Surface doping is being used as an effective approach to improve the mechanical, optical, electronic, and magnetic properties of various materials. For example, experimental studies have proven that rare-earth element doping can enhance the optical properties of silicon nanostructures. However, the majority of previous investigations focused on either bulk materials or nanosized spherical crystals. Here we present a comparative study on semiconducting germanium (Ge) nanowires with and without surface doping by using multiple integrated characterization probes, including high resolution scanning/transmission electron microscopy (SEM/TEM), in situ high pressure synchrotron X-ray diffraction (XRD), and Raman spectroscopy. Our results reveal that under pressure the stability of the Ge-I phase (diamond structure) in erbium (Er)-doped Ge nanowires is enhanced compared to undoped Ge nanowires. We also found an increased stability of the Ge-II phase (body centered tetragonal structure) in Er-doped Ge nanowires during decompression. Furthermore, the presence of Er doping elevates the transition kinetics by showing a smaller pressure span needed for a complete Ge-I to Ge-II phase transformation. In contrast, Er doping has a negligible impact on the mechanical properties of Ge nanowires under high pressure, exhibiting a very different mechanical behavior from other foreign element-doped nanostructures. This anomalous doping effect was explained based on surface modification and decoration. These findings are of both fundamental and applied significance, because they not only provide a thorough understanding of the distinct role of surface doping in nanoscale materials, but also yield insight with regard to a given material’s design for favorable properties in semiconductor nanostructures.

Bandgap engineering of kesterite Cu2Zn(Sn, Ge)(S, Se)4 with well-controlled stoichiometric composition plays a critical role in sustainable inorganic photovoltaics. Herein, a cost-effective and reproducible aqueous solution-based polymer-assisted deposition approach is developed to grow p-type Cu2Zn(Sn, Ge)(S, Se)4 thin films with tunable bandgap. The bandgap of Cu2Zn(Sn, Ge)(S, Se)4 thin films can be tuned within the range 1.05–1.95 eV using the aqueous polymer-assisted deposition by accurately controlling the elemental compositions. One of the as-grown Cu2Zn(Sn, Ge)(S, Se)4 thin films exhibits a hall coefficient of +137 cm3/C. The resistivity, concentration and carrier mobility of the Cu2ZnSn(S, Se)4 thin film are 3.17 ohm·cm, 4.5 × 1016 cm–3, and 43 cm2/(V·S) at room temperature, respectively. Moreover, the Cu2ZnSn(S, Se)4 thin film when used as an active layer in a solar cell leads to a power conversion efficiency of 3.55%. The facile growth of Cu2Zn(Sn, Ge)(S, Se)4 thin films in an aqueous system, instead of organic solvents, provides great promise as an environmental-friendly platform to fabricate a variety of single/multi metal chalcogenides for the thin film industry and solution-processed photovoltaic devices.Keywords: bandgap tunable; CZTGeSSe; polymer-assisted deposition; solar cells; solution processing;

The underlayer plays an important role for organic–inorganic hybrid perovskite formation and charge transport in perovskite solar cells (PSCs). Here, we employ a classical organic small molecule, 5,6,11,12-tetraphenyltetracene (rubrene), as the underlayer of perovskite films to achieve 15.83% of power conversion efficiency with remarkable moisture tolerance exposed to the atmosphere. Experiments demonstrate rubrene hydrophobic underlayer not only drives the crystalline grain growth of high quality perovskite, but also contributes to the moisture tolerance of PSCs. Moreover, the matching energy level of the desirable underlayer is conductive to extracting holes and blocking electrons at anode in PSCs. This introduction of organic small molecule into PSCs provides alternative materials for interface optimization, as well as platform for flexible and wearable solar cells.Keywords: organic small molecule; planar perovskite solar cells; rubrene; underlayer;

In this letter, we report a facile self-foaming strategy to synthesize Ni3C nanoparticles embedded in a porous carbon network (Ni3C@PCN) by rationally incorporating a nickel salt precursor into the carbon source. As a novel hydrogen evolution reaction (HER) catalyst, the Ni3C@PCN shows superior catalytic activity with an onset potential of −65 mV, an overpotential of 262 mV to achieve 50 mA cm–2 current density, a Tafel slope of 63.4 mV/dec, and durability over 12 h in acidic media. The excellent performance of the novel 3D composite material along with its low-cost merits is suggestive of great potential for scalable electrocatalytic H2 production.Keywords: carbon network; composites; electrocatalyst; hydrogen evolution; Ni3C;

