New Pyridinium Ylide Dyes for Dye Sensitized Solar Cell Applications

Novel organic pyridinium ylide sensitizers (NO109–111) consisting of various anchoring groups were synthesized and characterized for applications in dye sensitized solar cells. Compared with the pyridine-<i>N</i>-oxide dye (NO108), the ylide sensitizers with strong electron-withdrawing acceptors exhibited dominant ultraviolet absorption properties and efficient binding abilities to the TiO₂ surface. Among these dyes, the pyridinium ylide NO111 sensitized solar cell showed the highest efficiency (5.15%), which was improved to 7.41% by employing coadsorbent chenodeoxycholic acid

Probing Eu²⁺ Luminescence from Different Crystallographic Sites in Ca₁₀M(PO₄)₇:Eu²⁺ (M = Li, Na, and K) with β‑Ca₃(PO₄)₂‑Type Structure

Eu²⁺ local environments in various crystallographic sites enable the different distributions of the emission and excitation energies and then realize the photoluminescence tuning of the Eu²⁺ doped solid state phosphors. Herein we report the Eu²⁺-doped Ca₁₀M­(PO₄)₇ (M = Li, Na, and K) phosphors with β-Ca₃(PO₄)₂-type structure, in which there are five cation crystallographic sites, and the phosphors show a color tuning from bluish-violet to blue and yellow with the variation of M ions. The difference in decay rate monitored at selected wavelengths is related to multiple luminescent centers in Ca₁₀M­(PO₄)₇:Eu²⁺, and the occupied rates of Eu²⁺ in Ca(1), Ca(2), Ca(3), Na(4), and Ca(5) sites from Rietveld refinements using synchrotron power diffraction data confirm that Eu²⁺ enters into four cation sites except for Ca(5). Since the average bond lengths <i>d</i>(Ca–O) remain invariable in the Ca₁₀M­(PO₄)₇:Eu²⁺, the drastic changes of bond lengths <i>d</i>(M–O) and Eu²⁺ emission depending on the variation from Li to Na and K can provide insight into the distribution of Eu²⁺ ions. It is found that the emission band at 410 nm is ascribed to the occupation of Eu²⁺ in the Ca(1), Ca(2), and Ca(3) sites with similar local environments, while the long-wavelength band (466 or 511 nm) is attributed to Eu²⁺ at the M(4) site (M = Na and K). We show that the crystal-site engineering approach discussed herein can be applied to probe the luminescence of the dopants and provide a new method for photoluminescence tuning

Water-Resistant Efficient Stretchable Perovskite-Embedded Fiber Membranes for Light-Emitting Diodes

Cesium lead halide perovskite nanocrystals (NCs) with excellent intrinsic properties have been employed universally in optoelectronic applications but undergo hydrolysis even when exposed to atmospheric moisture. In the present study, composite CsPbX₃ (X = Cl, Br, and I) perovskite NCs were encapsulated with stretchable (poly­(styrene-butadiene-styrene); SBS) fibers by electrospinning to prepare water-resistant hybrid membranes as multicolor optical active layers. Brightly luminescent and color-tunable hydrophobic fiber membranes (FMs) with perovskite NCs were maintained for longer than 1 h in water. A unique remote FMs packaging approach was used in high-brightness perovskite light-emitting diodes (PeLEDs) for the first time

Side Group of Poly(3-alkylthiophene)s Controlled Dispersion of Single-Walled Carbon Nanotubes for Transparent Conducting Film

Controlled dispersion of single-walled carbon nanotubes (SWCNTs) in common solvents is a challenging issue, especially for the rising need of low cost flexible transparent conducting films (TCFs). Utilizing conductive polymer as surfactant to facilitate SWCNTs solubility is the most successful pragmatic approach to such problem. Here, we show that dispersion of SWCNT with polymer significantly relies on the length of polymer side groups, which not only influences the diameter distribution of SWCNTs in solution, also eventually affects their effective TCF performance. Surfactants with longer side groups covering larger nanotube surface area could induce adequate steric effect to stabilize the wrapped SWCNTs against the nonspecific aggregation, as discerned by the optical and microscopic measurements, also evidenced from the resultant higher electrokinetic potential. This approach demonstrates a facile route to fabricate large-area SWCNTs-TCFs exhibiting high transmittance and high conductivity, with considerable uniformity over 10 cm × 10 cm

