Topoarchitected polymer networks expand the space of material properties.

Many living tissues achieve functions through architected constituents with strong adhesion. An Achilles tendon, for example, transmits force, elastically and repeatedly, from a muscle to a bone through staggered alignment of stiff collagen fibrils in a soft proteoglycan matrix. The collagen fibrils align orderly and adhere to the proteoglycan strongly. However, synthesizing architected materials with strong adhesion has been challenging. Here we fabricate architected polymer networks by sequential polymerization and photolithography, and attain adherent interface by topological entanglement. We fabricate tendon-inspired hydrogels by embedding hard blocks in topological entanglement with a soft matrix. The staggered architecture and strong adhesion enable high elastic limit strain and high toughness simultaneously. This combination of attributes is commonly desired in applications, but rarely achieved in synthetic materials. We further demonstrate architected polymer networks of various geometric patterns and material combinations to show the potential for expanding the space of material properties.

Bandgap tunable Csx(CH3NH3)1-xPbI3 perovskite nanowires by aqueous solution synthesis for optoelectronic devices.

To date, all the lead halide based full-inorganic or organic-inorganic hybrid perovskites have been synthesized from organic solvent, such as N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO), by a solution method. Herein, water has been utilized as a 'green' solvent to develop an efficient synthetic route to grow various kinds of lead halide perovskite nanowires (NWs). By controlling the proportion of the hybrid cations, Csx(CH3NH3)1-xPbI3 perovskite NWs were successfully synthesized. Every Csx(CH3NH3)1-xPbI3 perovskite NW demonstrated single crystal characteristics with uniform stoichiometric element distribution. Because of the controllable cation composition, the NW bandgaps could be finely tuned from 1.5 to 1.7 eV. Transient photoluminescence spectra showed superior NW quality when compared with those of the conventional DMF-based NWs. Based on the abovementioned high quality single Cs0.5(CH3NH3)0.5PbI3 perovskite NW, a reliable single-NW photodetector was fabricated to investigate the optoelectronic application. It demonstrated a responsivity of 23 A/W, exceeding most of the reported values in the perovskite nanowire photoconductive detectors, and the shot-noise normalized detectivity was 2.5 × 1011 Jones comparable to the parameters of the commercial silicon-based nanowires. The green and robust synthesis method, finely tunable NW bandgaps, and superior optoelectronic properties are expected to open a new door for the development of perovskite optoelectronic devices.

Low-Dimensional Halide Perovskites and Their Advanced Optoelectronic Applications.

Metal halide perovskites are crystalline materials originally developed out of scientific curiosity. They have shown great potential as active materials in optoelectronic applications. In the last 6 years, their certified photovoltaic efficiencies have reached 22.1%. Compared to bulk halide perovskites, low-dimensional ones exhibited novel physical properties. The photoluminescence quantum yields of perovskite quantum dots are close to 100%. The external quantum efficiencies and current efficiencies of perovskite quantum dot light-emitting diodes have reached 8% and 43 cd A-1, respectively, and their nanowire lasers show ultralow-threshold room-temperature lasing with emission tunability and ease of synthesis. Perovskite nanowire photodetectors reached a responsivity of 10 A W-1 and a specific normalized detectivity of the order of 1012 Jones. Different from most reported reviews focusing on photovoltaic applications, we summarize the rapid progress in the study of low-dimensional perovskite materials, as well as their promising applications in optoelectronic devices. In particular, we review the wide tunability of fabrication methods and the state-of-the-art research outputs of low-dimensional perovskite optoelectronic devices. Finally, the anticipated challenges and potential for this exciting research are proposed.

Improving the Performance of PbS Quantum Dot Solar Cells by Optimizing ZnO Window Layer.

Comparing with hot researches in absorber layer, window layer has attracted less attention in PbS quantum dot solar cells (QD SCs). Actually, the window layer plays a key role in exciton separation, charge drifting, and so on. Herein, ZnO window layer was systematically investigated for its roles in QD SCs performance. The physical mechanism of improved performance was also explored. It was found that the optimized ZnO films with appropriate thickness and doping concentration can balance the optical and electrical properties, and its energy band align well with the absorber layer for efficient charge extraction. Further characterizations demonstrated that the window layer optimization can help to reduce the surface defects, improve the heterojunction quality, as well as extend the depletion width. Compared with the control devices, the optimized devices have obtained an efficiency of 6.7% with an enhanced V oc of 18%, J sc of 21%, FF of 10%, and power conversion efficiency of 58%. The present work suggests a useful strategy to improve the device performance by optimizing the window layer besides the absorber layer.

