A dual-mode electrochromic and thermochromic smart window utilizing a polyzwitterionic hydrogel.

Abstract In order to address the key bottlenecks in Prussian blue (PB)-based electrochromic devices-including low crystallinity, sluggish ion diffusion kinetics, and weak interfacial bonding. This study proposes a multidimensional synergistic modification strategy using 2D MXene. Through a combination of molecular structural and electrochemical testing, the study systematically elucidates the modification mechanism of MXene and its performance optimization effects. The results of the study indicate that MXene enhances PB performance through the synergistic effects of interfacial bonding, structural support, and electronic regulation. The results of this study demonstrate that the formation of Fe-O-Ti coordination bonds and the establishment of physical anchoring enhance the adhesion strength between PB films and substrates by approximately 5.4 times. MXene has been demonstrated to promote PB crystallization as a heterogeneous nucleation site. The hybridization of Ti 3d and PB orbitals results in a reduction of the bandgap from 2.18 eV to 1.92 eV, thereby increasing the carrier density by a factor of 4.03. PB-M demonstrates a diffusion coefficient that is 5.1 times greater than that of pure PB, accompanied by markedly diminished charge transfer resistance and diffusion resistance in comparison to pure PB films. Meanwhile, the flexible network formed by MXene buffers stresses caused by lattice expansion and contraction, enabling the device to maintain a current retention rate of 71.6% after 1,000 cycles. This study provides a universal strategy for designing high-performance electrochromic materials, advancing their practical applications in smart buildings and flexible displays.

π-conjugated polyimines in electrochromic devices with rapid response and good optical stability

Reversible metal electrodeposition (RME)-based electrochromic devices (ECDs) offer intriguing prospects for energy-saving buildings, information displays, military camouflage, etc. As the most crucial component of RME-based devices, the electrolyte governs the efficiency of ion transport and the reversibility of deposition/dissolution, thereby determining the optical modulation capability and service life of the devices. Herein, by tailoring the solvation structure, we developed a deep eutectic solvent (DES) electrolyte with high ionic conductivity (6.8-8.0 mS cm-1 at 25 °C), stable voltage window (∼2.7 V) and wide temperature range (-20 to 80 °C). Moreover, the DES-based electrolyte enables highly reversible Zn deposition and dissolution. The assembled RME-based device exhibits three optical states (transparent, colored, and mirror), a large average optical modulation of up to 87% across a broad wavelength range (400-800 nm), robust cycling stability (87.3% retention after 2400 cycles) and stable performance over a wide temperature range (-20 to 80 °C). Our work provides a new direction for the development of environmentally friendly, high-performance DES electrolytes and establishes a foundation for their application in RME-based devices.

Photodetectors play an essential role in optical communications, environmental monitoring, and medical imaging, and their performance strongly depends on the properties of the optoelectronic materials. Therefore, the exploration of high-performance optoelectronic materials has long been a research focus in the field of materials science. Viologen-based organic materials, owing to their unique redox and chromic characteristics, have been extensively utilized in electrochromic devices, biosensors, and flow batteries. In this work, a viologen complex containing the transition metal element Co, {[Co(BPYBDC) (H<sub>2</sub>O)5]·(BDC)·H<sub>2</sub>O} (denoted as 1-Co) was designed and successfully synthesized. A series of in-situ high-pressure characterization techniques were employed to systematically investigate its structural and optoelectronic behaviors. The results reveal that 1-Co crystallizes in the <i>Pc</i> space group and remains structurally stable up to 11.6 GPa without any phase transition. UV-visible absorption spectroscopy shows a red-shift of the absorption edge upon compression, accompanied by a color change from colorless and transparent to yellow, indicating a pressure-induced narrowing of the optical bandgap. Consistent with the bandgap narrowing, impedance measurements demonstrate a significant reduction in the total resistance under compression, which remains about two orders of magnitude lower than the initial value after decompression. Furthermore, the photocurrent response is markedly suppressed under compression and barely recovers upon pressure release. This behavior can be attributed to the enhanced recombination of electrons with viologen groups under compression, leading to the formation of stable viologen radical states. These localized radicals cannot effectively participate in the separation and transport of photogenerated carriers, thereby contributing little to the photocurrent. These findings suggest that high pressure effectively modulates the optical and electrical behaviors of 1-Co by tuning intermolecular interactions and the electronic band structure, providing valuable insights into the pressure-dependent behavior of viologen-based materials.

Crosslinking strategy effectively enhances stability of ProDOT-based electrochromic polymers and devices under extreme environmental conditions

Camouflage images corresponding to the four colors in an actual environment.

