Electrochromic and colorimetric properties of anodic NiO thin films: Uncovering electrochromic mechanism of NiO

D-A Structural Oligomers Containing Benzothiadiazole or Benzophenone as Novel Multifunctional Materials for Electrochromic and Photodetector Devices

In this study, six conjugated oligomers containing D-A structures were synthesized using the Stille coupling reaction and named PHZ1-PHZ6. All the oligomers utilized demonstrated excellent solubilities in common solvents and notable color variations in the domain of electrochromic characteristics. By designing and synthesizing two electron-donating groups modified with alkyl side chains and a common aromatic electron-donating group, as well as cross-binding them with two electron-withdrawing groups with lower molecular weights, the six oligomers presented good color-rendering efficiencies, among which PHZ4 presented the best color-rendering efficiency (283 cm²·C^-1). The products also demonstrated excellent electrochemical switching-response times. PHZ5 presented the fastest coloring time (0.7 s), PHZ3 and PHZ6 presented the fastest bleaching times (2.1 s). Following 400 s of cycling activity, all the oligomers under study showed good working stabilities. Moreover, three kinds of photodetectors based on conducting oligomers were prepared, and the experimental results show that the three photodetectors have better specific detection performances and gains. These characteristics indicate that oligomers containing D-A structures are suitable for use as electrochromic and photodetector materials in the research.

Enhanced Electrochromic Performance of All-Solid-State Electrochromic Device Based on W-Doped NiO Films

Electrochromic materials have attracted much attention due to their promising applications in smart windows and thermal control. However, NiO is a weak point for a complementary ECD and needs to be improved due to its low optical modulation and charge density. In this work, the W-doped NiO films are designed and prepared by RF magnetron co-sputtering to improve the performance of the NiO. The results shows that the optical modulation of the W-NiO (52.7%) is significantly improved compared with pure NiO (33.8%), which can be assigned to the increase in lattice boundaries due to the W doping. The response time of W-NiO is 8.8 s for coloring and 7.2 s for bleaching, which is similar to that of NiO film. The all-solid-state electrochromic devices (ECDs) that employed W-NiO as a complementary layer are prepared and exhibit a high-transmittance modulation of 48.5% in wavelengths of 450–850 nm and an emittance modulation of 0.28 in 2.5–25 μm, showing great application potential in the field of smart windows and spacecraft thermal control devices. The strategy of preparing NiO doped by W indicates an innovative direction to obtain ECDs with high performance.

Silver Nanowire-Based Printable Electrothermochromic Ink for Flexible Touch-Display Applications

Flexible, lightweight, low-power, and low-cost displays are an active area of interest in the electronics community. In this work, we have developed a composite electrothermochromic material consisting of silver nanowires (Ag NWs) and thermochromic powders, which exhibits reversible color (phase) change during biasing due to Joule heating. A wide variety of color combinations are possible with suitable thermochromic material selection. We have formulated this composite material as a printable ink so that patterned deposition can be achieved in a single step. A low processing temperature of 100 °C makes the composite compatible with a wide range of flexible substrates such as paper and polyethylene terephthalate (PET). The material (encapsulated with polydimethylsiloxane (PDMS)) exhibits good flexibility and is observed to be functional after 10 000 bending cycles with <7% resistance change. We have fabricated a low-power seven-segment color display to show the material's suitability for practical display applications. We have also demonstrated that the same layer can function as a display and as a touch sensor because of its conducting and chromatic properties without additional active layers on top. The material is suitable for the fabrication of low-cost, flexible touch color displays for interactive electronic readers, digital posters, and flexible digital signboards.

Colorimetric properties and structural evolution of cathodic electrochromic WO3 thin films

Cathodic amorphous tungsten trioxide (WO3) thin films have been deposited by reactive direct current magnetron sputtering and have been studied for their colorimetric and electrochromic properties. Those studies were carried out under two different potential cycling process: (i) switching mode (the response between coloration and bleaching in increasing potential steps) and (ii) modulation mode (the stepwise modulation to coloration with increasing potential and back to bleaching). Optical measurements, performed as a function of applied potential, showed excellent transmittance contrasts (∼80%) between colored and bleached states. The color stimuli and the changes that take place upon reversible switching or modulation were recorded based on the Commisson International de l’Éclairage (CIE) system. It was found that, under various potentials, significant changes occurred in the hue and saturation for WO3, as exhibited by the CIE 1931 xy chromaticity coordinates. As WO3 was reduced (W6+ + e– → W5+), a sharp decrease in luminance was observed. Excellent reversibility is demonstrated not only by colorimetric properties, but also by the corresponding intrinsic structures of the films, as investigated by µ-Raman spectroscopy. Furthermore, the WO3 films displayed a fast response time and good long-term cycling durability, which was attributed to their amorphous nature.

Revealing the Charge Storage Mechanism of Nickel Oxide Electrochromic Supercapacitors

Nickel oxide (NiO) is considered one of the most promising positive anode materials for electrochromic supercapacitors. Nevertheless, a detailed mechanism of the electrochromic and energy storage process has yet to be unraveled. In this research, the charge storage mechanism of a NiO electrochromic electrode was investigated by combining the in-depth experimental and theoretical analyses. Experimentally, a kinetic analysis of the Li-ion behavior based on the cyclic voltammetry curves reveals the major contribution of surface capacitance versus total capacity, providing fast reaction kinetics and a highly reversible electrochromic performance. Theoretically, our model uncovers that Li ions prefer to adsorb at fcc sites on the NiO(1 1 1) surface, then diffuse horizontally over the plane, and finally migrate in the bulk. More significantly, the calculated theoretical surface capacity (106 mA h g^-1) accounts for about 77.4% of the total experimental capacity (137 mA h g^-1), indicating that the surface storage process dominates the whole charge storage, which is in accordance with the experimental results. This work provides a fundamental understanding of transition-metal oxides for application in electrochromic supercapacitors and can also promote the exploration of novel electrode materials for high-performance electrochromic supercapacitors.