High-performance electrocatalysts for water splitting at all pH values have attracted considerable interest in the field of sustainable hydrogen evolution. Herein, we report an efficient electrocatalyst with a nanocrystalline cobalt phosphide (CoP) network for water splitting in the pH range of 0–14. The novel flexible electrocatalyst is derived from a desirable nanocrystalline CoP network grown on a conductive Hastelloy belt. This kind of self-supported CoP network is directly used as an electrocatalytic cathode for hydrogen evolution. The nanocrystalline network structure results in superior performance with a low onset overpotential of ~45 mV over a broad pH range of 0 to 14 and affords a catalytic current density of 100 mA·cm−2 even in neutral media. The CoP network exhibits excellent catalytic properties not only at extreme pH values (0 and 14) but also in neutral media (pH = 7), which is comparable to the behavior of state-of-the-art platinum-based metals. The system exhibits an excellent flexible property and maintains remarkable catalytic stability during continuous 100-h-long electrolysis even after 100 cycles of bending/extending from 100° to 250°.

Exploring low-cost and efficient electrocatalysts based on earth-abundant elements for the hydrogen evolution reaction (HER) is of great importance for the development of clean and renewable energy. In this work, we report a facile self-foaming strategy for synthesis of hierarchically interconnected nitrogen-doped carbon nanosheets (NCNS). The doping N species within the 3D interconnected carbon network affords rich active sites for the HER and facilitates fast charge transfer. As a result, the NCNS exhibit excellent catalytic activity with an onset potential of −65 mV, and a Tafel slope of 81 mV dec−1 with robust stability over 10 h in acidic media. Further analyses suggest that the graphitic N species in the NCNS contribute to their catalytic activity. Such a high catalytic performance makes the NCNS a promising metal-free HER electrocatalyst for practical hydrogen production.

One of the primary challenges for high-quality metal chalcogenide film growth by a chemical solution approach is to avoid the use of volatile/hazardous organic solvents during the fabrication processes. Herein, we demonstrate an organic solvent-free solution processing method which has the ability to enable growth of a diverse range of metal chalcogenide films. The processing solution is prepared by combining the required metal ions with non-volatile and non-flammable ionic liquid precursor solutions. These stable and homogeneous solutions can form a variety of high-quality and uniform metal chalcogenide films. Due to the facile and instant control of the stoichiometry used in this method, the band gap of multi-element compound semiconductors, for example quinary Cu2ZnSn(S,Se)4, can be easily tuned from 1.01 eV of Cu2ZnSnSe4 to 1.52 eV of Cu2ZnSnS4. The resulting film also shows high hole mobility with a maximum of 56.9 cm2 V−1 s−1 for a carrier concentration of 3.24 × 1016 cm−3 at room temperature. Cu2ZnSnS4-based solar cells displayed an efficiency of 5.68%, which is comparable to the reported efficiencies of solar cells prepared by methods involving organic solvents (5.0–6.4%).

Interface engineering is an efficient method for improving the performance of planar perovskite solar cells (PSCs). In this paper, the performance of PSCs was improved significantly by introducing 4,7-diphenyl-1,10-phenanthroline (Bphen) doped with bis(2-methyldibenzo-[f,h]quinoxaline) (Ir(MDQ)2(acac)) to modify the interface between perovskite (CH3NH3PbI3−xClx)/PCBM (phenyl-C61-butyric acid methyl ester) and an Ag electrode. The power conversion efficiency (PCE) was enhanced up to 15.87%, compared with 10.77% for the reference device without interlayer modification. It was found that the enhanced PCE was attributed to the better interface contact between the perovskite and Ag cathode. A suitable interface roughness is beneficial for reducing the leakage current and the probability of carrier recombination, resulting in an enhanced fill factor and thus improved device efficiency.

Neutral green-emitting four-coordinate Cu(I) complexes with general formula POPCu(NN), where POP = bis[2-(diphenylphosphino)phenyl]ether and NN = substituted 2-pyridine-1,2,4-triazole ligands, were synthesized. The crystal structures of (POPCuMeCN)+(PF6)− (1), POPCuPhPtp (2a, PhPtp = 2-(5-phenyl-2H-[1,2,4]triazol-3-yl)-pyridine), and POPCu(3,5-2FPhPtp) (2d, 3,5-2FPhPtp = 2-(5-(3,5-difluorophenyl)-2H-1,2,4-triazol-3-yl)pyridine) were determined by single-crystal X-ray diffraction analysis. The electronic and photophysical properties of the complexes were examined by UV–vis, steady-state, and time-resolved spectroscopy. At room temperature, weak emission was observed in solution, while in the solid state, all complexes exhibit intense green emission with quantum yield up to 0.54. The electronic and photophysical properties were further supported by calculation performed at the (time-dependent) density functional theory level. One of the complexes was also tested as dopant in electroluminescent devices.

