5 research outputs found
Electrochromic organic and polymeric materials for display applications
An electrochromic material is one where a reversible color change takes place upon
reduction (gain of electrons) or oxidation (loss of electrons), on passage of electrical current
after the application of an appropriate electrode potential. In this review the general field of
electrochromism is introduced, with coverage of the types, applications, and chemical classes
of electrochromic materials and the experimental methods that are used in their study. The
main classes of electrochromic organic and polymeric materials are then surveyed, with
descriptions of representative examples based on transition metal coordination complexes,
viologen systems, and conducting polymers. Examples of the application of such organic and
polymeric electrochromic materials in electrochromic displays are given
Optimization of PEDOT Films in Ionic Liquid Supercapacitors: Demonstration As a Power Source for Polymer Electrochromic Devices
We
report on the optimization of the capacitive behavior of polyÂ(3,4-ethylenedioxythiophene)
(PEDOT) films as polymeric electrodes in flexible, Type I electrochemical
supercapacitors (ESCs) utilizing ionic liquid (IL) and organic gel
electrolytes. The device performance was assessed based on figures
of merit that are critical to evaluating the practical utility of
electroactive polymer ESCs. PEDOT/IL devices were found to be highly
stable over hundreds of thousands of cycles and could be reversibly
charged/discharged at scan rates between 500 mV/s and 2 V/s depending
on the polymer loading. Furthermore, these devices exhibit leakage
currents and self-discharge rates that are comparable to state of
the art electrochemical double-layer ESCs. Using an IL as device electrolyte
allowed an extension of the voltage window of Type I ESCs by 60%,
resulting in a 2.5-fold increase in the energy density obtained. The
efficacies of tjese PEDOT ESCs were assessed by using them as a power
source for a high-contrast and fast-switching electrochromic device,
demonstrating their applicability in small organic electronic-based
devices
An Electrochromic Painter’s Palette: Color Mixing via Solution Co-Processing
Electrochromic polymers (ECPs) have
been shown to be synthetically
tunable, producing a full palette of vibrantly colored to highly transmissive
polymers. The development of these colored-to-transmissive ECPs employed
synthetic design strategies for broad color targeting; however, due
to the subtleties of color perception and the intricacies of polymer
structure and color relationships, fine color control is difficult.
In contrast, color mixing is a well-established practice in the printing
industry. We have identified three colored-to-transmissive switching
electrochromic polymers, referred to as ECP-Cyan (ECP-C), ECP-Magenta
(ECP-M), and ECP-Yellow (ECP-Y), which, via the co-processing of multicomponent
ECP mixtures, follow the CMY color mixing model. The presented work
qualitatively assesses the thin film characteristics of solution co-processed
ECP mixtures. To quantitatively determine the predictability of the
color properties of ECP mixtures, we estimated mass extinction coefficients
(ε<sub>mass</sub>) from solution spectra of the CMY ECPs and
compared the estimated and experimentally observed color values of
blends via a calculated color difference (Δ<i>E</i><sub>ab</sub>). The values of Δ<i>E</i><sub>ab</sub> range from 8 to 26 across all mixture compositions, with an average
value of 15, representing a reasonable degree of agreement between
predicted and observed color values. We demonstrate here the ability
to co-process ECP mixtures into vibrantly colored, visually continuous
films and the ability to estimate the color properties produced in
these mixed ECP films
Follow the Yellow Brick Road: Structural Optimization of Vibrant Yellow-to-Transmissive Electrochromic Conjugated Polymers
A series of conjugated polymers were
designed and synthesized to
extract structure–property relationships with the goal of yielding
yellow-to-transmissive switching electrochromes. The polymers are
based on repeat units of propylenedioxythiophene (ProDOT) in alternation
with a variety of arylenes including 1,4-phenylene (ProDOT-Ph), 2,7-fluorene
(ProDOT-Fl), 2,7-carbazole (ProDOT-Cbz), 2,5-dimethoxy-1,4-phenylene
(ProDOT-PhÂ(MeO)<sub>2</sub>), and 2,7-pyrene (ProDOT-Py). Additionally,
a random copolymer containing ProDOT and two different arylene units
was produced: ProDOT-phenylene-ProDOT-dimethoxyphenylene (R-ProDOT-Ph/PhÂ(MeO)<sub>2</sub>) and two polymers with a ProDOT dimer in alternation with
pyrene and phenylene composed ProDOT<sub>2</sub>-pyrene (ProDOT<sub>2</sub>-Py) and ProDOT<sub>2</sub>-phenylene (ProDOT<sub>2</sub>-Ph),
respectively. The polymers were synthesized using Suzuki polycondensation.
Examinations of the optoelectronic properties via UV–vis–NIR
spectroscopy, differential pulse voltammetry, and spectroelectrochemistry
show that varying the electron richness of the polymer by utilizing
more electron rich arylenes, dimers of ProDOT, or less electron rich
arylenes, the oxidation potential could be decreased or increased,
respectively, ranging from 270 to 650 mV. Through subtle C–H <i>ortho</i> interactions from the arylene unit, yellow neutral
state colors were maintained with transmissive or near-transmissive
oxidized states. Colorimetry utilizing <i>L</i>*<i>a</i>*<i>b</i>*, where <i>a</i>*<i>b</i>* values correlate to the chroma or saturation of a color
(note: −<i>a</i>* and +<i>a</i>* correspond
to green and red and −<i>b</i>* and +<i>b</i>* correspond to blue and yellow, respectively) and <i>L</i>* represents the lightness, was used to show the maintenance of yellow
colors in the neutral states. Herein, the yellow polymers had <i>L</i>* values above 84.0, <i>a</i>* values ranging
from −11.6 to 24.8, and <i>b</i>* values greater
than 47.6. In the oxidized states, the most transmissive forms had <i>L</i>* values above 70.0, <i>a</i>* values ranging
from −2.1 to 2.0, and <i>b</i>* values ranging from
−6.8 to −0.1. These structure–property relationships
grant access to conjugated polymers with high energy absorbance in
the visible, while allowing variability in redox potentials, providing
a deeper understanding in yielding yellow-to-transmissive electrochromic
polymers
Poly[Bis-EDOT-Isoindigo]: An Electroactive Polymer Applied to Electrochemical Supercapacitors
PolyÂ[6,6′-bisÂ(ethylene-3,4-dioxythien-2-yl)]-<i>N</i>,<i>N</i>′-dialkylisoindigo (PBEDOT-iI)
was synthesized
and incorporated as an electroactive material into electrochemical
supercapacitors (ESCs) in type I and type III configurations. In type
I ESCs, PBEDOT-iI provides a specific power of ∼360 W/kg and
specific energy of ∼0.5 Wh/kg, while retaining about 80% of
its electroactivity over 10 000 cycles. In addition, we report
on the use of PBEDOT-iI in type III supercapacitors where operating
voltages as high as 2.5 V were achieved with specific energies of
ca. 15 Wh/kg, albeit with limited stability