Self-powered flexible Zn-based electrochromic devices with viologen-based ionic porous organic polymer for adaptive camouflage

Silver-doped vanadium oxide electrochromic device by high-power impulse magnetron sputtering

Copolymers derived from 3-hexylthiophene and 3-methoxythiophene as potential active layers for polymeric electrochromic devices

Harnessing the spectrum: High-performance infrared electrochromic device with multicolor visibility based on PEDOT:PSS/SWCNT films

Novel quinoline-pyridine type viologens for near-infrared electrochromic devices

Synthesis and comprehensive evaluation of waste biomass-derived carbon dots as sustainable electrolytes for Vis-NIR modulation of electrochromic devices

In the present study, highly transparent evaporated tungsten oxide films with improved charge storage properties were used in battery-like (b-ECDs) and hybrid electrochromic devices (h-ECDs). A Co2+/3+ redox couple was added to the electrolyte as an alternative to other redox couples that have been already used in h-ECDs. The as-prepared h-ECDs, colored homogeneously, exhibited a contrast ratio of up to 7:1 in the visible spectrum, at a cathodic voltage of −2.5 V for only 10 s, compared to 3.5:1 at a cathodic voltage of −3 V for 180 s for a b-ECD. Moreover, when the redox couple was present in the electrolyte, almost a 50% higher areal capacitance and a 55% lower charge transfer resistance at the electrochromic layer/electrolyte interface were achieved. Also, the results show that the optical performance depends strongly on the coloration procedure (potentiostatic or galvanostatic), that self-bleaching is not so intense, and especially that the energy density consumed during bleaching is reduced in the presence of the redox couple. Overall, the findings of this study highlight the benefits of using a cobalt redox electrolyte in h-ECDs, allowing a direct comparison with b-ECDs, to dynamically control incoming solar irradiation in a building, thus improving buildings’ energy efficiency.

Abstract Electrochromic smart windows represent a promising technology for reducing building energy consumption through dynamic photo‐thermal regulation. However, scalable fabrication of high‐performance electrochromic films remains challenging. Herein, we pioneer slot‐die coating technique and aqueous inks for the high‐speed production (600 cm 2 /min) of Wadsley‐Roth structure TiNb 2 O 7 films. Experimental and theoretical analyses reveal that the open crystallographic shear channels in TiNb 2 O 7 enable efficient ion transport with a low diffusion barrier of 0.22 eV, allowing it to achieve a high diffusion coefficient (6.34 × 10 −10 cm 2 /s), good uniformity, and 82.8% large optical modulation at 600 nm. We constructed a series of large‐scale electrochromic devices with a size up to 200 cm 2 that demonstrate significant optical modulation (64.6%), rapid switching (23.4/12.4 s), and uniform coloration. We evaluated the photo‐thermal management performance of the device using a xenon lamp as a simulated solar source, achieving a notable temperature regulation of 18.8°C. To further validate its practical applicability, we conducted an outdoor test, demonstrating a temperature modulation of ∼5.0°C. Additionally, energy simulation analyses reveal that the device enables an energy saving of 155 MJ·m −2 . This work provides a scalable manufacturing strategy for high‐performance electrochromic devices, advancing the development of intelligent energy‐saving window technology.

Electrochromic devices enable dynamic modulation of light and heat, yet their broader adoption is hindered by limited color tunability, slow switching kinetics, and low coloration efficiency. Here, we present a complementary organic electrochromic device that addresses these challenges by employing dual conductive polymers: poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) and poly(benzodifurandione). The resulting device delivers exceptional performance, featuring a high optical contrast of 51% at 570 nm, ultrafast switching speeds (0.17/0.36 s for coloration/bleaching), a record-high coloration efficiency (1688 cm2 C⁻1 at 550 nm), and excellent cycling stability over 10,000 cycles. By integrating the device with a semitransparent organic solar cell, we realize a fully self-powered smart window with reducing indoor temperatures by 7 °C. Furthermore, coupling the electrochromic filter with a 4 × 4 organic photodetector array featuring on-chip Fabry–Pérot cavities enables a miniaturized spectrometer with 7.2 nm spectral resolution. This multifunctional electrochromic platform seamlessly bridges smart-window technology and spectral sensing, paving the way for energy-efficient, and compact optoelectronic systems.

