Demonstration of a Gel-Polymer Electrolyte-Based Electrochromic Device Outperforming Its Solution-Type Counterpart in All Merits: Architectural Benefits of CeO₂ Quantum Dot and Nanorods

For years, solution-type electrochromic devices (ECDs) have intrigued researchers’ interest and eventually rendered themselves into commercialization. Regrettably, challenges such as electrolyte leakage, high flammability, and complicated edge-encapsulation processes limit their practical utilization, hence necessitating an efficient alternate. In this quest, although the concept of solid/gel-polymer electrolyte (SPE/GPE)-based ECDs settled some issues of solution-type ECDs, an array of problems like high operating voltage, sluggish response time, and poor cycling stability have paralyzed their commercial applicability. Herein, we demonstrate a choreographed-CeO2-nanofiller-doped GPE-based ECD outperforming its solution-type counterpart in all merits. The filler-incorporated polymer electrolyte assembly was meticulously weaved through the electrospinning method, and the resultant host was employed for immobilizing electrochromic viologen species. The filler engineering benefits conceived through the tuned shape of CeO2 nanorod and quantum dots, along with the excellent redox shuttling effect of Ce3+/Ce4+, synchronously yielded an outstanding class of GPE, which upon utilization in ECDs delivered impressive electrochromic properties. A combination of features possessed by a particular device (QD-NR/PVDF-HFP/IL/BzV-Fc ECD) such as exceptionally low driving voltage (0.9 V), high transmittance change (ΔT, ∼69%), fast response time (∼1.8 s), high coloration efficiency (∼339 cm2/C), and remarkable cycling stability (∼90% ΔT-retention after 25,000 cycles) showcased a striking potential in the yet-to-realize market of GPE-based ECDs. This study unveils the untapped potential of choreographed nanofillers that can promisingly drive GPE-based ECDs to the doorstep of commercialization

Demonstration of a Gel-Polymer Electrolyte-Based Electrochromic Device Outperforming Its Solution-Type Counterpart in All Merits: Architectural Benefits of CeO₂ Quantum Dot and Nanorods

For years, solution-type electrochromic devices (ECDs) have intrigued researchers’ interest and eventually rendered themselves into commercialization. Regrettably, challenges such as electrolyte leakage, high flammability, and complicated edge-encapsulation processes limit their practical utilization, hence necessitating an efficient alternate. In this quest, although the concept of solid/gel-polymer electrolyte (SPE/GPE)-based ECDs settled some issues of solution-type ECDs, an array of problems like high operating voltage, sluggish response time, and poor cycling stability have paralyzed their commercial applicability. Herein, we demonstrate a choreographed-CeO2-nanofiller-doped GPE-based ECD outperforming its solution-type counterpart in all merits. The filler-incorporated polymer electrolyte assembly was meticulously weaved through the electrospinning method, and the resultant host was employed for immobilizing electrochromic viologen species. The filler engineering benefits conceived through the tuned shape of CeO2 nanorod and quantum dots, along with the excellent redox shuttling effect of Ce3+/Ce4+, synchronously yielded an outstanding class of GPE, which upon utilization in ECDs delivered impressive electrochromic properties. A combination of features possessed by a particular device (QD-NR/PVDF-HFP/IL/BzV-Fc ECD) such as exceptionally low driving voltage (0.9 V), high transmittance change (ΔT, ∼69%), fast response time (∼1.8 s), high coloration efficiency (∼339 cm2/C), and remarkable cycling stability (∼90% ΔT-retention after 25,000 cycles) showcased a striking potential in the yet-to-realize market of GPE-based ECDs. This study unveils the untapped potential of choreographed nanofillers that can promisingly drive GPE-based ECDs to the doorstep of commercialization

Synthesis of Redox Polymer Nanobeads and Nanocomposites for Glucose Biosensors

Redox polymer nanobeads of branched polyethylenimine binding with ferrocene (BPEI-Fc) were synthesized using a simple chemical process. The functionality and morphology of the redox polymer nanobeads were investigated by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). This hydrophilic redox nanomaterial could be mixed with glucose oxidase (GOx) for drop-coating on a screen-printed carbon electrode (SPCE) for glucose sensing application. Electrochemical properties of the BPEI-Fc/GOx/SPCE prepared under different conditions were studied by cyclic voltammetry (CV). On the basis of these CV results, the synthetic condition of the BPEI-Fc/GOx/SPCE could be optimized. By incorporating conductive poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS), the performance of a redox polymer nanobead–based enzyme electrode could be further improved. The influence of PEDOT:PSS on the nanocomposite enzyme electrode was discussed from the aspects of the apparent electron diffusion coefficient (<i>D</i>_app) and the charge transfer resistance (<i>R</i>_ct). The glucose-sensing sensitivity of the BPEI-Fc/PEDOT:PSS/GOx/SPCE is calculated to be 66 μA mM^–1 cm^–2, which is 2.5 times higher than that without PEDOT:PSS. The apparent Michaelis constant (<i>K</i>_M^app) of the BPEI-Fc/PEDOT:PSS/GOx/SPCE estimated by the Lineweaver–Burk plot is 2.4 mM, which is much lower than that of BPEI-Fc/GOx/SPCE (11.2 mM). This implies that the BPEI-Fc/PEDOT:PSS/GOx/SPCE can catalytically oxidize glucose in a more efficient way. The interference test was carried out by injection of glucose and three common interferences: ascorbic acid (AA), dopamine (DA), and uric acid (UA) at physiological levels. The interferences of DA (4.2%) and AA (7.8%) are acceptable and the current response to UA (1.6%) is negligible, compared to the current response to glucose

