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Magnetic resonance imaging (MRI) is one of the most popular techniques in brain science and is important for understanding brain function and neuropsychiatric disorders. However, the processing and analysis of MRI is not a trivial task with lots of challenges. Recently, deep learning has shown superior performance over traditional machine learning approaches in image analysis. In this survey, we give a brief review of the recent popular deep learning approaches and their applications in brain MRI analysis. Furthermore, popular brain MRI databases and deep learning tools are also introduced. The strength and weaknesses of different approaches are addressed, and challenges as well as future directions are also discussed.

Purified desulphated glucosinolates (GSLs) were subjected to thermal treatment in model systems without interference to investigate the formation of volatile components derived from GSLs only. Desulphated progoitrin (PRO), desulphated gluconapin (GNA), and desulphated glucobrassicanapin (GBN) were isolated from rapeseed (

Hole-transport material-free (HTM-free) perovskite solar cells (PSCs) have the advantages of low manufacturing cost and excellent stability, however, the power conversion efficiencies (PCEs) of these PSCs are relatively low due to the high recombination rate at charge transport interface contacts. Herein, a novel bilayer electron-transport scaffold of SiO2/NaYF4:Yb,Er@SiO2 modified TiO2 nanorods was designed to improve the performance of HTM-free PSCs. Facilitated by the 1D nanorods structure of underneath TiO2 scaffold, photogenerated charges can be quickly transported out of perovskite film with reduced recombination, and the NaYF4:Yb,Er@SiO2 insulating capping layer can further inhibit the charge recombination by removing charge shorting pathways caused by the tangle of TiO2 nanorods with carbon back contact. Moreover, NaYF4:Yb,Er can upconvert near-infrared light into visible region that can be directly used by perovskite materials to improve the current density of corresponding PSCs. Our PSCs have an average PCE of 14.01 ± 0.53%. We demonstrated that up-conversion of light at 980 nm was possible but up-conversion made no statistical improvement in performance.

Organic single crystals have great potential in optoelectronic devices owing to their grain-boundary free nature and long exciton diffusion length. In this report, an anthracene linked benzo[b]benzo[4,5]thieno[2,3-d]thiophene semiconductor, 2-An-BTBT was designed and synthesized. Belt like organic single crystals based on 2-An-BTBT were grown via physical vapor transport method. Using an ultrathin wire as the shadow mask, organic field effect transistor (OFET) with a channel length of around 15 μm was fabricated and the highest mobility of 0.9 cm2V−1s−1 and average mobility of 0.58 cm2/V were obtained. Furthermore, photo-response characteristics of the 2-An-BTBT based device were also investigated. Photo-response of as high as 7136 AW-1 was achieved via 17.7 μW/cm2 @380 nm mono wavelength light illumination which is ascribed to the long exciton diffusion length of organic single crystal and ultra-short channel length of the fabricated OFET. Stable switching behavior with rising time and decline time of several seconds is attained which indicates the existence of shallow traps at the insulator/semiconductor interface.

As the scaling of silicon-based field-effect transistors has approached its physical limits, the search for alternative channel materials for future logic devices has attracted much attention. The discovery of graphene has unveiled another material family with layered structures called two-dimensional (2D) materials. Black phosphorus (BP), the most stable allotrope of phosphorus, was introduced as a new type of 2D material in 2014. Thanks to its high mobility, in-plane anisotropy and direct band gap, BP is considered to be a promising candidate for next-generation electronic and optoelectronic devices. Numerous studies have demonstrated the beneficial effects of introducing BP for device architectures. Herein, we present a review outlining recent progress towards high performance BP-based transistors. This review starts with the fundamental properties of BP, including its crystal structure, bandgap, and direct current (DC) and radio-frequency (RF) characteristics, followed by a detailed description of the modulation and application of those properties, involving anisotropy, functionalization and superlattices. Furthermore, we also discuss device design for high-performance transistors, with particular emphasis on interface engineering and device stability. Finally, we offer our perspective on the future of BP electronics, aiming to benefit colleagues who are interested in this exciting research field.

The electrochemical performance of lithium ion batteries depend largely on the structural properties of electrode materials. In this work, we propose an approach to synthesize lithium-rich layered oxides (LLOs) materials using a manganese dioxide (MnO2) template strategy, which could control the structure and particle size of final products via choosing different MnO2 templates. Through precisely optimizing, we successfully prepare cross-linked nanorods (CLNs) and agglomerate microrods (AMs) Li1.2Ni0.15Co0.1Mn0.55O2 cathode materials by using carbon-decorated MnO2 nanowires and MnO2 nanorods as templates, respectively. The lithium ion battery based on the CLNs exhibits excellent performance, delivering a high capacity of 286.2 mAh g−1 at 0.1 C and 237.5 mAh g−1 at 1 C. In addition, the device remains 98% and 89% of its initial capacity after 50 cycles at 0.1 C and 100 cycles at 1 C, respectively. The remarkable electrochemical performance can be mainly attributed to the cross-linked nanorods structure which can provide relatively shorter lithium ion diffusion length, larger reaction surface and more internal cavity. This universal structure engineering strategy may shed light on new material structures for high performance lithium-rich layered oxide cathode materials.

Surface passivation of the electron transport layer in perovskite solar cells has been proven to be one crucial strategy to improve the power conversion efficiency. In this study, we introduce rutile phase titania shell to passivate anatase TiO2 scaffold, forming anatase@rutile mixed-phase TiO2 scaffold in hole-conductor-free carbon based perovskite solar cells. Anatase@rutile mixed phase TiO2 films exhibit higher conductivity, faster charge extraction, lower trap density and suppressed charge recombination at the interface of TiO2/perovskite films in the modified devices as well, achieving a champion power conversion efficiency of 15.21% for carbon based perovskite solar cells. More importantly, benefiting from the stable and better ultraviolet light filtration properties of rutile phase TiO2, our devices exhibit excellent stability maintaining 92% of their initial efficiency after 200 days storage in ambient air, highlighting their merits as a potential competitor for future industrial photovoltaics.

