an improvement of polythiophene-based materials through an optimization and comprehensive study on the impact of:

- The overall performance of solid-state electrochromic devices using polythiophene nanoparticles (switching time, color contrast, durability) while using processable water-based solutions;

- The design and synthesis of a new class of compounds targeting yellow colored polythiophenes with low redox potential;

- The use of organic-inorganic hybrid materials as thin films to enhance electro-chromic performances and;

- The use of new alternatives to ITO as transparent and conductive electrodes for electrochromic applications.

Each point addressed above will be important to reach the goal by optimization of the design and synthesis, as well as the employment of each new developed system on solid-state electrochromic devices, to achieve enhanced electrochromic performances which represent a real improvement on the current state-of-the-art on electrochromic applications.

Framework

The work presented in this thesis was developed during the period where two European jects were running, simultaneously. The collaborations coming from those two European pro-jects allowed the author to establish several connections and create a framework that offered a crucial contribution to the work. At the same time, the continuous collaboration between the CHARM (Cultural Heritage and Responsive Materials) group at NOVA School of Science and Technology¹⁶ and Ynvisible^{® 17} was present throughout the time of this dissertation by kindly

providing materials, feedback, and know-how on the assembly of solid-state electrochromic devices.

The synthesis and formation of water-dispersible nanoparticles is investigated, through a collaboration between the CHARM group and Mediteknology^® located at the CNR-ISOF in Bologna,¹⁸ Italy, on the scope of an EU H2020-MSCA-RISE 2020 project with reference 734834 – INFUSION.¹⁹ Mediteknology^® possesses a vast know-how on the synthesis, character-ization of polythiophene-based materials and their nanostructuration in water-dispersible na-noparticles for different applications.²⁰

The development of hybrid nanostructured thin film composites using nanotemplates is disclosed through a collaboration with the Bonifazi Group in the University of Vienna,²¹ Aus-tria led by professor Davide Bonifazi and the Nanochemistry Laboratory in the University of Strasbourg,²² France, led by Professor Paolo Samori on the scope of an EU H2020 programme reference nº760973 – DECOCHROM.²³ With the expertise of Bonifazi Group on the use of car-bon-based materials and the knowledge of the Nanochemistry Laboratory on multicomponent nanostructures and networks for optoelectronic applications; the design and development of a system capable of enhancing the electrochromic properties of polythiophene materials in solid-state devices and the development of a viable alternative for indium-tin-oxide (ITO) as transparent and conductive layer for ECDs are investigated.