Dye-sensitized solar cells (DSSCs) have attracted significant attention as low-cost alternatives to conventional solid-state photovoltaic devices. [1][2][3] In these cells, the most successful chargetransfer sensitizers employed are ruthenium polypyridyl complexes, yielding 9-11% solar-to-electric power conversion efficiencies under AM 1.5. 4 The majority of the ruthenium complexes reported to date show absorption in the visible region at around 535 nm. Essential for efficient conversion of solar energy by DSSC is the spectral match of the sensitizer absorption to the solar radiation, and in this regard, the ruthenium complexes are inadequate. Therefore, development of sensitizers with extended absorption and spectral sensitivity into the infrared region is essential. Squaraines are well-known for their intense absorption in the red/near-IR regions, and for that reason, they are an excellent option to explore for solar cell applications. 5 Various groups have tested squaraines as sensitizers on wide band gap oxide semiconductors and obtained rather low power conversion efficiencies. [6][7][8][9][10] The reported low efficiencies of squaraines are due to aggregation and lack of directionality in the excited state. 11 There are several basic requirements guiding the molecular engineering of an efficient sensitizer. The excited-state redox potential should match the energy of the conduction band edge of the oxide. Light excitation should be associated with vectorial electron flow from the light-harvesting moiety of the sensitizer toward the semiconductor surface, providing for efficient electron transfer from the excited dye to the TiO 2 conduction band. Finally, a strong conjugation across the chromophore and anchoring groups is required for a good electronic coupling between the lowest unoccupied orbital (LUMO) of the dye and the TiO 2 conduction band. In order to satisfy these essential requirements, we have designed and developed a novel asymmetrical squaraine sensitizer that has a carboxylic acid group directly attached to the chromophore. In this paper, we report on the synthesis, electronic, and photovoltaic properties of the squaraine sensitizer. Scheme 1 shows the synthetic strategy used to obtain squaraine sensitizer (see Supporting Information for synthetic details). The UV/vis absorption spectrum (see Figure S1 in Supporting Information) of the squaraine sensitizer in ethanol shows an absorption maximum at 636 nm with high molar extinction coefficient ( ) 158 500 dm 3 mol -1 cm -1 ) corresponding to π-π* charge-transfer (CT) transitions. When the squaraine sensitizer is excited within the CT absorption band at room temperature in an air-equilibrated ethanol solution, it exhibits a strong luminescence maximum at 659 nm. The absorption spectrum of the squaraine sensitizer adsorbed on a 4 µm TiO 2 film shows features similar to those seen in the corresponding solution spectrum but exhibits a slight red shift of 15 nm due to the interaction of the anchoring group with the surface (see Figure S2 in Supportin...

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Lead sulfide (PbS) and cadmium sulfide (CdS) quantum dots (QDs) are prepared over mesoporous TiO2 films by a successive ionic layer adsorption and reaction (SILAR) process. These QDs are exploited as a sensitizer in solid‐state solar cells with 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) as a hole conductor. High‐resolution transmission electron microscopy (TEM) images reveal that PbS QDs of around 3 nm in size are distributed homogeneously over the TiO2 surface and are well separated from each other if prepared under common SILAR deposition conditions. The pore size of the TiO2 films and the deposition medium are found to be very critical in determining the overall performance of the solid‐state QD cells. By incorporating promising inorganic QDs (PbS) and an organic hole conductor spiro‐OMeTAD into the solid‐state cells, it is possible to attain an efficiency of over 1% for PbS‐sensitized solid‐state cells after some optimizations. The optimized deposition cycle of the SILAR process for PbS QDs has also been confirmed by transient spectroscopic studies on the hole generation of spiro‐OMeTAD. In addition, it is established that the PbS QD layer plays a role in mediating the interfacial recombination between the spiro‐OMeTAD+ cation and the TiO2 conduction band electron, and that the lifetime of these species can change by around 2 orders of magnitude by varying the number of SILAR cycles used. When a near infrared (NIR)‐absorbing zinc carboxyphthalocyanine dye (TT1) is added on top of the PbS‐sensitized electrode to obtain a panchromatic response, two signals from each component are observed, which results in an improved efficiency. In particular, when a CdS‐sensitized electrode is first prepared, and then co‐sensitized with a squarine dye (SQ1), the resulting color change is clearly an addition of each component and the overall efficiencies are also added in a more synergistic way than those in PbS/TT1‐modified cells because of favorable charge‐transfer energetics.

Designing lightweight nanostructured aerogels for high‐performance electromagnetic interference (EMI) shielding is crucial yet challenging. Ultrathin cellulose nanofibrils (CNFs) are employed for assisting in building ultralow‐density, robust, and highly flexible transition metal carbides and nitrides (MXenes) aerogels with oriented biomimetic cell walls. A significant influence of the angles between oriented cell walls and the incident EM wave electric field direction on the EMI shielding performance is revealed, providing an intriguing microstructure design strategy. MXene “bricks” bonded by CNF “mortars” of the nacre‐like cell walls induce high mechanical strength, electrical conductivity, and interfacial polarization, yielding the resultant MXene/CNF aerogels an ultrahigh EMI shielding performance. The EMI shielding effectiveness (SE) of the aerogels reaches 74.6 or 35.5 dB at a density of merely 8.0 or 1.5 mg cm –3 , respectively. The normalized surface specific SE is up to 189 400 dB cm 2 g –1 , significantly exceeding that of other EMI shielding materials reported so far.