The preparation of high-quality perovskite films with low defect density and long carrier lifetime is a precondition for achieving high-efficiency perovskite solar cells (PSCs). In this work, we successfully incorporated Y3+ ions into perovskite films to enhance the photovoltaic performance of hole-transport-layer-free (HTL-free) carbon-based MAPbBr3 PSCs in ambient atmosphere. The perovskite films exhibit better crystallinity, lower trap density, and longer carrier lifetime after the introduction of Y3+ ions. By optimizing the doping dosage, a maximal power conversion efficiency (PCE) of 8.313% (open-circuit voltage (VOC) = 1.562 V) is achieved for MAPb0.98Y0.02Br3 PSCs. Moreover, the unencapsulated device also shows remarkable long-term stability over 80 days under dry condition with 20–30% relative humidity (RH) at 20–25 °C, which even maintains 95% of its initial PCE when stored in harsh environment (80 °C and 40–70% RH) over 72 h.

Controllable three-dimensional villose titanium dioxide architectures grown on carbon textiles are fabricated by a facile one-step in-situ hydrothermal method at low temperatures. It has in fact been proven to be an effective method to reduce self-aggregation and promote lithium-ion intercalate/extract via building 3D architectures based on 2D conductive materials. More importantly, the freestanding electrodes without any addition of conductive agents and polymeric binders reveal significant improvement in high-rate capacity and cycling performance.

Herein, we demonstrate a sustainable strategy for scalable production of α-Fe2O3 nanocrystals on flexible carbon textiles via controllable chemical bath deposition process. The assembly of α-Fe2O3 nanocrystals is densely anchored onto the carbon textiles, and the temperature-dependent mass loading and crystal size of α-Fe2O3 are systematically investigated. As an integrated electrode for lithium-ion batteries, the optimized Fe2O3@CTs with ultrathin three-dimensional interconnected porous architectures achieves significantly enhanced cycling performance and rate capability attributing to the improved stability, electronic interconnection, and shortened solid state diffusion pathway for Li+ ions/electrons. After the reactivation of the precursor, the Li-ion batteries based on the recycled Fe2O3@CTs exhibits electrochemical performance with no decay compared to that of the devices based on the fresh products. This sustainable methodology, considering material abundance, eco-efficiency, synthetic approach and scalability, is of crucial importance to both academy and industry for achieving high-performance lithium-ion batteries.

Perovskite nanocrystals (PNCs) have emerged as advanced materials for various applications. Herein, we developed oxygen insensitive PNCs in polymer matrices and applied them as internal reference to achieve ratiometric sensing for oxygen. Significant emission color changes from orange under nitrogen to green under oxygen were observed. Further micro-patterned sensors were prepared by micro/nano-imprint technology. Results showed that all these micro-structures increased sensors’ sensitivity, however, affected sensors response time significantly. The film with pinholes slowed down the response times; the films with pillars shorted the response time. Therefore, for the first time we prepared new PNCs-based ratiometric gaseous oxygen sensing films and further prepared micro-structured sensors. This study may broaden the applications of perovskite materials and also oxygen sensors.

Cell encapsulation based on droplet microfluidics has been widely adopted in single cell researches, and corresponding highly-uniform cell-laden microgels play significant roles in tissue engineering and cell therapy. However, the encapsulation always faces challenges to maintain favorable cell viability. Herein, based on a double flow-focusing regime, cells were encapsulated in biocompatible sodium alginate droplets, and enveloped in oil droplets to form double emulsions. Ca2+ ions in the outer aqueous phase diffused through the oil and introduced the gelation of sodium alginate to form cell encapsulation. This indirect gelation process and the spontaneous detachment of oil helped to keep cell viability well, which was validated by FDA/PI staining tests.

Sodium tetrahydroborate (NaBH4) and dodecahydro-closo-dodecaborate (Na2B12H12) are both important inorganic compounds presenting multiple applications. Nevertheless, multistep and complicated conditions are usually demanded for their synthesis. In order to simplify the synthesis processes, we design a novel and facile solvent-free method for synthesizing NaBH4 or Na2B12H12 from NaNH2 and B10H14. The product of either NaBH4 or Na2B12H12 is manipulable by simply adjusting the ratio of NaNH2 to B10H14. The reaction equations of synthesizing NaBH4 and Na2B12H12 are proposed and verified, and the reaction pathways are elucidated. The findings here supply new insight to synthesize metal dodecaborates using the strategy of equal electron body for the first time and may shed light on synthesis of small metal B-H compounds from large B-H clusters.

Metallic Li, with ultrahigh theoretical capacity (3860 mA h g−1) and the lowest electrochemical potential (−3.04 V vs. the standard hydrogen electrode), is perfectly meet the needs of high energy density lithium batteries. However, the direct use of metallic lithium as anode would cause serious dendrite and huge volume expansion, which will bring safety hazards and restrict the practical commercialization of Li metal anodes. Herein, a facile electrophoretic deposition (EPD) method was employed for the first time to fabricate uniform TiN modified commercial Cu foam (TiN@Cu foam) as the lithiophilic 3D conductive skeleton. The lithiophilic TiN acts as the well-distributed seeds to promote the uniform lithium deposition, attributing to the lowed nucleation overpotential. The porous and conductive Cu foams can further mitigate the formation of Li dendrites, on account of its high specific surface area reduce the effective current density. The TiN@Cu foam based half cells and symmetric cells both exhibit improved reversibility and reduced polarization voltage in lithium plating/stripping process. Furthermore, better rate performance and cycling stability were also achieved in the full-cell configurations of TiN@Cu foam-Li/Li4Ti5O12 (LTO) and TiN@Cu foam-Li/LiFePO4 (LFP). This work demonstrates a facile strategy to modify the commercial current collectors with pre-synthesized lithiophilic nanoparticles for achieving uniform Li deposition.