A light-scattering cyanobiphenyl derivative 6-[(4'-cyano(1,1'-biphenyl)-4-yl)oxy]he-xanoic acid (CBHA) was designed, synthesized and applied as a co-adsorbent for dye-sensitized solar cells. The effect of CBHA on the light absorption and reflectance of dyed-TiO2 photoanodes was investigated in detailed. It revealed that a certain amount of CBHA adding to dye Z907 could obviously increase the light absorption of TiO2 photoanodes by decreasing the dye loading amount and possibility of aggregation. Meanwhile, light-scattering property of CBHA rendered their TiO2 photoanodes higher light-harvesting efficiency. In addition, electrochemical impedance spectroscopy results indicated that CBHA could restrain the interfacial electron recombination for longer life time. Thus, a performance improvement of ∼0.81% from 5.23% to 6.04% could be obtained by the resulting device employing CBHA. Moreover, the DSSCs with CBHA also display better stability than the referenced devices. This novel light-scattering co-absorbent offers us a feasible strategy to design multiple functional co-adsorbents for high performance dye-sensitized solar cells.

Three simple imidazolium-type ionic liquids with benzene cores (abbreviated as [TMImB][Br] and [TMImB][TFSI]) have been successfully designed, synthesized and characterized. The chemical structure, thermal and electrochemical properties have also been investigated in detail. Moreover, it is revealed that adding 20 wt% [TMImB][TFSI] could effectively suppress the crystal growth of the typical ionic conductor 1-ethyl-3-methylimidazolium iodide (EMII). Meanwhile, [TMImB][TFSI] can facilitate the EMII-based solid-state electrolyte to form a much smoother surface morphology than EMII alone, which can improve interfacial electrochemical contact among EMII and porous TiO2 films. Therefore, the resultant solid-state DSSC with [TMImB][TFSI] exhibits a higher efficiency of 5.66% than the DSSC without crystal growth inhibitors, and displays better long-term stability than the DSSC with conventional EMIBF4. These preliminary results provide us with more opportunities to explore new crystal growth inhibitors with special chemical structures for high performance ssDSSCs.

•An aqueous solution route is developed for transparent conducting carbon film.•Introducing Cu catalyzer can enhance the conductivity of the carbon film.•Carbon film can be easily deposited on flexible substrate owing to the precursor's excellent forming ability and permeability.We report an aqueous solution route for directly depositing transparent carbon thin film on SiO2 substrate using polyethyleneimine as carbon precursor. The conductivity of the carbon thin film is calculated to be ~1500 S/cm. Benefiting from film forming ability and permeability of PEI, homogenous and smooth carbon thin films can be deposited onto the quartz substrate with different shapes (e.g. flexible quartz fibers). Investigation finds that additional Cu ions in the precursor could prevent the decomposition and evaporation of PEI to help the graphitization of carbon thin film. Moreover, the Cu ions aggregating to Cu nanoparticles significantly enhance the absorption of carbon thin film, which may advance the application of carbon thin film in surface plasmon resonance.A catalyst/transfer free route is employed to grow the transparent conducting carbon film on SiO2 substrate/fiber in polymer-assisted aqueous solution. Extra Cu ions bound to polyethyleneimine facilitate the formation of the partially graphitized ultra-thin carbon film. The conductivity of the carbon film is calculated to be ~1500 S /cm.

A novel crown ether lithium salt complex [Li∈12-C-4][I] has been designed, synthesized and characterized. The thermal properties of the [Li∈12-C-4][I] based solid-state electrolytes were also investigated in detail. The particular trapping ability of 12-crown-4 to Li+ can obviously reduce the cation–anion (Li+–I−) interaction and hence facilitate favorable electrical properties of the solid-state electrolytes. Therefore, [Li∈12-C-4][I] represents ionic conductivity of 3.93 × 10−5 and 1.53 × 10−4 S cm−1 at 25 and 80 °C, respectively. Further addition of the ionic liquid 1-propyl-3-methylimidazolium iodine as a crystal growth inhibitor can effectively suppress the crystallization of the complex for more amorphous and smoother regions, which are much more conducive towards higher ion conductivity by the segmental motion of molecule chains. For application, the resulting device showed a power conversion efficiency of 5% and displayed excellent long-term stability. These results offer us more opportunities to explore simple and novel solid-state electrolytes for energy storage and conversion.