Earth Abundant Silicon Composites as the Electrocatalytic Counter Electrodes for Dye-Sensitized Solar Cells

Earth abundant silicon compounds, including Si₃N₄, SiO₂, SiS₂, and SiSe₂, were introduced as the electrocatalytic materials for the counter electrodes (CE) in dye-sensitized solar cells (DSSCs). Among these silicon-based materials, Si₃N₄, SiS₂, and SiSe₂ were applied in DSSCs for the first time. In the presence of a conducting binder, poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS), various silicon-based composites (Si₃N₄/PEDOT:PSS, SiO₂/PEDOT:PSS, SiS₂/PEDOT:PSS, and SiSe₂/PEDOT:PSS) were successfully coated on the ITO substrates via a simple drop-coating process. In a composite film, silicon-based nanoparticles provided attractive electrocatalytic ability and plenty of electrocatalytic active sites for the triiodine ion (I₃^–) reduction. PEDOT:PSS not only acted as a good conducting binder for silicon-based nanoparticles, but also provided a continuous polymer matrix to increase the electron transfer pathways. By adjusting the weight percent (1–5 wt %) of the silicon-based nanoparticles (Si₃N₄, SiO₂, SiS₂, and SiSe₂) with respect to the weight of PEDOT:PSS, the composite films containing 5 wt % Si₃N₄ (denoted as Si₃N₄-5) and 5 wt % SiSe₂ (denoted as SiSe₂-5) both reached excellent electrocatalytic abilities and rendered the good cell efficiencies (η) of 8.2% to their DSSCs. It can be said that both Si₃N₄-5 and SiSe₂-5 are promising electrocatalytic materials to replace the rare and expensive Pt (η = 8.5%)

Organic Dyes Containing Fluorene Decorated with Imidazole Units for Dye-Sensitized Solar Cells

New organic dyes containing fluorene functionalized with two imidazole chromophores as donors and cyanoacrylic acid acceptors have been synthesized and successfully demonstrated as sensitizers in nanocrystalline TiO₂-based dye-sensitized solar cells (DSSCs). The monoimidazole analogues were also synthesized for comparison. The Sommelet reaction of bromomethylated 2-bromo-9,9-diethyl-9<i>H</i>-fluorene produced the key precursor 7-bromo-9,9-diethyl-9<i>H</i>-fluorene-2,4-dicarbaldehyde required for the preparation of imidazole-functionalized fluorenes. Since the dyes possess weak donor segment, the electron-richness of the conjugation pathway dictated the optical, electrochemical, and photovoltaic properties of the dyes. The dyes served as sensitizers in DSSC and exhibited moderate efficiency up to 3.44%. The additional imidazole present on the fluorene has been found to retard the electron recombination due to the bulkier hydrophobic environment and led to high open-circuit voltage in the devices

Organic Dyes Containing Carbazole as Donor and π‑Linker: Optical, Electrochemical, and Photovoltaic Properties

A series of new metal free organic dyes containing carbazole as donor and π-linker have been synthesized and characterized as effective sensitizers for dye sensitized solar cells (DSSCs). The carbazole functionalized at C-2 and C-7 served as electron-rich bridge. The donor property of the carbazole is substantially enhanced on introduction of <i>tert</i>-butyl groups at C-3 and C-6 positions and the oxidation propensity of the dyes increased on insertion of thiophene unit in the conjugation pathway. These structural modifications fine-tuned the optical and electrochemical properties of the dyes. Additionally, the presence of <i>tert</i>-butyl groups on the carbazole nucleus minimized the intermolecular interactions which benefited the performance of DSSCs. The dyes served as efficient sensitizers in DSSCs owing to their promising optical and electrochemical properties. The efficiency of DSSCs utilizing these dyes as sensitizers ranged from 4.22 to 6.04%. The <i>tert</i>-butyl groups were found to suppress the recombination of injected electrons which contributed to the increment in the photocurrent generation (<i>J</i>_SC) and open circuit voltage (<i>V</i>_OC). A dye with carbazole donor functionalized with <i>tert</i>-butyl groups and the conjugation bridge composed of 2,7-disubstituted carbazole and thiophene fragments exhibited higher <i>V</i>_OC value. However, the best device efficiency was observed for a dye with unsubstituted carbazole donor and the π-linker featuring carbazole and bithiophene units due to the high photocurrent generation arising from the facile injection of photogenerated electrons into the conduction band of titanium dioxide (TiO₂) facilitated by the low-lying LUMO