The TiO 2 nanotubes (TNT) are synthesized and decorated with Au nanoparticles, forming a TNT-Au composite. This TNT-Au composite is incorporated into a TiO 2 nanocrystalline film to form a multifunctional composite photoanode and the dye-sensitized solar cell (DSSC). The influences of different amounts of TNT-Au on the performance of the multifunctional composite photoanodes and DSSCs are investigated. Studies indicate that, the introduction of TNT-Au improves remarkably the transport rate of electrons, enhances the ability of photoanode to scatter and capture incident light, reduces the charge transfer resistance, and thereby improves significantly the short-circuit current density (J sc ) and photoelectric conversion efficiency (PCE) of the DSSCs. The maximal J sc of 14.72 mA cm −2 and PCE of 6.94% are obtained in the optimal DSSC with 10 wt% TNT-Au, significantly higher than those of the DSSC with pure TiO 2 photoanode by 24.3% and 21.8%, respectively. These remarkable improvement in the properties of the DSSCs can be attributed to the strong scattering of TNT for incident light, fast charge transfer of TNT due to their unique one dimensional hollow structure, and the surface plasmon resonance of Au nanoparticles, in a tri-synergistic and complementary fashion.

It is a great challenge to prepare high quality perovskite films in ambient atmosphere with high humidity (≥ 50%), since the commonly adopted two step sequential deposition process produces perovskite films with rough surfaces and a large amount of residual PbI 2 . To solve these problems, a facile method using combined solvent and vapor treatment is proposed. The residual PbI 2 is diminished through a solvent treatment process, and then smooth perovskite surface with micrometer scaled perovskite particles is obtained with a CH 3 NH 2 vapor treatment. The quality of the obtained perovskite films is examined in the hole transport material free perovskite solar cells, and power conversion efficiency is boosted up by 17.3% compared with the traditional method. When a CuPc hole transport layer is further introduced, carbon counter electrode based perovskite solar cells exhibit a superior power conversion efficiency of 16.61%. Thus this method shows great potential in further optimizing the performance of perovskite solar cells.

We report on compositional and morphological engineering of mixed methylammonium (MA) and formamidinium (FA) lead triiodide (MA1−xFAxPbI3) perovskite absorber layers to produce highly efficient planar and flexible perovskite solar cells (PVSCs) with reduced hysteresis. Incorporation of FA into the MAPbI3 extends the absorption edge of the perovskite to longer wavelengths, leading to enhanced photocurrent of the resultant PVSCs. Moreover, adding a small amount of lead thiocyanate (Pb(SCN)2) additive into mixed perovskite precursor solutions significantly enlarges the grain size and prolongs the carrier lifetime, leading to improved device performance. With optimal compositional and morphological engineering, the average power conversion efficiency (PCE) improves from 15.74±0.74% for pure MAPbI3 PVSCs to 19.40±0.32% for MA0.7FA0.3PbI3 PVSCs with 3% Pb(SCN)2 additive, exhibiting a high reproducibility and small hysteretic behavior. The best PVSC achieves a PCE of 20.10 (19.85)% measured under reverse (forward) voltage scan. Furthermore, the compositional and morphological engineering allowed the fabrication of efficient flexible PVSCs on indium-doped SnO2 (ITO)/polyethylene terephthalate (PET) substrates, with the best PCE of 17.96 (16.10)% with a VOC of 1.076 (1.020) V, a JSC of 22.23 (22.23) mA/cm2 and a FF of 75.10 (71.02)% when measured under reverse (forward) voltage scan. Our approach provides an effective pathway to fabricate highly efficient and reproducible planar PVSCs.

Due to its unique advantages such as monodispersity and high throughput, droplet microfluidics has been widely used to generate diverse droplets/particles that have specific structures. Herein, we implemented Janus droplet parallel arrangements in a flow-focusing microchip through regulating corresponding fluid flow rates. Initially, fluorescence dye and PBS buffer solution kept laminar flow before the flow-focusing orifice and then was sheared into Janus droplets. Droplet diameter and corresponding generation frequency could be effectively manipulated. Subsequently, the generation of different Janus droplet parallel arrangements (e.g. monolayer, double-layer or three-layer arrangement) could be achieved by fluid regulation.

Doping of TiO2 by metal elements for the scaffold layer of the perovskite solar cells has been proved to be one of the effective methods to improve the power conversion efficiency. In the present work, we report the impact of doping of TiO2 nanoparticles with different amounts of tungsten (W) on the photovoltaic properties of hole transport material free perovskite solar cells (PSCs) that employ carbon counter electrode. Light doping with W (less than 1000 ppm) improves the power conversion efficiencies (PCEs) of solar cells by promoting the electron conductivity in the TiO2 layer which facilitates electron transfer and collection. With the incorporation of W, average efficiency of PSCs is increased from 9.1% for the un-doped samples to 10.53% for the 1000 ppm W-doped samples, mainly originates from the increase of short circuit current density and fill factor. Our champion cell exhibits an impressive PCE of 12.06% when using the 1000 ppm W-doped TiO2 films.

Circulating tumor cells (CTCs) have been believed to hold significant insights for cancer diagnosis and therapy. Here, we developed a simple and effective method to capture and release viable CTCs using core-shell Fe 3 O 4 @MnO 2 nanoparticles. Fe 3 O 4 @MnO 2 nanoparticles bioconjugated with anti-EpCAM antibody have characteristics of specific recognition, magnetic-driven cell isolation and oxalic acid-assisted cell release. The capture and release efficiency of target cancer cells were ∼83% and ∼55%, respectively. And ∼70% of released cells kept good viability, which could facilitate the subsequent cellular analysis.

Single-phase and Dy 3+ /Eu 3+ co-doped novel phosphor LiY(MoO 4 ) 2−x (WO 4 ) x :Dy 3+ ,Eu 3+ , emitting white luminescence under near ultraviolet (NUV) light, was prepared through sol-gel method. The preparation and characterization of this phosphor were systematically studied by X-ray diffraction and spectrofluorophotometric measurements. The molar ratio of metal ions and citric acid (R m/c ) and calcination temperature greatly influenced the phase purity of sample, revealing that the pure phase could be obtained by using R m/c = 1:2.5 and calcination temperature = 800 °C. Under NUV excitation, the as-prepared phosphor exhibited the emissions of 485, 572 and 612 nm, which intensities could be affected by the pH and the concentrations of molybdenum and tungsten ions. By doping appropriate concentrations of Dy 3+ and Eu 3+ , white light emitting phosphor LiY(MoO 4 ) 1.2 (WO 4 ) 0.8 :6%Dy 3+ ,7%Eu 3+ with good responsiveness to NUV light was obtained. The Commission Internationale de L’Eclairage chromaticity coordinates were calculated to be (x = 0.334, y = 0.322), close to the D 65 illuminant (x = 0.313, y = 0.329), indicating the potential application for NUV WLEDs.

