Strong CPL-active liquid crystal materials induced by intermolecular hydrogen-bonding interaction and a chirality induction mechanism.

A novel co-assembly material can emit strong CPL signals (λem = 485 nm, glum = +0.076/-0.064) from an achiral AIE-active ß-cyanostilbene (CYS) liquid crystal dye through intermolecular hydrogen bond (HB) interaction and chirality induction after a rapid cooling quench treatment.

Strong-Induced CPL Emission Promoted from Achiral Conjugated Polymer-Containing Emissive Nematic Liquid Crystals (P-N*-LCs).

With the rapid development on 3D printing technology, more and more works have been devoted to 3D display. 3D display will really come true by using circularly polarized luminescence (CPL)-active materials with both high quantum yield and dissymmetry factor (gem ) in organic light-emitting diode or liquid crystals (LCs). But so far most of these CPL materials cannot meet the real application requirement because of the low gem values in the range of 10-5 -10-2 . In this paper, ternary chiral emissive LCs (P-N*-LCs) is designed by doping chiral binaphthyl-based enantiomers as chiral dopant (Guest 1) and achiral conjugated polymer as induced CPL emitter (Guest 2) into nematic liquid crystal (N-LCs) Host 5CB. Both Guest 1 and Guest 2 show excellent compatibility with Host 5CB. The obtained ternary P-N*-LCs can emit strong-induced CPL signal with gem up to 1.12 and ФFL up to 66.1%. This work first develops a new strategy for the smart design of excellent CPL materials from versatile achiral conjugation fluorescence polymers.

All-Inorganic Perovskite Solar Cells.

The research field on perovskite solar cells (PSCs) is seeing frequent record breaking in the power conversion efficiency (PCE). However, organic-inorganic hybrid halide perovskites and organic additives in common hole-transport materials (HTMs) exhibit poor stability against moisture and heat. Here we report the successful fabrication of all-inorganic PSCs without any labile or expensive organic components. The entire fabrication process can be operated in ambient environment without humidity control (e.g., a glovebox). Even without encapsulation, the all-inorganic PSCs present no performance degradation in humid air (90-95% relative humidity, 25 °C) for over 3 months (2640 h) and can endure extreme temperatures (100 and -22 °C). Moreover, by elimination of expensive HTMs and noble-metal electrodes, the cost was significantly reduced. The highest PCE of the first-generation all-inorganic PSCs reached 6.7%. This study opens the door for next-generation PSCs with long-term stability under harsh conditions, making practical application of PSCs a real possibility.

Ultrafast photothermoelectric effect in Dirac semimetallic Cd3As2 revealed by terahertz emission.

The thermoelectric effects of topological semimetals have attracted tremendous research interest because many topological semimetals are excellent thermoelectric materials and thermoelectricity serves as one of their most important potential applications. In this work, we reveal the transient photothermoelectric response of Dirac semimetallic Cd3As2, namely the photo-Seebeck effect and photo-Nernst effect, by studying the terahertz (THz) emission from the transient photocurrent induced by these effects. Our excitation polarization and power dependence confirm that the observed THz emission is due to photothermoelectric effect instead of other nonlinear optical effect. Furthermore, when a weak magnetic field (~0.4 T) is applied, the response clearly indicates an order of magnitude enhancement on transient photothermoelectric current generation compared to the photo-Seebeck effect. Such enhancement supports an ambipolar transport nature of the photo-Nernst current generation in Cd3As2. These results highlight the enhancement of thermoelectric performance can be achieved in topological Dirac semimetals based on the Nernst effect, and our transient studies pave the way for thermoelectric devices applicable for high field circumstance when nonequilibrium state matters. The large THz emission due to highly efficient photothermoelectric conversion is comparable to conventional semiconductors through optical rectification and photo-Dember effect.

Controllable Circularly Polarized Electroluminescence Performance Improved by the Dihedral Angle of Chiral-Bridged Binaphthyl-Type Dopant Inducers.

