Preparation and electrochromic properties of flexible transparent WO3/AgNWs decorated nanofiber composite film

It is well-known that tungsten oxide (WO3) is extensively used for electrochromic (EC) devices due to their special properties such as high coloration/bleaching response time, good coloration efficiency and so on. The preparation of flexible EC devices is highly desirable for various applications. However, the fabrication of flexible EC devices with improved performance is still major task due to their limited experimental protocols. In this work, we have prepared thr highly flexible transparent films consisting of WO3 and silver nanowires coated on nanofiber-reinforced composite films (WO3/AgNWs-NCF). The novel flexible transparent WO3/AgNWs-NCF is used for the electrochromic (EC) applications. The as-fabricated EC device based on WO3/AgNWs-NCF demonstrated a good coloration efficiency (161.3 cm2/C), excellent stability (81.5 %), and rapid respone time for coloration (2.9 sec) and bleaching (3.2 sec). The fabricated transparent flexible EC device may be potentially useful to design an outstanding EC device for a smart window application.

Modifying Precursor Solutions to Obtain Screen-Printable Inks for Tungsten Oxides Electrochromic Film Preparation

Tungsten trioxide (WO3) is used to prepare the important electrochromic layer of the electrochromic device as a wide bandgap semiconductor material. In this study, WO3 electrochromic film was successfully prepared by screen printing. To modify the thixotropy and wettability of the ink, polyvinyl alcohol (PVA) and 2-perfluoroalkyl ethanol (FSO) were added in the ammonium meta-tungstate (AMT) solution. We found that the PVA additive could improve the dynamic viscosity of the solution and modify the uniformity of the film. 2-Perfluoroalkyl ethanol (FSO) could lower the surface tension and increase the wettability of the AMT solution on the substrate. By observing the morphology of the printed films, the ink formulas for screen printing were selected. We found the annealing process could help remove PVA. Through characterization of electrochromic performance, it was found that the best performing device had 42.57% modulation and 93.25 cm2·C−1 coloration efficiency (CE) for 600 nm light. This study showed great potential in the preparation of WO3 electrochromic devices by a low-cost screen-printing method.

A Mini-Review: Pyridyl-Based Coordination Polymers for Energy Efficient Electrochromic Application

Electrochromic devices (ECDs) have a broad range of application prospects in many important energy efficient optoelectronic fields, such as smart windows, anti-glare rearview mirrors, low-energy displays, and infrared camouflage. However, there are some factors restricting their development, such as low coloration efficiency, slow switching speed, and poor cycling stability. Coordination polymer (CP) is a promising active material for the fabrication of high-performance ECD because of its ultrahigh coloration efficiency, fast switching speed, and excellent cycling stability. In this review, current advances of CP in energy efficient ECDs are comprehensively summarized and evaluated. Specifically, the effects of composition, coordination bonding, and microstructure of the bipyridine- and terpyridine-based CP on EC performances are introduced and discussed in detail. Then, the challenges and prospects of this booming field are proposed. Finally, the broad application prospects of the CPs-based EC materials and the corresponding devices are also demonstrated, which hold numerous revolutionary effects over our daily life. Hopefully, this review would provide useful guidance and further promote progress on the electrochromic and other optoelectronic fields.

Electrodeposited Copolymers Based on 9,9′-(5-Bromo-1,3-Phenylene)Biscarbazole and Dithiophene Derivatives for High-Performance Electrochromic Devices

A 1,3-bis(carbazol-9-yl)benzene derivative (BPBC) was synthesized and its related homopolymer (PBPBC) and copolymers (P(BPBC-co-BT), P(BPBC-co-CDT), and P(BPBC-co-CDTK)) were prepared using electrochemical polymerization. Investigations of polymeric spectra showed that PBPBC film was grey, iron-grey, yellowish-grey, and greyish-green from the neutral to the oxidized state. P(BPBC-co-BT), P(BPBC-co-CDT), and P(BPBC-co-CDTK) films showed multicolor transitions from the reduced to the oxidized state. The transmittance change (DT) of PBPBC, P(BPBC-co-BT), P(BPBC-co-CDT), and P(BPBC-co-CDTK) films were 29.6% at 1040 nm, 44.4% at 1030 nm, 22.3% at 1050 nm, and 41.4% at 1070 nm. The coloration efficiency (η) of PBPBC and P(BPBC-co-CDTK) films were evaluated to be 140.3 cm2 C−1 at 1040 nm and 283.7 cm2 C−1 at 1070 nm, respectively. A P(BPBC-co-BT)/PEDOT electrochromic device (ECD) showed a large DT (36.2% at 625 nm) and a fast response time (less than 0.5 s), whereas a P(BPBC-co-CDTK)/PEDOT ECD revealed a large η (534.4 cm2 C–1 at 610 nm) and sufficient optical circuit memory.

Dual-Cation Electrolytes Crosslinked with MXene for High-Performance Electrochromic Devices

MXene, a 2D material, is used as a filler to manufacture polymer electrolytes with high ionic conductivity because of its unique sheet shape, large specific surface area and high aspect ratio. Because MXene has numerous -OH groups on its surface, it can cause dehydration and condensation reactions with poly(4-styrenesulfonic acid) (PSSA) and consequently create pathways for the conduction of cations. The movement of Grotthuss-type hydrogen ions along the cation-conduction pathway is promoted and a high ionic conductivity can be obtained. In addition, when electrolytes composed of a conventional acid or metal salt alone is applied to an electrochromic device (ECD), it does not bring out fast response time, high coloration efficiency and transmittance contrast simultaneously. Therefore, dual-cation electrolytes are designed for high-performance ECDs. Bis(trifluoromethylsulfonyl)amine lithium salt (LiTFSI) was used as a source of lithium ions and PSSA crosslinked with MXene was used as a source of protons. Dual-Cation electrolytes crosslinked with MXene was applied to an indium tin oxide-free, all-solution-processable ECD. The effect of applying the electrolyte to the device was verified in terms of response time, coloration efficiency and transmittance contrast. The ECD with a size of 5 × 5 cm2 showed a high transmittance contrast of 66.7%, fast response time (8 s/15 s) and high coloration efficiency of 340.6 cm2/C.