Flexible semitransparent perovskite solar cells (PVSCs) hold promising applications on buildings and unmanned vehicles with irregular surfaces. Efficient wide-bandgap PVSCs are a determining factor for building perovskite-based tandem cells, in which energy level alignment plays significant roles in reducing nonradiative recombination loss at interfaces. Here, we report on the fabrication of efficient flexible semitransparent wide-bandgap PVSCs with gradient energy level alignments at both electron- and hole-selective contacts. We design a triple-electron-selective contact as electron transport layers with gradient Fermi level alignment with the conduction band of wide-bandgap perovskite, which consists of trans-1,2-Diaminocyclohexane-N,N,N′,N′-tetraacetic (CyDTA), tin dioxide (SnO2), and CyDTA-complexed SnO2. Moreover, an ultrathin gold layer embedded between 2,2′,7,7′-tetrakis(N,N-bis(p-methoxy-phenyl)amino)-9,9′-spirobifluorene (spiro-OMeTAD) hole transport layer and molybdenum oxide protection layer facilitates effective hole transport to the anode. We conduct comprehensive and solid simulation at both charge-selective contacts to reveal the working mechanisms. The champion flexible semitransparent 1.75 eV wide-bandgap PVSC achieves an efficiency of 15.02% with excellent light transparency of around 70% beyond the wavelength of 700 nm, enabling all-flexible perovskite/Cu(In,Ga)Se2 tandem devices with efficiencies beyond 21%.

A facile approach to fabricate low-cost hole-transport-material (HTM)-free perovskite solar cell(PSC) based on commercial P25 nanoparticles and bilayer hybrid carbon electrode under ambient condition is reported. The performance of such HTM-free PSCs are highly dependent on the thickness and morphology of the P25 based TiO 2 electron-transport layer(ETL), which can be adjusted by the amount of ethanol and ethyl cellulose in the paste. After optimization, a power conversion efficiency of 12.48% is obtained, which is enhanced by 20.46% compared with solar cells employing hydrothermal TiO 2 ETL. In addition, PSCs with P25 ETL also exhibit excellent long-term stability together with reduced hysteresis. With advantages of low-cost, high efficiency and facile fabrication process, commercial P25 nanoparticles based PSC is highly potential for future commercialization.

Dye-sensitized solar cells (DSCs) have attracted widespread attention in recent years, attributed to their low production costs, facile fabrication and tunable optical properties. In order to achieve competitive conversion efficiencies, the sunlight harvesting capacities of DSCs should be improved over a broad range of wavelengths and incidence angle. Here, we demonstrate a facile strategy to enhance the light absorptions of the devices via employing self-organized cholesteric liquid crystal (CLC) polymer films as transparent and flexible back-reflectors for DSCs. The photonic band gap of these CLC films can be precisely tailored by modulating the helical pitch and twist sense. The selective light reflection of these CLC films gives rise to the possibility for increasing the optical path length of the light in particular wavelength region while retaining the cell transparency. The enhancement of photocurrent and power conversion efficiency (PCE) reveals strong wavelength dependence owing to the selective reflection of these CLC polymer films. The DSCs with proper combination of CLC back-reflectors yield the maximum enhancement over 21% in photocurrent and 17% in PCE. The work presented here provides new insights into the design of cell geometry for achieving extra absorption enhancement, which can also be compatible with other photovoltaic concepts.

The morphology of PbI 2 film plays a critical role in determining the quality of the resultant CH 3 NH 3 PbI 3 film and power conversion efficiency of CH 3 NH 3 PbI 3 perovskite solar cell. Here, we propose a solvent treatment method in the two-step sequential deposition process to control the morphology of PbI 2 film, which leads to enhanced power conversion efficiency. Hole transport material free perovskite solar cell is chosen as a paradigm to demonstrate this idea. Solvent (isopropanol, chlorobenzene, or ethanol) treated PbI 2 films exhibit dendrite-like or flake-like morphologies, which facilitate more complete conversion of PbI 2 to CH 3 NH 3 PbI 3 perovskite in ambient atmosphere with a relative high humidity. Therefore, enhanced performance is obtained with the solvent treated PbI 2 films. Average power conversion efficiency has been improved from 9.42% in the traditional two-step sequential deposition to 11.22% in solar cells derived from ethanol treated PbI 2 films.

Both upconversion of near-infrared light and surface plasmon resonance (SPR) of nobel metal nanoparticles (NPs) show potential application in dye-sensitized solar cells(DSSCs). For the first time, the novel multi-shell-coated and Au-NPs decorated hexagonal submicron β-NaYF4:Yb3+, Er3+(NFYE)@SiO2@Au@TiO2(NSAT) prisms were prepared and incorporated into the photoanodes of DSSCs. The influences of different coating layers and decorated Au-NPs on the upconversion of NFYE and the performance of DSSCs were comparatively investigated. Studies indicated that the coated multi-shells have great influences on the upconversion and the properties of DSSCs. The Au-NPs can remarkably enhance the intensity of upconversion luminous emission and thus the short-circuit current density (Jsc) and photoelectron conversion efficiency (η) of the DSSCs. The TiO2 shell is beneficial for absorbing more dye and lowering the interface transport resistance. The optimal Jsc and η obtained in a typical DSSC containing NSAT are 18.62 mA/cm2 and 7.79%, respectively, corresponding 38.2% and 28.1% higher than that of the DSSC with a pure TiO2 photoanode. This significant improvement can be mainly attributed to the enhanced upconversion emission of the NSAT prisms arising from the SPR effect of the embeded Au-NPs and to the possible enhanced scattering from the submicron prisms.

