The spontaneous zwitterionic copolymerization (SZWIP) of 2-oxazolines and acrylic acid affords biocompatible but low molecular weight linear N-acylated poly(amino ester)s (NPAEs). Here, we present a facile one-step approach to prepare functional higher molar mass cross-linked NPAEs using 2,2′-bis(2-oxazoline)s (BOx). In the absence of solvent, insoluble free-standing gels were formed from BOx with different length n-alkyl bridging units, which when butylene-bridged BOx was used possessed an inherent green fluorescence, a behavior not previously observed for 2-oxazoline-based polymeric materials. We propose that this surprising polymerization-induced emission can be classified as nontraditional intrinsic luminescence. Solution phase and oil-in-oil emulsion approaches were investigated as means to prepare solution processable fluorescent NPAEs, with both resulting in water dispersible network polymers. The emulsion-derived system was investigated further, revealing pH-responsive intensity of emission and excellent photostability. Residual vinyl groups were shown to be available for modifications without affecting the intrinsic fluorescence. Finally, these systems were shown to be cytocompatible and to function as fluorescent bioimaging agents for in vitro imaging.
High-quality and millimeter-sized perovskite single crystals of CsPbBr3 and Cs4PbBr6 were prepared in organic solvents and studied for correlation between photocurrent generation and photoluminescence (PL) emission. The CsPbBr3 crystals, which have a 3D perovskite structure, showed a highly sensitive photoresponse and poor PL signal. In contrast, Cs4PbBr6 crystals, which have a 0D perovskite structure, exhibited more than 1 order of magnitude higher PL intensity than CsPbBr3, which generated an ultralow photoresponse under illumination. Their contrasting optoelectrical characteristics were attributed to different exciton binding energies, induced by coordination geometry of the [PbBr6]4– octahedron sublattices. This work correlated the local structures of lead in the primitive perovskite and its derivatives to PL spectra as well as photoconductivity.
Color-conversion films (CCFs) were fabricated with CuInS2/ZnS quantum dot (QD)-embedded polymer nanofibers and applied for white color emission with blue light-emitting diodes (LEDs).
Evolution of the long-term (400 h) thermal stability of green CdSe@ZnS alloyed core/shell QDs (A-QDs) and CdSe@ZnS/ZnS (alloyed core/shell)/thick shell QDs (AS-QDs) under 85 °C, 85% relative humidity conditions in air.
CdSe/ZnS quantum dots (QDs) were incorporated into biocompatible polyisoprene (PI) particles by microencapsulation through emulsification/solvent evaporation, a technique that is facile, robust, and inexpensive. Emulsification/solvent evaporation results in QDs encapsulated into the particle core without requiring chemical modification of the as-prepared QDs. The PI can be easily cross-linked after encapsulation to enhance the fluorescence stability of the QDs. The resulting PI−QD nanocomposite particles form as colloidally stable suspensions in water that exhibit stable fluorescence for months. The surface of the PI−QD nanocomposite particles was functionalized with carboxylates during the QD encapsulation to facilitate subsequent bioconjugation. Streptavidin-coated PI−QD particles displayed selective binding to biotin-conjugated polystyrene spheres, thus demonstrating the potential application of these particles in biolabeling.
Scientific Reports 6: Article number: 35994; published online: 27 October 2016; updated: 16 March 2017. Ujwal Thakur was omitted from the author list in the original version of this Article. This has been corrected in the PDF and HTML versions of the Article, as well as the Supplementary Informationfile.
The ligand assisted reprecipitation (LARP) technique is an accessible and facile method that can synthesize metal halide perovskite nanocrystals (PNCs) under ambient conditions. However, low product yields of less than 30% for LARP and its contemporary methods are indicative of highly inefficient reactions. In this work we apply the principles of green chemistry to the LARP technique for synthesizing CsPbBr3 PNCs and help address this issue. Through these efforts, high product yields of ∼70% are achieved using stochiometric Cs : Pb precursor ratios. This is realized by (i) substituting the conventional toluene (TOL) anti-solvent with ethyl acetate (EA) and (ii) replacing the conventionally used unsaturated oleylamine ligand with the shorter saturated octylamine ligand. These changes also result in a 60% molar reduction in total ligand concentration and a 62.5% reduction in solvent waste during purification. The synthesized PNCs are comparable to the TOL-LARP reference in crystal quality, morphology and phase, with their photoluminescence quantum yields being readily enhanced to over 80% through additions of RNH3Br ligands. The spectral versatility of these materials is demonstrated through post-synthetic chloride and iodide halide anion exchange, which readily yields tunable CsPbX3 derivatives across the visible spectrum. Our EA-LARP protocol is further shown to be readily upscaled to ∼0.5 L, while maintaining good nanocrystal properties and a product yield of 60%.
Currently, the most efficient perovskite solar cells (PSCs) mainly use planar and mesoporous titanium dioxide (TiO2) as an electron-transport layer (ETL). However, because of its intrinsic photocatalytic properties, TiO2 can decompose perovskite absorber and lead to poor stability under solar illumination (ultraviolet light). Herein, a simplified architectural ETL-free PSC with enhanced efficiency and outstanding photostability is produced by the facile deposition of a bathocuproine (BCP) interlayer. Power conversion efficiency of the ETL-free PSC improves from 15.56 to 19.07% after inserting the BCP layer, which is the highest efficiency reported for PSCs involving an ETL-free architecture, versus 19.03% for the n–i–p full device using TiO2 as an ETL. The BCP interlayer has been demonstrated to have several positive effects on the photovoltaic performances of devices, such as "modulation doping" of the perovskite layer, modification of FTO surface work function, and enhancing the charge-transfer efficiency between FTO and perovskite. Moreover, the BCP-based ETL-free devices exhibit outstanding photostability: the unencapsulated BCP-based ETL-free PSCs retain over 90% of their initial efficiencies after 1000 h of storage in air and maintain 92.2% after 450 h of exposure to full solar irradiation (without a UV filter), compared to only 14.1% in the n–i–p full cells under the same condition.
Abstract In CH 3 NH 3 PbI 3 -based high efficiency perovskite solar cells (PSCs), tiny amount of PbI 2 impurity was often found with the perovskite crystal. However, for two-step solution process-based perovskite films, most of findings have been based on the films having different morphologies between with and without PbI 2 . This was mainly due to the inferior morphology of pure perovskite film without PbI 2 , inevitably produced when the remaining PbI 2 forced to be converted to perovskite, so advantages of pure perovskite photoactive layer without PbI 2 impurity have been overlooked. In this work, we designed a printing-based two-step process, which could not only generate pure perovskite crystal without PbI 2 , but also provide uniform and full surface coverage perovskite film, of which nanoscale morphology was comparable to that prepared by conventional two-step solution process having residual PbI 2 . Our results showed that, in two-step solution process-based PSC, pure perovskite had better photon absorption and longer carrier lifetime, leading to superior photocurrent generation with higher power conversion efficiency. Furthermore, this process was further applicable to prepare mixed phase pure perovskite crystal without PbI 2 impurity, and we showed that the additional merits such as extended absorption to longer wavelength, increased carrier lifetime and reduced carrier recombination could be secured.
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