Sheng-Yuan Kao

Planar Heterojunction Perovskite Solar Cells Incorporating Metal–Organic Framework Nanocrystals

Zr-based porphyrin metal-organic framework (MOF-525) nanocrystals with a crystal size of about 140 nm are synthesized and incorporated into perovskite solar cells. The morphology and crystallinity of the perovskite thin film are enhanced since the micropores of MOF-525 allow the crystallization of perovskite to occur inside; this observation results in a higher cell efficiency of the obtained MOF/perovskite solar cell.

Printed Multicolor High-Contrast Electrochromic Devices

In this study, electrochemical responses of inkjet-printed multicolored electrochromic devices (ECD) were studied to evaluate the feasibility of presenting multiple colors in one ECD. Metallo-supramolecular polymers (MEPE) solutions with two primary colors were inkjet-printed on flexible electrodes. By digitally controlling print dosages of each species, the colors of the printed EC thin film patterns can be adjusted directly without premixing or synthesizing new materials. The printed EC thin films were then laminated with a solid transparent thin film electrolyte and a transparent conductive thin film to form an ECD. After applying a dc voltage, the printed ECDs exhibited great contrast with a transmittance change (ΔT) of 40.1% and a high coloration efficiency of 445 cm(2) C(-1) within a short darkening time of 2 s. The flexible ECDs also showed the same darkening time of 2 s and still had a high ΔT of 30.1% under bending condition. This study demonstrated the feasibility to fabricate display devices with different color setups by an all-solution process and can be further extended to other types of displays.

Thermally Cured Dual Functional Viologen-Based All-in-One Electrochromic Devices with Panchromatic Modulation

Vinyl benzyl viologen (VBV) was synthesized and utilized to obtain all-in-one thermally cured electrochromic devices (ECDs). The vinyl moiety of VBV monomer could react with methyl methacrylate (MMA) to yield bulky VBV/poly(methyl methacrylate) (PMMA) chains and even cross-linked network without the assistance of additional cross-linker. Both the bulky VBV/PMMA chains and the resulting polymer network can hinder the aggregation of the viologens and reduce the possibility of dimerization, rendering enhanced cycling stability. Large transmittance changes (ΔT) over 60% at both 570 and 615 nm were achieved when the VBV-based ECD was switched from 0 V to a low potential bias of 0.5 V. Ultimately, the dual functional of VBV molecules, serving simultaneously as a promising electrochromic material and a cross-linker, is fully utilized in the proposed electrochromic system, making its fabrication process much easier. Negligible decays in ΔT at both wavelengths were observed for the cured ECD after being subjected to 1000 repetitive cycles, while 17.1% and 22.0% decays were noticed at 570 and 615 nm, respectively, for the noncured ECD. In addition, the low voltage-driven feature of the VBV-based ECD enables it to be incorporated with phenyl viologen (PV), further expanding the absorption range of the ECD. Panchromatic characteristic of the proposed PV/VBV-based ECD was demonstrated while exhibiting ΔT over 60% at both wavelengths. Only 5.3% and 6.9% decays, corresponding at 570 and 615 nm, respectively, were observed in the PV/VBV-based ECD after 10 000 continuous cycles at bleaching/coloring voltages of 0/0.5 V with an interval of 10 s for both bleaching and coloring processes.

Achieving a large contrast, low driving voltage, and high stability electrochromic device with a viologen chromophore

The viologen radical salt (VRS), consisting of phenyl viologen (PV) dications and 2,2,6,6-tetramethyl-1-piperidinyloxy derivative (TEMPOD) anions, was successfully synthesized. The VRS was combined with N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) to form an electrochromic device (ECD). This ECD offers significant transmittance changes (>60% at both 580 and 620 nm), but only requires 0.4 V for switching, the lowest driving voltage ever reported. Such a low driving voltage further strengthens the energy-saving capability of the ECD. The incorporation of TEMPOD in the ECD greatly improved its write–erase ability while insufficient bleaching was clearly observed within only 5 cycles in the case of its counterpart without adding TEMPOD anions. No significant decay in the transmittance change was noticed in the proposed ECD after subjecting to 100 cycles. Even better cycling stability would be expected if counter anions with multiple TEMPO units were utilized.

Water processable Prussian blue–polyaniline:polystyrene sulfonate nanocomposite (PB–PANI:PSS) for multi-color electrochromic applications

A new nanocomposite, Prussian blue–polyaniline:polystyrene sulfonate (PB–PANI:PSS), has been synthesized by incorporating both polyaniline (PANI) and Prussian blue (PB) electrochromic materials. The PB–PANI:PSS nanocomposite is synthesized by two-step polymerization, and the nanocomposite thin film is prepared by a wet-coating method on the conductive ITO glass. The PB–PANI:PSS thin film shows three optical states: highly transparent in a reduced state (−0.5 V vs. Ag/AgCl), green color at +0.2 V contributed by PANI, and blue-green color at +0.5 V contributed by both PANI and PB. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) mapping images show that the PB pigments were well dispersed in the PANI:PSS matrix. FTIR spectra show the specific absorbance peaks of both PANI:PSS and PB in the nanocomposite film. Cyclic voltammetry (CV) analysis reveals two redox pairs from the PB–PANI:PSS thin film. The UV-Vis absorbance spectra show a broader absorbance range for the nanocomposite than for pure PANI and PB. An averaged transmittance (Tave) was established to evaluate this wide-range absorbance material. The ΔTave value was 52.3% when applying an operation voltage between −0.5 and +0.5 V, and the switching times were 8.1 and 13.3 s for bleaching and darkening, respectively. The coloration efficiency was calculated to be 76.6 cm2 C−1 at the averaged visible wavelength. This PB–PANI:PSS composite thin film could potentially be useful for multi-color electrochromic applications because the ease of processing using water may facilitate the preparation of large-area thin films.

Enhanced Charge Collection in MOF-525–PEDOT Nanotube Composites Enable Highly Sensitive Biosensing

Abstract With the aim of a reliable biosensing exhibiting enhanced sensitivity and selectivity, this study demonstrates a dopamine (DA) sensor composed of conductive poly(3,4‐ethylenedioxythiophene) nanotubes (PEDOT NTs) conformally coated with porphyrin‐based metal–organic framework nanocrystals (MOF‐525). The MOF‐525 serves as an electrocatalytic surface, while the PEDOT NTs act as a charge collector to rapidly transport the electron from MOF nanocrystals. Bundles of these particles form a conductive interpenetrating network film that together: (i) improves charge transport pathways between the MOF‐525 regions and (ii) increases the electrochemical active sites of the film. The electrocatalytic response is measured by cyclic voltammetry and differential pulse voltammetry techniques, where the linear concentration range of DA detection is estimated to be 2 × 10−6–270 × 10−6 m and the detection limit is estimated to be 0.04 × 10−6 m with high selectivity toward DA. Additionally, a real‐time determination of DA released from living rat pheochromocytoma cells is realized. The combination of MOF5‐25 and PEDOT NTs creates a new generation of porous electrodes for highly efficient electrochemical biosensing.