Hierarchical TiO 2 spheres (HTS) containing needle–like nanorods and decorated with Au nanoparticles are synthesized, forming the HTS-Au microspheres. These microspheres are hybridized into TiO 2 nanocrystalline film to act as a scattering body on top of a pure TiO 2 nanocrystalline layer, forming a novel composite photoanode. The effects of such HTS-Au microspheres on the performance of the photoanode and dye-sensitized solar cell (DSSC) are studied. Study reveals that both light absorption and scattering in the photoanode are greatly enhanced, leading to the significant increases of the short-circuit current density (J sc ) and photoelectric conversion efficiency (η) of the DSSC. The optimal HTS-Au-based DSSC exhibits the maximum J sc of 14.56 ± 0.20 mA cm −2 and η of 7.37 ± 0.05%, markedly higher than those of the pure TiO 2 -NPs-based DSSC by 23.4% and 23.0%, respectively. The great improvements in the properties of the optimal HTS-Au-based DSSC can be mainly attributed to these factors: the heightened light absorption owing to the localized surface plasmon resonance from Au nanoparticles, the higher light scattering ability by the HTS microspheres, and the possible faster electron transfer channel provided by the needle-like nanorods. These different functions play important complementary roles in enhancing the light harvesting, the J sc and η of the DSSC.

A facile method is developed to prepare NiCo2S4 counter electrode (CE) which is in-situ grown on SnO2: F transparent conductive glass (FTO) with mirror-like smooth surface. As demonstrated by analyses, the electrocatalytic activity, electrical conductivity and light reflectivity of the NiCo2S4 CE exceed or approach to those of Pt-sputtering CE, and are much better than those of Pt-pyrolysis CE. Thus the conversion efficiency (η) of the dye sensitized solar cell (DSSC, 8.10%) based on NiCo2S4 CE is higher than the cell based on Pt-sputtering CE (7.60%), and is superior to the one based on Pt-pyrolysis CE (7.01%). Remarkably, NiCo2S4 CE also exhibits excellent chemical and mechanical stability. There are almost no changes on morphology and interfacial adhesion between NiCo2S4 film and FTO substrate after sequential 1000-time scans of cyclic voltammetry and 100 cycles of 3 M Scotch tape detachment. The η of DSSC drops a little from 8.10% to 7.94%. The numerous superiorities of the Pt-sputtering-like NiCo2S4 CE permit its promising application in DSSCs.

We have designed a novel hole-conductor-free and insulation layer free mesoscopic perovskite solar cells (PSCs) with a low cost carbon counter electrode (CE). Significantly, to enhance solar light harvesting capability, a mixture of methylammonium (CH3NH3+, MA) and formamidinium (HNCHNH3+, FA) cations were explored to synthesize superior performance perovskite materials. With the introduction of FAI, Cubic: Column composite structure of (FA)x(MA)1-xPbI3 was formed on the top of mesoscopic TiO2. This nanostructure not only leads to fully coverage of perovskite on TiO2 but also provides salutary electron transport channels to effectively reduce the electron recombination probability. As a result, optimal solar cell efficiency of 13.03% of (FA)x(MA)1-xPbI3 composite structure based PSC (when x is fixed at 0.25) was achieved, while PSC based typical MAPbI3 cuboids only obtained an efficiency of 12.49%. Despite of the improved efficiency, the Cubic: Column composite structure caused by the addition of FAI also contributes to higher long-term and thermal stability.

We demonstrate a facile approach to synthesize shape-controlled anatase titania with tailored facets via the employment of 3-aminopropyltrimethoxysilane (APTMS) as shape-tunable and capping agent. The as-synthesized anatase TiO2 nanorods was highly crystalline and exposed with {001} and {100} facets. The LIBs based on these highly crystalline TiO2 nanorods with tailored facets reveals significant improvement in high-rate capacity and cycling performance. More importantly, this methodology enable the industrial application of anatase titania as anode materials for LIBs without high temperature annealing process.

We synthesized highly uniform Au-decorated core-shell β -NaYF 4 :Er/Yb@SiO 2 microprisms and investigated its coupling effects on the performance of dye-sensitized solar cells (DSCs). The incorporation of upconversion phosphors (UCPs) and localized surface plasmon resonance (LSPR) arising from Au nanoparticles (AuNPs) was beneficial to achieve a higher photocurrent and power conversion efficiency of the devices. Furthermore, the contribution and interaction between upconversion and LSPR on the performance of DSCs were identified by UV–vis spectroscopy, upconversion fluorescence spectroscopy, and J - V characterization under different simulated illuminations. The presence of AuNPs increased the optical absorption of dye molecules in the visible region, but decreased the emission of UCPs. Thorough analysis showed that the energy of upconversion emission was transferred to the upconversion induced LSPR of AuNPs, that resulted from the incorporation between the SPR band of AuNPs and a matched emission bands of UCPs. These results validated the advantages of incorporation between upconversion and LSPR for DSC applications and revealed the underlying enhancement mechanism.

TiO 2 pyramids with planar-surface morphology presenting in the phases of anatase and brookite are successfully prepared, the height of which is 300-500 nm and 80-200 nm wide at the bottom. The pyramids exhibit excellent reflectance in the visible-near infrared region. When introducing the pyramids as a scattering layer covering the layer composed of TiO 2 nanoparticles, the energy conversion efficiency of dye-sensitized solar cell (DSSC) is enhanced from 6.49% to 7.25%. However, the pyramids overlayer falls from the nanoparticles underlayer easily, and the fill factor of the DSSC with the pyramids layer also become much lower. To solve the problem, we substitute TiO 2 microspheres underlayer for NP underlayer. As the tips of pyramids could be inserted into the submicron-sized gaps between the TiO 2 microspheres, the interface connection between layers of photoanode is reinforced. Current-Voltage measurement shows that the fill factor of the DSSC is much improved, and the DSSC has achieved 8.35% energy conversion efficiency. This study shows that the novel bilayer photoanode with improved light utilization and interface connection is an interesting structure for high efficiency DSSCs.

