Photostability of Ambient-Processed, Conjugated Polymer Electrochromic Devices Encapsulated by Bioderived Barrier Films

Abstract

Polymer-based electrochromic devices (ECDs) are a promising technology for enabling low-voltage, disposable displays, yet are currently limited by photo-oxidative bleaching of the active materials. Here, renewable barrier films composed of cellulose and chitin are presented as an alternative to poly­(ethylene terephthalate) (PET) for encapsulating ECDs. To assess barrier film effectiveness, lateral ECDs composed of poly­(3,4-propylenedioxythiophene-(CH2OEtHx)2) (P­(ProDOT)) active layers were constructed and encapsulated with a multilayer barrier consisting of chitin nanofibers and cellulose nanocrystals spray cast onto a cellulose acetate substrate (oxygen transmission rate (OTR) = 29 cm3 m–2 day–1), a commercially available PET film (OTR = 8.5 cm3 m–2 day–1), and a high-performance PET-Al2O3 multilayer barrier film (OTR < 1 cm3 m–2 day–1). The photodegradation of the P­(ProDOT) active layer was determined by measuring the evolution of the colorimetric contrast (ΔE*) and switching speeds as a function of light exposure (100 mW cm–2, AM 1.5 G light). Photodegradation was found to proceed at a similar rate for all encapsulated devices (roughly 10 times more slowly than unencapsulated devices), highlighting the opportunity for replacing petroleum packaging with bioderived barrier films. Analysis of the switching kinetics, the shifts in optical absorbance, and evidence of chemical degradation indicate that both photochemical breakdown of the electrolyte and cross-linking of the P­(ProDOT) active material are key drivers for loss of device performance when oxygen flux to the active material is limited. Pathways toward better understanding photodegradation are then proposed with sustainability in mind for future ECD design.

Aqueous-Based Recycling of Cellulose Nanocrystal/Chitin Nanowhisker Barrier Coatings

“…Though recycling resulted in a slight increase in the haze, these coated films had low haze (<10%) in the range of 400–700 nm, except PET-rChNW2-rCNC2 (36.4%). Generally, the high transmittance and low haze of the coated films also make them potential substitutes for applications other than food packaging, such as electrochromic device packaging …”

“…Generally, the high transmittance and low haze of the coated films also make them potential substitutes for applications other than food packaging, such as electrochromic device packaging. 53 Admittedly, numerous challenges need to be overcome to use PET-ChNW-CNC in practice. For instance, handling a waste stream usually involves a prewashing step to remove package contents, i.e., food waste, using water or an alkaline solution.…”

Optimization of spray-coated nanochitin/nanocellulose films as renewable oxygen barrier layers via thermal treatment

“…The high transmittance and low haze of our bilayer films support their use in potential applications such as electronic device packaging as well as food packaging. 52…”

Degradation Pathways of Conjugated Radical Cations

“…Despite many unique features of organic materials, significant concerns regarding stability and durability continue to cast doubt on the practical applicability of organic electronic devices . Studies on organic photovoltaic devices, light-emitting diodes, and electrochromic devices have illustrated the deterioration of active materials, as well as other underlying charge-transfer layers and conductors during device operation, exacerbated by the presence of ambient oxygen, moisture, exposure to sunlight and heat. − Mechanical , and electrochemical degradation , of redox-active molecules and electrolytes can further complicate the degradation process. Impact of the intrinsic reactivity of π-conjugated molecules on the overall device degradation is difficult to establish due to the interplay of different factors involving multiple device components.…”