In this Letter we report the plasmon-enhanced upconversion in single NaYF(4) nanocrystals codoped with Yb(3+)/Er(3+). Single nanocrystals and gold nanospheres are investigated and assembled in a combined confocal and atomic force microscope setup. The nanocrystals show strong upconversion emission in the green and red under excitation with a continuous wave laser in the near-infrared at 973 nm. By the use of the atomic force microscope, we couple single nanocrystals with gold spheres (30 and 60 nm in diameter) to obtain enhanced upconversion emission. An overall enhancement factor of 3.8 is reached. A comparison of time-resolved measurements on the bare nanocrystal and the coupled nanocrystal-gold sphere systems unveil that faster excitation as well as faster emission occurs in the nanocrystals.

With the aim of utilizing the infrared region of solar radiation to improve solar cell performance, significant progress, including theoretical analysis and experimental achievement, has been made in the field of up-conversion for photovoltaic applications. This Research News article reviews recent progress in the development of rear-earth (RE) ion doped up-conversion materials for solar cell applications. In addition, new trends for RE-ion-doped phosphors are briefly discussed, among them trivalent RE-ion-doped up-conversion materials for organic solar cell applications.

Three novel copolymers containing alternating 1,4-bis(phenylethenyl)benzene, 1,4-bis(phenylethenyl)-2,5dimethoxybenzene or 1,5-bis(phenylethenyl)naphthalene chromophores and crown ether (CE) spacers within the polymer backbone were synthesized by the Wittig polycondensation reaction. These copolymers exhibit good thermal stability (decomposition temperature around 380-411 uC). Photoluminescence (PL) and electroluminescence (EL) color can be easily tuned in these copolymers by simply changing the structure of the chromophores. Excimer emission is responsible for the changes in the PL spectra on going from solution to the thin films. Typical light-emitting electrochemical cell (LEC) behavior is observed in the EL devices with these copolymers as both electronic and ionic conductors. The turn-on voltage for emission is at 13.9 V, in forward bias, and at 24.4 V, under reverse bias. Efficient LECs with low turn-on voltages can be demonstrated upon addition of poly(ethylene oxide) (PEO) into the active layers. CE spacers in these copolymers contribute to the increasing ionic conductivity and the improvement in the morphology of the active layers. The d.c. response and a.c. impedance behaviors of the LECs with PEO were investigated, and the results indicate the operation of these LECs corresponds to the electrochemical doping mechanism.

2D transition metal carbides and nitrides (MXenes), a class of emerging nanomaterials with intriguing properties, have attracted significant attention in recent years. However, owing to the highly hydrophilic nature of MXene nanosheets, assembly strategies of MXene at liquid–liquid interfaces have been very limited and challenging. Herein, through the cooperative assembly of MXene and amine‐functionalized polyhedral oligomeric silsesquioxane at the oil–water interface, we report the formation, assembly, and jamming of a new type MXene‐based Janus‐like nanoparticle surfactants, termed MXene‐surfactants (MXSs), which can significantly enhance the interfacial activity of MXene nanosheets. More importantly, this simple assembly strategy opens a new platform for the fabrication of functional MXene assemblies from mesoscale (e.g., structured liquids) to macroscale (e.g., aerogels), that can be used for a range of applications, including nanocomposites, electronic devices, and all‐liquid microfluidic devices.

Solution-processed hybrid solar cells employing a low band-gap polymer and PbSx Se1-x alloy nanocrystals, achieving a record high PCE of 5.50% and an optimal FF of 67% are presented. The remarkable device efficiency can be attributed to the high-performance active materials, the optimal polymer/NCs ratio and, more importantly, the vertical donor/(donor:acceptor)/acceptor structure which benefits charge dissociation and transport.

Upconverting nanocrystals have a tremendous potential for applications in fields such as bioanalysis, medical therapy, or display technologies. However, a prerequisite for many applications is the availability of small, monodisperse, and highly luminescent nanocrystals. Here we show, that a microwave-assisted synthesis approach allows for the synthesis of such monodisperse and luminescent upconverting nanocrystals within 5 min in a closed reaction vessel. Even though the same reactants and solvents as with classical conductive heating reactions were used, microwave-assisted synthesis resulted in differently sized and shaped particles and provided superior reaction control. The nucleation and growth mechanism follows a La Mer scheme and can be controlled extremely accurately. It is expected that the fundamental principles of this synthesis approach can be applied to many other types of nanocrystals as well.

Four DÀA copolymers of tetradodecyl-substituted indacenodithiophene (IDT) donor unit with different acceptor units including bis(thiophen-2-yl)-bithiazole (BTz), bis(thiophen-2-yl)thiazolothiazole (TTz), bis(thiophen-2-yl)-tetrazine (TZ), and bis-(thiophen-2-yl)-benzothiadiazole (DTBT), PIDT-BTz, PIDT-TTz, PIDT-TZ, and PIDT-DTBT, were synthesized for the application as donor materials in polymer solar cells (PSCs). The copolymers possess good solubility benefitted from the four alkyl side chains on IDT unit, deeper HOMO levels at ca. À5.2 eV thanks to the IDT unit and tunable bandgap depending on the acceptor units. Among the copolymers, PIDT-TTz has the highest hole mobility (μ h ) of 4.99 Â 10 À3 cm 2 /V s. The power conversion efficiency (PCE) of the PSC based on PIDT-TTz/PC 70 BM (1:2 w/w) reached 5.79%, under the illumination of AM1.5G, 100 mW/ cm 2 . PIDT-DTBT film has the smallest bandgap of 1.68 eV and a higher μ h of 2.24 Â 10 À3 cm 2 /V s. The PSC based on PIDT-DTBT/PC 70 BM (1:3 w/w) exhibited an even higher PCE of 6.17% with a J sc of 13.27 mA/cm 2 , a V oc of 0.82 V, and a FF of 56.9%.

A series of conjugated donor (D)-π-acceptor (A) copolymers, P(BDT-F-BT), P(BDT-T-BT), and P(BDT-TT-BT), based on benzodithiophene (BDT) donor unit and benzothiadiazole (BT) acceptor unit with different π-bridges, were designed and synthesized via a Pd-catalyzed Stille-coupling method. The π-bridges between the BDT donor unit and BT acceptor unit are furan (F) in P(BDT-F-BT), thiophene (T) in P(BDT-T-BT) and thieno[3,2-b]thiophene (TT) in P(BDT-TT-BT). It was found that the π-bridges significantly affect the molecular architecture and optoelectronic properties of the copolymers. With the π-bridge varied from furan to thiophene, then to thieno[3,2-b]thiophene, the shape of the molecular chains changed from z-shaped to almost straight line gradually. Band gaps of P(BDT-F-BT), P(BDT-T-BT) and P(BDT-TT-BT) were tuned from 1.96 to 1.82 to 1.78 eV with HOMO levels up-shifted from −5.44 to −5.35 to −5.21 eV, respectively. Bulk heterojunction solar cells with the polymers as donor and PC71BM as acceptor demonstrated power conversion efficiency varied from 2.81% for P(BDT-F-BT) to 3.72% for P(BDT-T-BT) and to 4.93% for P(BDT-TT-BT). Compared to furan and thiophene, thieno[3,2-b]thiophene π-bridge in the copolymers shows superior photovoltaic performance. The results indicate that the photovoltaic performance of some high efficiency D–A copolymers reported in literatures could be improved further by inserting suitable π-bridges.