The β -NaYF 4 :Er 3+ /Yb 3+ hexagonal submicro-prisms coated with SiO 2 forming core–shell structures (NYFYE@SiO 2 ) and graphene oxide have been synthesized via a hydrothermal route. These NYFYE@SiO 2 prisms and graphene were both introduced into TiO 2 nanocrystalline films to form multi-functional-layers hybrid composite photoanodes and their dye-sensitized solar cells (DSSCs). The influence of various hybrid architectures of the composite photoanodes on the performances of the photoanodes and DSSCs were explored. Studies revealed that the graphene doping obviously increased the dye absorbed in the photoanode, the short-circuit current density (J sc ) and photoelectric conversion efficiency (η) of the DSSC. The adding of the NYFYE@SiO 2 prisms significantly increased the light scattering and near-infrared light harvesting of the photoelectrode, among which the SiO 2 coating layer on the prisms played an important role in reducing the photoelectron recombination and thus increasing the J sc of the DSSC. The J sc and η of the DSSC were significantly enhanced due to the complementary role between the UC of the NYFYE@SiO 2 and the graphene. The optimal properties with a J sc of 14.63 mA/cm 2 and η of 7.16% are obtained in the DSSC with the codoped composite photoanode, increasing significantly by 21.5% and 25.6%, respectively, in comparison with those of the DSSC with pure TiO 2 photoanode. Our studies demonstrated that codoping in photoanode with materials of complementary functions is an effective way to improve the performance of DSSCs.

A facile way of fabricating efficient blocking layer on mesoporous TiO2 film of dye-sensitized solar cells (DSSCs) is demonstrated here for the first time. Al2O3 and TiO2 are combined together to form a blocking layer. A simple spin coating technique is employed which is a versatile and low-cost method over the atomic layer deposition (ALD) technique. Multifunctional alumina/titania (Al2O3/TiO2) hybrid overlayer is prepared on traditional TiO2 nanocrystalline thin film surface, through sequential deposition of AlCl3·6H2O and TiCl4 precursor solutions followed by sintering at 500 °C for 30 min. Al2O3 effectively plays its role in retarding interfacial recombination of electrons and improving open circuit potential (Voc), while the tiny TiO2 clusters synthesized from TiCl4 treatment act as electron transporting channels to facilitate electron diffusion which leads to enhanced photocurrent (Jsc). Compared to the device without blocking layer, the DSSCs assembled with Al2O3/TiO2 hybrid blocking layer showed improvement in Jsc (from 13.09 mA/cm2 to 16.90 mA/cm2) as well as in Voc (from 0.72 V to 0.73 V) resulting a much better conversion efficiency of 8.60%.

Bifacial wafer-scale silicon nanowire arrays have been prepared through controllable deposition and metal-assisted chemical etching. Highly uniform silicon nanowire arrays with ultra-high aspect ratio have been obtained on both sides of the silicon wafer. The effects of Ag, HF, and H 2 O 2 on the formation mechanism have been systematically investigated. The results indicated that the influence of H 2 O 2 on the length of silicon nanowires, the surface density of arrays and the thickness of silicon wafer is more obvious than that of HF. Furthermore, the relationship between the length of silicon nanowires and the molar ratio of HF/H 2 O 2 has been investigated. It demonstrated that the length of silicon nanowires is proportional to ρ when the concentration of HF in the etchant is constant, but in inversely proportion to ρ when the concentration of H 2 O 2 is constant, where ρ is defined as [HF]/( [HF]+ [H 2 O 2 ]). This strategy will be beneficial and revelatory for fabrication of bifacial solar cells based on this wafer-scale silicon nanowire arrays.

A series of dye-sensitized solar cells (DSSCs) with differing amounts of Au nanorods (AuNRs) (coated with a SiO 2 layer as a core–shell AuNR@SiO 2 (AuNRS)) composited photoanodes are prepared. The influences of different amounts of AuNRSs on the performance of the composite photoanodes and DSSCs are investigated. Studies revealed that, by increasing the amount of AuNRSs, the intensity of the light absorption spectra of the photoanodes is gradually increased while the dye absorbed is reduced. The short-circuit current density ( J sc ), open-circuit voltage ( V oc ) and photoelectric conversion efficiency ( η ) increased gradually first and then decreased with the increase of AuNRSs, while the charge transfer resistance R 2 and the dark current showed an opposite change trend. The optimal properties were obtained in the 2.0 wt% AuNRSs doped DSSC, with a maximum J sc of 15.88 mA cm −2 , a highest V oc of 730 mV and a best η of 7.21%, giving 20.8%, 38 mV and 23.0% higher than those of the conventional pure TiO 2 -based DSSC, respectively. The significant improvements in the properties of the optimal DSSC are attributed to the increase of the light coupling and thus the light absorption of the dye due to the localized surface plasmon resonance of the AuNRSs.

Due to the advantages of both rapid electron transport of reduced graphene oxide (rGO) sheet and high catalytic performance of ordered mesoporous carbon (OMC), composites of OMC with rGO (G@OMC) have been prepared through the hard-template approach and used as efficient counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). When compared with pure OMC, the as-obtained G@OMC composites exhibit a higher electrocatalytic activity for the reduction of triiodide, owing to the synergetic effect between rGO and OMC. As a consequence, the DSSCs assembled with this G@OMC (CE show an improved photovoltaic conversion efficiency of 6.38% compared with 5.67% for DSSCs assembled with OMC CE, which could compete with the efficiency (7.05%) produced by the Pt CE under the same conditions.

In this paper, we prepare a composite-hierarchical microsphere (HMS) which is composed of two kinds of HMSs: one flower-like microsphere (FMS, ∼1.5 μm, containing nanoparticles and nanowires) and plentiful mesoporous submicron ellipsoidal spheres (ESs, ∼200 nm, assembled with nanoparticles) which are embedded evenly in the FMS. For comparing, pure FMS and ES are prepared, respectively. It is found that the composite-HMS possesses (a) the highest BET surface area, (b) the highest light scattering ability, (c) the fastest electron transport and the longest electron life time, and (d) light trapping ability enabled by multiple light reflection and scattering between ESs and nanowires inside each FMS*ESs particle. The energy conversion efficiency of 7.91% of the DSSC based on FMS*ESs is higher than devices based on ES and FMS (7.22% and 7.24%, respectively), which also benefits from the structural advantages of the composite-HMS compared with non-composite HMSs.