Spectra-selective PbS quantum dot infrared photodetectors.

Traditional photoconductive photodetectors (PDs) commonly respond to higher energy photons compared with the bandgaps of PD active materials. Different from the wide detection spectra of traditional PDs, the present reported PbS quantum dot (QD) PDs can detect the spectra-selective light source. Spectra-selective PDs (ss-PDs) of perovskite/QDs and QD/QDs were respectively implemented by integrating two functional layers. The top layer (facing the light) was utilized to filter the non-target spectra and the bottom layer was used for detection. The response spectrum wavelength and the range of ss-PDs can be conveniently tailored by tuning the QD size. The obtained selectivity factor and normalized detectivity ratio from target and non-target illumination can reach at least 10. A narrow detection range with a full width at half maximum (FWHM) ∼100 nm was applied by typical QD/QD based ss-PDs. The prototype ss-PDs were successfully applied in identifying an unknown light source. The convenient tuning and identification capabilities of the present QD based ss-PDs may provide a versatile route to obtain highly spectrum-selective PDs in order to meet the demands for special fields.

Flexible and Semitransparent Organolead Triiodide Perovskite Network Photodetector Arrays with High Stability.

Organolead triiodide perovskite (CH3NH3PbI3) as a light-sensitive material has attracted extensive attention in optoelectronics. The reported perovskite photodetectors (PDs) mainly focus on the individual, which limits their spatial imaging applications. Uniform perovskite networks combining transparency and device performance were synthesized on poly(ethylene terephthalate) (PET) by controlling perovskite crystallization. Photodetector arrays based on above network were fabricated to demonstrate the potential for image mapping. The trade-off between the PD performance and transparency was systematically investigated and the optimal device was obtained from 30 wt % precursor concentration. The switching ratio, normalized detectivity, and equivalent dark current derived shot noise as the critical parameters of PD arrays reached 300, 1.02 × 10(12) Jones, and 4.73 × 10(-15)A Hz(-1/2), respectively. Furthermore, the PD arrays could clearly detect spatial light intensity distribution, thus demonstrating its preliminary imaging function. The perovskite network PD arrays fabricated on PET substrates could also conduct superior flexibility under wide angle and large number of bending. For the common problem of perovskite optoelectronics in stability, the perovskite networks sheathed with hydrophobic polymers greatly enhanced the device stability due to the improved interface contacts, surface passivation, and moisture isolation. Taking into consideration transparency, flexibility, imaging and stability, the present PD arrays were expected to be widely applied in visualized portable optoelectronic system.

Growth, patterning and alignment of organolead iodide perovskite nanowires for optoelectronic devices.

Organolead halide perovskites are becoming intriguing materials applied in optoelectronics. In the present work, organolead iodide perovskite (OIP) nanowires (NWs) have been fabricated by a one step self-assembly method. The controllable NW distributions were implemented by a series of facile techniques: monolayer and small diameter NWs were prepared by precursor concentration tuning; NW patterning was achieved via selected area treatment assisted by a mask; NW alignment was implemented by modified evaporation-induced self-assembly (EISA). The synthesized multifunctional NWs were further applied in photodetectors (PDs) and solar cells as application demos. The PD performances have reached 1.32 AW(-1) for responsivity, 2.5 × 10(12) Jones for detectivity and 0.3 ms for response speed, superior to OIP films and other typical inorganic NW based PD performances. An energy conversion efficiency of ∼2.5% has been obtained for NW film based solar cells. The facile fabrication process, controllable distribution and optoelectronic applications make the OIP NWs promising building blocks for future optoelectronics, especially for low dimensional devices.

Plasmon-enhanced fluorescence of PbS quantum dots for remote near-infrared imaging.

Gold nanoparticles with nanoscale protrusions can be synthesized by seed-mediated growth in favor of tuning the surface plasmon band towards the near-infrared regime. Electromagnetic field enhancement makes significant contribution to improve fluorescence emission of PbS quantum dots in the near-infrared window, identifying their application in remote imaging by collecting the scattered fluorescence of their hybrids.