A novel method allowing rapid production of reliable composites with increased dielectric constant and high dielectric strength for dielectric elastomer actuators (DEA) is reported. The promising approach using composites of conductive particles and insulating polymers generally suffers from low breakdown fields when applied to DEA devices. The present publication shows how to overcome this deficiency by using conductive polyaniline (PANI) particles encapsulated into an insulating polymer shell prior to dispersion. PANI particles are encapsulated using miniemulsion polymerization (MP) of divinylbenzene (DVB). The encapsulation process is scaled up to approximately 20 g particles per batch. The resulting particles are used as high dielectric constant (ϵ′) fillers. Composites in a polydimethylsiloxane (PDMS) matrix are prepared and the resulting films characterized by dielectric spectroscopy and tensile tests, and evaluated in electromechanical actuators. The composite films show a more than threefold increase in ϵ′, breakdown field strengths above 50 V μm−1, and increased strain at break. These novel materials allow tuning the actuation strain or stress output and have potential as materials for energy harvesting.

An optimized unsymmetrical squaraine dye 5‐carboxy‐2‐[[3‐[(2,3‐dihydro‐1, 1‐dimethyl‐3‐ethyl‐1H‐benzo[e]indol‐2‐ylidene)methyl]‐2‐hydroxy‐4‐oxo‐2‐cyclobuten‐1‐ylidene]methyl]‐3,3‐dimethyl‐1‐octyl‐3H‐indolium (SQ02) with carboxylic acid as anchoring group is synthesized for dye‐sensitized solar cells (DSCs). Although the π‐framework of SQ02 is insignificantly extended compared to its antecessor squaraine dye SQ01, photophysical measurements show that the new sensitizer has a much higher overall conversion efficiency η of 5.40% which is improved by 20% when compared to SQ01. UV‐vis spectroscopy, cyclic voltammetry and time dependent density functional theory calculations are accomplished to rationalize the higher conversion efficiency of SQ02. A smaller optical band gap including a higher molar absorption coefficient leads to improved light harvesting of the solar cell and a broadened photocurrent spectrum. Furthermore, all excited state orbitals relevant for the π–π* transition in SQ02 are delocalized over the carboxylic acid anchoring group, ensuring a strong electronic coupling to the conduction band of TiO2 and hence a fast electron transfer.

Printed functional conductive inks have triggered scalable production of smart electronics such as energy‐storage devices, antennas, wearable electronics, etc. Of particular interest are highly conductive‐additive‐free inks devoid of costly postdeposition treatments to eliminate sacrificial components. Due to the high filler concentration required, formulation of such waste‐free inks has proven quite challenging. Here, additive‐free, 2D titanium carbide MXene aqueous inks with appropriate rheological properties for scalable screen printing are demonstrated. Importantly, the inks consist essentially of the sediments of unetched precursor and multilayered MXene, which are usually discarded after delamination. Screen‐printed structures are presented on paper with high resolution and spatial uniformity, including micro‐supercapacitors, conductive tracks, integrated circuit paths, and others. It is revealed that the delaminated nanosheets among the layered particles function as efficient conductive binders, maintaining the mechanical integrity and thus the metallic conductive network. The areal capacitance (158 mF cm−2) and energy density (1.64 µWh cm−2) of the printed micro‐supercapacitors are much superior to other devices based on MXene or graphene. The ink formulation strategy of “turning trash into treasure” for screen printing highlights the potential of waste‐free MXene sediment printing for scalable and sustainable production of next‐generation wearable smart electronics.

A family of 2D transition metal carbides and nitrides known as MXenes has received increasing attention since the discovery of Ti3C2 in 2011. To date, about 30 different MXenes with well‐defined structures and properties have been synthesized, and many more are theoretically predicted to exist. Due to the numerous assets including excellent mechanical properties, metallic conductivity, unique in‐plane anisotropic structure, tunable band gap, and so on, MXenes rapidly positioned themselves at the forefront of the 2D materials world and have found numerous promising applications. Particular interest is devoted to applications in electrochemical energy storage, whereby 2D MXenes work either as electrodes, additives, separators, or hosts. This review summarizes recent advances in the synthesis, fundamental properties and composites of MXene and highlights the state‐of‐the‐art electrochemical performance of MXene‐based electrodes/devices. The progresses in the field of supercapacitors and Li‐ion batteries, Li‐S batteries, Na‐ and other alkali metal ion batteries are reviewed, and current challenges and new opportunities for MXenes in this surging energy storage field are presented. In the focus of interest is the possibility to boost device‐level performance, particularly that of rechargeable batteries, which are of utmost importance in future energy technologies. Very recently, the 2019 Nobel Prize in Chemistry was awarded to the inventors of the Li‐ion battery. For sure, this will provide an additional stimulation to study fundamental aspects of electrochemical energy storage.