Novel yolk-shell-like TiO2 hierarchical microspheres (YSTHSs) were synthesized by a facile one-pot hydrothermal method. These YSTHSs exhibited excellent light scattering ability and high specific surface area for more dye adsorption. A YSTHSs multifunctional scattering layer was fabricated on top of a conventional TiO2 nanocrystalline layer (T) to form a heterostructure bilayer photoanode (T-YSTHS). The influences of the YSTHSs on the properties of the photoanode and dye-sensitized solar cell (DSSC) were investigated. Studies indicated that by introducing the YSTHSs, the light scattering, dye loading, electron mobility and lifetime of this bilayer photoanode were remarkably increased, resulting in the great enhancement in the short-circuit current density (Jsc) and thus the photoelectric conversion efficiency (PCE) of the DSSCs. This T-YSTHS based DSSC exhibited the maximum Jsc of 16.35 mA cm−2 and PCE of 6.01%, remarkably higher than those of the conventional TiO2 nanocrystalline (2T)-based DSSC by 27.1% and 20.4%, respectively. The remarkable enhancement in Jsc and PCE for the T-YSTHS-based DSSC compared to the 2T-based DSSCs are mainly attributed to the significant enhancement in light scattering and the increase in the specific surface area for dye adsorption due to the unique yolk-shell hierarchical microsphere structure of the YSTHSs.

A semi-closed tubular light-trapping geometry is developed for dye sensitized solar cell to stabilize its power conversion efficiency (PCE) in wide light intensity range. The tubular cell consists of a dye-sensitized porous TiO2 coated and semi-closed glass tube as photoanode, an opaque platinum metal foil wrapped on the outside of photoanode as counter electrode, and electrolyte filling in their interlayer. The open end of photoanode serves as the only light entrance. The experiment, calculation and optical studies demonstrated that the tubular geometry is beneficial to light trapping and absorption, charge transport and heat dissipation, in comparison to a planar counterpart. The PCE of tubular cell can remain about 85% of its original value even if the irradiated light intensity increases from 1 to 5 Sun, in contrast, that of planar counterpart decreases to about 60% of its original value. This feature makes the tubular cell has potential as an effective light collector in low-cost condenser solar cell system.

In this article, we in situ fabricated copper sulfide (CuS) on fluorinated tin oxide (FTO) substrate using a low temperature and low cost hydrothermal method and then organic solar cells (OSCs) were fabricated by using a thin layer of CuS film as hole transporting layer (HTL). Our CuS films, consisting of two-dimensional (2D) intersected hexagonal nanosheets, are stoichiometric and show p-type electrical conductivity, a good transparency and a high hole mobility. The Fermi level, valence and conduction band energies for CuS HTL are characterized in detail through photoelectron spectroscopy studies. The small energy barrier between the valance band of CuS and the HOMO of poly(3-hexylthiophene) (P3HT) and the high hole mobility and electrical conductivity of CuS nanosheet film benefit for the hole transporting. Therefore, CuS HTL to OSCs results in a power conversion efficiency of 3.4% with P3HT and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the active layer, which is a 13.3% increase in performance than devices with a poly (3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) HTL. Therefore, low-cost, environmental friendly and stable CuS is an appropriate choice for hole transporting materials (HTMs) in OSCs.

Hierarchical fastener-like spheres assembled from anatase TiO2 nanosheets with exposed {001} facets are successfully synthesized via a facile one-pot hydrothermal process. Compared with standard commercial P25, the as-obtained hierarchical fastener-like TiO2 spheres exhibit an improved light harvesting efficiency, owing to the excellent light scattering effect of layer-by-layer hierarchical structure and superior dye adsorption capacity of the dominant {001} facets. As a consequence, the photoanode composed of TiO2 fastener-like sphere scattering layer shows an improved DSSCs conversion efficiency of 7.01% compared to that of commercial P25 (5.78%). The remarkable electrochemical performances of hierarchical fastener-like TiO2 spheres indicate their promising application as scattering materials for DSSCs.

Graphene quantum dots (GQDs) optimized TiO 2 photoanodes and their dye-sensitized solar cells (DSSCs) were successfully demonstrated in this study for the first time. The characteristics of GQDs were confirmed by Raman and TEM measurements. Study indicated that the amount of dye-adsorption decreased firstly and then increased as the increase of the GQDs in the photoanodes, while that the J sc , V oc and η of the corresponding DSSCs increased firstly and then decreased. Of all the DSSCs, the DSSC with an optimal amount of GQDs showed the best performance with a minimum dye-adsorption while the maximum J sc of 14.07 ± 0.02 mA cm −2 and η of 6.10 ± 0.01%, higher than those of the conventional DSSC (without GQDs) by 30.9% and 19.6%, respectively. The minimum dye-adsorption while the maximum J sc and η obtained in the optimal DSSC are mainly attributed to the unique photoexcitation response of GQDs and the hot electrons injection from GQDs into TiO 2 . This study indicates that not only the properties of DSSCs can be improved by GQDs, but more importantly, the reduced use of dye by using GQDs is of significant importance for the low cost and environment-friendly DSSCs.

In-doped TiO2 thin film was introduced at the interface of fluorine-doped tin oxide (FTO) substrate and mesoporous TiO2 film by spin-coating method, and its application as a new compact layer material for dye-sensitized solar cells (DSSCs) was investigated. The scanning electron microscopy (SEM), UV-visible spectroscopy, current-voltage characteristics, Mott-Schottky analysis, electrochemical impedance spectroscopy (EIS) analysis and open-circuit voltage decay (OCVD) technique are used to characterize the morphology, optical transmittance and flat-band potentials (Vfb) of In-doped titania compact film and its effect to the photoelectron conversion process. It was found that In-doping increased the transmittance of TiO2 compact layer, the interfacial resistance between FTO substrate and porous TiO2 film and the flat-band potential of TiO2 film. The In-doped TiO2 compact layer effectively suppressed the charge recombination from FTO to the electrolyte, increased the optical absorption of dye and then increased the short-circuit photocurrent density (Jsc). Furthermore, In-doped TiO2 compact layer acted as a weak energy barrier, which increased the electron density in the mesoporous TiO2 film, thus improved open-circuit photovoltage (Voc). As a result, the overall energy conversion efficiency of the DSSC with In-doped TiO2 compact layer was enhanced by 11.9% and 6.9% compared to the DSSC without compact layer and with pure TiO2 compact layer, respectively. It indicated that In-doped TiO2 is a promising compact layer material for dye-sensitized solar cells.