To achieve high-performance electrochromism, one of the most critical challenge is how to attain a transparent state. For this purpose, we elaborately designed a diethylenetriamine-derived hexadentate nitrogen chelator functionalized with triphenylamine groups, which coordinates with manganese(II) ion to form an octahedral manganese(II) chelate. As d-d transition of the half-filled d5 manganese(II) center is forbidden, this manganese(II) chelate is colorless. Through electropolymerization of triphenylamine groups, we successfully fabricated a transparent metallopolymer film with manganese(II) chelates as repeating units. Under applied potentials, the initially transparent metallopolymer film undergoes stepwise oxidation at both manganese(II) and triphenylamine centers, so that the colorless film turns brown-yellow at 0.9V and further blue at 1.3V. The solid-state electrochromic device exhibits tricolor electrochromism from colorless to brownish yellow and blue at the voltages of 1.7 and 2.4V, respectively. The coloring/bleaching time, color contrast, and electrochromic efficiency are1.4s/0.4s, 40%, and 337.5 cm2C-1 between colorless and brownish yellow, whereas they become2.2s/0.4s, 73%, and 397.1 cm2C-1 between colorless and blue. The device exhibits excellent stability with up to 10 000 cycles for manganese-based electrochromism.

Abstract To achieve high‐performance electrochromism, one of the most critical challenge is how to attain a transparent state. For this purpose, we elaborately designed a diethylenetriamine‐derived hexadentate nitrogen chelator functionalized with triphenylamine groups, which coordinates with manganese(II) ion to form an octahedral manganese(II) chelate. As d–d transition of the half‐filled d 5 manganese(II) center is forbidden, this manganese(II) chelate is colorless. Through electropolymerization of triphenylamine groups, we successfully fabricated a transparent metallopolymer film with manganese(II) chelates as repeating units. Under applied potentials, the initially transparent metallopolymer film undergoes stepwise oxidation at both manganese(II) and triphenylamine centers, so that the colorless film turns brown‐yellow at 0.9 V and further blue at 1.3 V. The solid‐state electrochromic device exhibits tricolor electrochromism from colorless to brownish yellow and blue at the voltages of 1.7 and 2.4 V, respectively. The coloring/bleaching time, color contrast, and electrochromic efficiency are 1.4 s/0.4 s, 40%, and 337.5 cm 2 C −1 between colorless and brownish yellow, whereas they become 2.2 s/0.4 s, 73%, and 397.1 cm 2 C −1 between colorless and blue. The device exhibits excellent stability with up to 10 000 cycles for manganese‐based electrochromism.

Self-powered gas sensors based on zinc-air batteries (ZABs) integrate battery and gas sensing functions. Various gaseous reduction reactions at the battery cathode will induce a measurable and reproducible change in the battery's output voltage, eliminating the need for any external power supply. However, they still face significant challenges in achieving ultrasensitive, selective, and drift-resistant sensing under complex conditions. Herein, we report a NO2 gas sensor based on a ZAB, utilizing Fe-doped nickel phosphide (FNP) as the gas-sensitive material and incorporating deep learning algorithms to enhance the sensing performance. In the context of FNP gas-sensitive layers, the charge carrier mobility is significantly enhanced, owing to the electron delocalization and redistribution induced by the Fe dopants. Furthermore, the shift in the d-band center toward the Fermi level induced by Fe dopants facilitates stronger O 2p/Fe d orbital hybridization. As a result, the adsorbate-substrate interaction is enhanced and the Gibbs free energy of the NO2 reduction reaction is reduced. The charge density difference also indicates the facilitated electron transfer from FNP to NO2 and the electron accumulation at the O sites. Consequently, the sensors exhibit a high response (0.22 V @ 20 ppm), a low limit of detection (LOD: 61.8 ppb), and fast sensing speed (14 s). After that, the introduction of the InceptionTime model and wavelet transformation algorithm enables the sensor to achieve remarkable gas recognition and concentration quantification, along with a significantly reduced LOD of 36.9 ppb. Finally, a smart sensing device is constructed with the sensors, microcontrollers, and electrochromic devices for remote and visualized gas detections.

We present the synthesis and characterization of a viologen-based molten poly(ionic liquid), VPIL(TFSI), and its application to electrochromic (EC) devices. VPIL(TFSI) was obtained as a highly viscous liquid with a glass transition temperature of −23 °C, enabling its use in a molten state without additional solvent. Electrochemical analysis by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of neat VPIL(TFSI) revealed a unique conduction mechanism: while ionic conductivity is dominated by the counter-anion (TFSI) migration, charge transport during redox cycling involves electron hopping between viologen units. Diffusion coefficient analysis indicated that electron hopping is slower than counter-anion migration, suggesting that the reorientation of viologen moieties, rather than ion migration, determines the transport kinetics. An EC device was fabricated using an equimolar mixture of VPIL(TFSI) and a ferrocene-based RAIL as cathodic and anodic components, respectively, without any supporting electrolyte. The device exhibited distinct coloration with strong absorption bands at 530 and 890 nm, attributed to π-dimerization of reduced viologen species, along with high contrast and coloration efficiency comparable to theoretical values. These findings demonstrate the potential of molten poly(ionic liquids) as promising redox-active media for solvent-free and durable electrochromic devices.