Chirality of 1,1'-binaphthol (BINOL) is due to the restricted rotation between two naphthalene rings, and its skeletal structure of binaphthyl unit can be further modified by choosing functionalized substituents to afford the enlarged chiral induction effect. In this paper, we designed and synthesized nine chiral binaphthyl derivatives (R/S-1-R/S-9) as circularly polarized electroluminescence (CP-EL) inducers by inserting various bridged alkyl chains into the hydroxyl groups of BINOL or introducing functionalized substituents with different steric hindrances on the 3,3'-position of 2,2'-methylenedioxy-1,1'-binaphthalene. Their molecular conformations and CPL behaviors of nine chiral inducers were significantly dependent on the length of the alkyl chain and the degree of substituent steric hindrance, which could further regulate their chiral induction effect on achiral fluorescent polymer F8BT from small to large in the doped films. Moreover, in virtue of the planar rigid conjugated molecular conformation of R/S-1, R/S-6, and R/S-9, the amplified CPL signals (|gPL|) were detected as high as 2.36 × 10-2, 2.06 × 10-2, and 1.26 × 10-2 from blends of F8BT and these chiral inducers. The circularly polarized organic light-emitting diode (CP-OLED) device on the blends of F8BT and chiral inducers (R/S-6) with small dihedron angle and excellent carrier mobility showed a low turn-on voltage (Von < 4.5 V), high brightness (> 10509.6 cd/m2), and maximum |gEL| value of 1.86 × 10-2 (F8BT + 5% R/S-6). This work can develop and provide a valuable reference for CP-OLED device design through chiral dopant induction.

Deep Blue Circularly Polarized Luminescence Response Behavior of an Achiral Pyrene-Based Emitter Regulated by Chiral Co-assembly Helical Nanofibers.

Supramolecular co-assembly provides a brand-new powerful strategy for regulating simple organic molecules into various hierarchical nano- and microstructures as smart functional materials. In particular, chiral supramolecular assemblies with strong fluorescent emission have received extensive attention for their application as circularly polarized luminescence (CPL) emitters. Herein, we synthesized three achiral pyrene derivatives, but only the chiral co-assembly (R/S-NMe2-Py-2) can exhibit the regular and orderly helical nanofiber via π-π stacking interaction between chiral N,N'-dimethyl-binaphthyldiamine enantiomers (R/S-NMe2) and the achiral pyrene derivative (Py-2). Interestingly, this kind of 2:1 molar ratio (R/S-NMe2)2-Py-2 co-assembly with a helical nanofiber structure can emit a strong deep blue CPL signal from the achiral pyrene-based emitter, and the dissymmetry factor gem value can reach 0.027 (λem = 423 nm) in the film from spin-coating.

Interface Engineering of Anchored Ultrathin TiO2/MoS2 Heterolayers for Highly-Efficient Electrochemical Hydrogen Production.

An efficient self-standing hydrogen evolution electrode was prepared by in situ growth of stacked ultrathin TiO2/MoS2 heterolayers on carbon paper (CP@TiO2@MoS2). Owing to the high overall conductivity, large electrochemical surface area and abundant active sites, this novel electrode exhibits an excellent performance for hydrogen evolution reaction (HER). Remarkably, the composite electrode shows a low Tafel slope of 41.7 mV/dec, and an ultrahigh cathodic current density of 550 mA/cm2 at a very low overpotential of 0.25 V. This work presents a new universal strategy for the construction of effective, durable, scalable, and inexpensive electrodes that can be extended to other electrocatalytic systems.

Microchannel contacting of crystalline silicon solar cells.

There is tremendous interest in reducing losses caused by the metal contacts in silicon photovoltaics, particularly the optical and resistive losses of the front metal grid. One commonly sought-after goal is the creation of high aspect-ratio metal fingers which provide an optically narrow and low resistance pathway to the external circuit. Currently, the most widely used metal contact deposition techniques are limited to widths and aspect-ratios of ~40 µm and ~0.5, respectively. In this study, we introduce the use of a micropatterned polydimethylsiloxane encapsulation layer to form narrow (~20 µm) microchannels, with aspect-ratios up to 8, on the surface of solar cells. We demonstrate that low temperature metal pastes, electroless plating and atomic layer deposition can all be used within the microchannels. Further, we fabricate proof-of-concept structures including simple planar silicon heterojunction and homojunction solar cells. While preliminary in both design and efficiency, these results demonstrate the potential of this approach and its compatibility with current solar cell architectures.

Solution synthesis and phase control of inorganic perovskites for high-performance optoelectronic devices.

An efficient method to synthesize well-crystallized inorganic cesium lead halide perovskites (CsPbX3, X = I or Br) with high yield and high reproducibility was proposed. Notably, the as-prepared CsPbI3 in the yellow orthorhombic phase (y-CsPbI3) can be easily converted to the black cubic perovskite phase CsPbI3 (b-CsPbI3) after thermal annealing. Furthermore, two-terminal photodetectors and all-inorganic perovskite solar cells based on b-CsPbI3 were fabricated, exhibiting high performances.