Fluorene-Based Sensitizers with a Phenothiazine Donor: Effect of Mode of Donor Tethering on the Performance of Dye-Sensitized Solar Cells

Two types of fluorene-based organic dyes featuring T-shape/rod-shape molecular configuration with phenothiazine donor and cyanoacrylic acid acceptor have been synthesized and characterized as sensitizers for dye-sensitized solar cells. Phenothiazine is functionalized at either nitrogen (N10) or carbon (C3) to obtain T-shape and rod-like organic dyes, respectively. The effect of structural alternation on the optical, electrochemical, and the photovoltaic properties is investigated. The crystal structure determination of the dye containing phenyl linker revealed cofacial slip-stack columnar packing of the molecules. The trends in the optical properties of the dyes are interpreted using time-dependent density functional theory (TDDFT) computations. The rod-shaped dyes exhibited longer wavelength absorption and low oxidation potentials when compared to the corresponding T-shaped dyes attributable to the favorable electronic overlap between the phenothiazine unit and the rest of the molecule in the former dyes. However, the T-shaped dyes showed better photovoltaic properties due to the lowest unoccupied molecular orbital (LUMO) energy level favorable for electron injection into the conduction band of TiO₂ and appropriate orientation of the phenothiazine unit rendering effective surface blocking to suppress the recombination of electrons between the electrolyte I₃^– and TiO₂. The electrochemical impedance spectroscopy investigations provide further support for the variations in the electron injection and transfer kinetics due to the structural modifications

Fluorene-Based Sensitizers with a Phenothiazine Donor: Effect of Mode of Donor Tethering on the Performance of Dye-Sensitized Solar Cells

Two types of fluorene-based organic dyes featuring T-shape/rod-shape molecular configuration with phenothiazine donor and cyanoacrylic acid acceptor have been synthesized and characterized as sensitizers for dye-sensitized solar cells. Phenothiazine is functionalized at either nitrogen (N10) or carbon (C3) to obtain T-shape and rod-like organic dyes, respectively. The effect of structural alternation on the optical, electrochemical, and the photovoltaic properties is investigated. The crystal structure determination of the dye containing phenyl linker revealed cofacial slip-stack columnar packing of the molecules. The trends in the optical properties of the dyes are interpreted using time-dependent density functional theory (TDDFT) computations. The rod-shaped dyes exhibited longer wavelength absorption and low oxidation potentials when compared to the corresponding T-shaped dyes attributable to the favorable electronic overlap between the phenothiazine unit and the rest of the molecule in the former dyes. However, the T-shaped dyes showed better photovoltaic properties due to the lowest unoccupied molecular orbital (LUMO) energy level favorable for electron injection into the conduction band of TiO₂ and appropriate orientation of the phenothiazine unit rendering effective surface blocking to suppress the recombination of electrons between the electrolyte I₃^– and TiO₂. The electrochemical impedance spectroscopy investigations provide further support for the variations in the electron injection and transfer kinetics due to the structural modifications

Benzimidazole-Branched Isomeric Dyes: Effect of Molecular Constitution on Photophysical, Electrochemical, and Photovoltaic Properties

Three benzimidazole-based isomeric organic dyes possessing two triphenylamine donors and a cyanoacrylic acid acceptor are prepared by stoichiometrically controlled Stille or Suzuki–Miyaura coupling reaction which predominantly occurs on the <i>N</i>-butyl side of benzimidazole due to electronic preferences. Combined with the steric effect of the <i>N</i>-butyl substituent, placement of the acceptor segment at various nuclear positions of benzimidazole such as C2, C4, and C7 led to remarkable variations in intramolecular charge transfer absorption, electron injection efficiency, and charge recombination kinetics. The substitution of acceptor on the C4 led to red-shifted absorption, while that on C7 retarded the charge transfer due to twisting in the structure caused by the butyl group. Because of the cross-conjugation nature and poor electronic interaction between the donor and acceptor, the dye containing triphenylamine units on C4 and C7 and the acceptor unit on C2 showed the low oxidation potential. Thus, this dye possesses favorable HOMO and LUMO energy levels to render efficient sensitizing action in solar cells. Consequently, it results in high power conversion efficiency (5.01%) in the series with high photocurrent density and open circuit voltage. The high photocurrent generation by this dye is reasoned to it exceptional charge collection efficiency as determined from the electron impedance spectroscopy

Tunable Electrofluorochromic Device from Electrochemically Controlled Complementary Fluorescent Conjugated Polymer Films

The fluorescent behavior of the electrofluorochromic devices (Type I) of greenish-yellow emitting <b>P1</b> and blue emitting <b>P2</b> can be reversibly switched between the nonfluorescent (oxidized) state and the fluorescent (neutral) state with a superb on/off ratio of 23.8 and 21.9, respectively. Moreover, a tunable electrofluorochromic device (Type II) based on two <b>P1</b> and <b>P2</b> polymeric layers that are coated individually on two independent ITO electrodes shows switchable blue-white-(greenish-yellow) multifluorescence states