Highly uniform, monodisperse β-NaYF4:Yb3+/Er3+(NYFYE) up-conversion phosphor submicron hexagonal prisms coated with a SiO2 layer are synthesized via a hydrothermal route, forming a core–shell NYFYE@SiO2 crystallites. These crystallites are incorporated into TiO2 nanocrystalline porous film to act as a bifunctional layer and form a composite photoanode employed in dye-sensitized solar cells (DSSCs). The influences of different amount of the NYFYE@SiO2 on the performance of the composite photoanodes and DSSCs are investigated. Studies indicate that by adding NYFYE@SiO2 the light scattering, absorption and near-infrared light harvesting of the composite photoanode are significantly increased, resulting in the great enhancement in the short-circuit current density (Jsc) and photoelectric conversion efficiency (η) of the DSSCs. The optimal properties with an Jsc of 14.91 mA cm−2 and η of 7.28% are obtained in a DSSC with NYFYE@SiO2 content of 15 wt %, increasing significantly by 14% and 29%, respectively, in comparison with those of the DSSC with pure TiO2 photoanode. This significant enhancement in the performance of the DSSCs can be attributed to the enhanced light absorption due to the enhanced light scattering and near-infrared up-conversion of the NYFYE@SiO2 bifunctional layer in the photoanode of the DSSCs.

Graphene-composited TiO2 photoelectrodes are prepared by hydrothermal method. The influences of different amount of graphene on the structures and properties of the dye-sensitized solar cells (DSSCs) are studied and an optimal graphene-composited DSSC is obtained. Studies indicate that compositing of graphene can effectively enhance the open circuit voltage, short circuit current density, and photoelectric conversion efficiency (η) of the DSSCs. Furthermore, the η of the DSSC with the optimal graphene-composited TiO2 film is 7.02 ± 0.06%, significantly higher than that of the pure TiO2 DSSC. These improvements can be attributed to the increased dye absorption due probably to the increase of the photoelectrode films’ specific surface area and the good conductivity of graphene.

Copper sulfide (CuS) with nanosheet structure has been synthesized at a low temperature in situ on copper (Cu) film coated fluorine-doped tin oxide glass and bifacial quantum dot-sensitized solar cells (QDSSCs) were herein developed by using these CuS as counter electrodes (CEs). CuS is an environmental compatible and low toxic material. The obtained two-dimensional CuS nanosheet film presents high carrier mobility and exhibits highly catalytic performance for the polysulfide-based electrolyte. The QDSSC based on a CuS CE presents a power conversion efficiency (PCE) of 3.65% by optimizing the thickness of the Cu film under front illumination. The QDSSC based on a CuS CE prepared with a 200 nm thick Cu film shows a very close PCE under front and rear illuminations in which the values are as high as 2.70% and 2.40%, respectively. All the PCEs of the CuS CEs are much higher than that of the Pt CE (1.34%).

A TiO2-embedded NiCl2 gel is prepared and used as growth catalyst to in situ synthesize binded, thick and porous carbon nanoparticles (CNPs) on Ti foil substrate with a simple flame synthesis method for dye sensitized solar cell (DSSC) counter electrode (CE) applications. The viscous gel catalyst can hold sufficient NiCl2 coated on substrate to make CNP layer thick. The embedded TiO2 can effectively separate the abundant NiCl2 components to active the Ni catalyst for CNP growth and then make CNP layer become porous. In addition, the TiO2 components can bind the porous CNP products to make them conductive. With an optimized TiO2 fraction, the CE shows high catalytic ability and electrical conductivity. By applying this CNP CE for DSSC, a photovoltaic conversion efficiency of 6.6% is achieved, which exceeds 6.5% of a reference cell using costly platinum as CE. Furthermore, the CNP structure is demonstrated beneficial to carrier transport by a mass transfer model. This easy and effective preparation method may have a potential application in general nanomaterial preparation.

Piezoelectric nanogenerators (PENGs) based on highly aligned poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] nanofibers and micropatterned three-dimensional (3D) interdigital electrodes with good flexibility and highly output performance are constructed. The optimal PENG with 3D interdigital electrodes could charge the commercial capacitor of 100 nF to 3.2 V under the pressure of 2 kPa at a frequency of 1.5 Hz, which is nearly 10-fold higher than that of PENG with flat interdigital electrodes. The enhanced performance is mainly attributed to micropatterned 3D interdigital electrodes that could simultaneously optimize output voltages and currents of PENGs. And maximum power density of the optimal PENG could reach as high as 8.75 μW/cm2, which is superior to some PENGs based on PVDF and its copolymers. In addition, the optimal PENG generates a voltage as high as 150 V during fingers pressure/release cycles, the outputs could light up 32 light-emitting diodes after direct-current rectification. The flexible PENG can also be used to harvest the biomechanical energy of human movements, such as fingers tapping, walking, and jumping. The designed 3D interdigital electrodes represent a novel strategy to improve the performance of PENGs based on aligned nanofibers. This kind of PENG shows potential as an energy harvester and effective self-powered nanogenerator to drive wearable devices.

Light harvesting in dye-sensitized solar cells (DSSCs) mediated by plasmonic metallic nanoparticles and sub-micron light-scattering metal oxides is a facile and cost-effective approach to achieving high device performance. Ag nanoparticles, protected by thin shells of TiO2, were incorporated in TiO2 photoanode. The large plasmonic near-field intensity generated by these nanoparticles caused an 18.3% rise in photocurrent, which resulted in an enhanced efficiency of 6.23% as compared to 5.29% efficiency of DSSC based on unmodified TiO2 photoanode. In addition, DSSC with TiO2 nanofibers (NFs) embedded in TiO2 photoanode was also constructed, which because of the efficient light scattering ability of the nanofibers, attained an efficiency of 7.14% as a result of a current rise of 36.9%. Another DSSC was assembled with Ag NPs added to the photoanode of the NFs-based DSSC to further boost cell performance. The addition of Ag NPs, however, did not produce an appreciable change in the cell performance. The reason for this unexpected outcome was probably due to the low internal resistance associated with charge recombination and large resistance to electron transport in the cell as determined by electrochemical impedance analysis computed in this work.