Effect of Extended Conjugation of N‑Heterocyclic Carbene-Based Sensitizers on the Performance of Dye-Sensitized Solar Cells

We report the synthesis, characterization, and photovoltaic properties of four ruthenium complexes (<b>CI101</b>, <b>CBTR</b>, <b>CB111</b>, and <b>CB108</b>) having various N-heterocyclic carbene ancillary ligands, pyridine-imidazole, -benzimidazole, -dithienobenzimidazole, and -phenanthroimidazole, respectively. These complexes were designed to investigate the effect of extended conjugation ordained from ring fusion on the power conversion efficiencies of the solar cells. The device sensitized by <b>CB108</b>, the pyridine-phenanthroimidazole conjugated complex, showed an improved efficiency (9.89%) compared to those of pyridine-benzimidazole conjugated system (<b>CBTR</b>, 9.72%) and the parent unfused ring system (<b>CI101</b>, 6.24%). Surprisingly, the sulfur-incorporated pyridine-dithienobenzimidazole system (<b>CB111</b>, 9.24%) exhibited a little lower efficiency than that of <b>N719</b> (9.41%). The enhanced photovoltaic performance of <b>CB108</b> was mainly attributed to the increase in electron lifetime and diffusion length confirmed by the electrochemical impedance spectroscopy

Highly Efficient Blue Emission and Superior Thermal Stability of BaAl₁₂O₁₉:Eu²⁺ Phosphors Based on Highly Symmetric Crystal Structure

Highly efficient phosphor materials with superior thermal stability are indispensable for phosphor-converted white light-emitting diodes (pc-WLEDs) solid state lighting. In order to obtain a high quality warm white light, near-ultraviolet (n-UV) chips combined with trichromatic phosphors have be extensively studied. Among them, the development of efficient blue phosphor remains a challenging task. In view of the close correlation between 5d–4f transitions of rare earth ions and the coordination environment of host lattice, many studies have been dedicated to improving the photoluminescence performances by modifying the lattice coordination environment including the lattice rigidity and symmetry. In this work, we reported highly efficient blue-emitting Eu²⁺-doped BaAl₁₂O₁₉ (BAO) phosphors with excellent thermal stability, which were prepared via the traditional high-temperature solid state reaction routes. According to the X-ray powder diffraction (XRD) Rietveld refinement analysis, BAO owned a highly symmetric layer structure with two Ba polyhedrons, marked as Ba(1)­O₉ and Ba(2)­O₁₀, respectively. The diffuse reflectance spectra revealed the optical band gap to be 4.07 eV. Due to the suitable optical bandgap, the Eu²⁺ ions could realize a highly efficient doping in the BAO matrix. The photoluminescence excitation (PLE) spectra for as-prepared BAO:Eu²⁺ phosphors exhibited a broad absorption band in the region from 250 to 430 nm, matching well with the n-UV LED chip. Under the UV radiation, it is highly luminous (internal quantum yields (IQYs) = 90%) with the peak around 443 nm. Furthermore, the color purity of BAO:Eu²⁺ phosphors could achieve 92%, ascribing to the narrow full width at half-maximum (fwhm = 52 nm), which was even much better than that of commercially available BAM:Eu²⁺ phosphor (color purity = 91.34%, fwhm = 51.7 nm). More importantly, the as-prepared BAO:Eu²⁺ phosphor showed extra high thermal stability when working in the region of 298–550 K, which was a bit better than that of commercial BAM:Eu²⁺ phosphors. According to the distortion calculation of Ba crystallographic occupation, the superior thermal stability could be attributed to the highly symmetric crystal structure of BAO host. In view of the excellent luminescence performances of BAO:Eu²⁺, it is a promising blue-emitting phosphor for n-UV WLED