In this study, we report the growth of molybdenum oxide (MoOx) film by polymer-assisted deposition (PAD), an environmentally friendly strategy in an aqueous system. The MoOx film has good crystal quality and is dense and smooth. The transparency of the film is >95% in the wavelength range of 300–900 nm. The device based on P3HT:PCBM absorber material was fabricated. The solar cell with PAD-MoOx as an anode interfacial layer exhibits great performance, even better than that of a solar cell with PEDOT:PSS or evaporated MoOx as an anode interfacial layer. More importantly, the solar cells based on the growth of MoOx have a longer term stability than that of solar cells based on PEDOT:PSS. These results demonstrate the aqueous PAD technology provides an alternative strategy not only for the thin films’ growth of applied materials but also for the solution processing for the low-cost fabrication of future materials to be applied in the field of solar cells.Keywords: anode interfacial layer; molybdenum oxide; polymer-assisted deposition; solar cell

Carbon nanotubes (CNTs) embedding organic ionic plastic crystals electrolytes were prepared and characterized by thermal analysis and scanning electron microscopy to investigate the influence of CNTs contents on the thermal properties and surface morphology. The investigation showed the addition of CNTs had little effect on the melting points and solid–solid phase transition properties of the plastic crystals electrolytes. However, with CNTs increasing, the solid-state electrolytes produced more defected/amorphous regions, resulting in better ionic conductivity and diffusion coefficients of I− and I3−. Furthermore, based on these solid-state electrolytes, the resulting solid-state dye-sensitized solar cell exhibited maximal power conversion efficiency of 5.60%, and displayed much more excellent long-term stability than that of referenced ionic liquids-based device. These results offer us a feasible method to develop more excellent plastic crystals electrolytes for high performance solid-state dye-sensitized solar cells.

The controllable synthesis of strongly coupled inorganic materials/carbon nanotubes (CNTs) hybrids represents a long-standing challenge for developing advanced catalysts and energy-storage materials. Here we report a simple sol-gel method for facile synthesis of TiO2/CNTs hybrid. The porous anatase TiO2 nanoparticles are uniformly coated on the CNTs conducting network, which leads to remarkably improved electrochemical performances such as exceptional cycling stability, good high rate durability, and reduced resistance. This hybrid exhibits a reversible capacity as high as 200 mA·h g−1 at a current density of 0.1 A g−1 as an anode in lithium-ion battery (LIB). As a supercapacitor (SC), it shows a specific supercapacitance of 145 F g−1 in 0.5 M H2SO4 electrolyte, higher than that of the previously reported TiO2 based supercapacitors. Moreover, this hybrid also exhibits excellent durability after 1000 cycles for both LIBs and SCs. Such superior performance and cycling durability demonstrate the reinforced synergistic effects between the porous TiO2 and interweaved CNTs network, indicating a great application potential for such hybrid materials in high power LIBs and SCs.

A novel crown ether functionalized ionic liquid has been designed, synthesized and characterized in detail. The thermal properties of the ionic liquid are also investigated. When LiI or MgI2 is introduced into the ionic liquid at the same concentration of the metal cations, the particular trapping ability of the crown ether to metal cations could effectively reduce the electrostatic interaction between the metal cations and iodide anions to release more iodide anions. Electrochemical impedance analysis reveals that ∼35 fold of ionic conductivity enhancement for the multi-iodine doped ionic liquids can be obviously observed at room temperature. For applications, these multi-iodine doped crown ether functionalized ionic liquids can be used as gel electrolytes for dye-sensitized solar cells, displaying a power conversion efficiency of 3.86% at a simulated AM1.5 solar spectrum illumination at 100 mW cm−1. These preliminary results provide us with a feasible strategy to enhance the ionic conductivity and explore new ionic liquid electrolytes for energy storage and conversion devices.

Highly fluorescent nitrogen-doped graphitic carbon dots (NGCDs) are developed as new label-free chemosensors for gallium ion (Ga3+) detection for the first time. Through the pyrolysis of ammonium citrate in air, NGCDs have been prepared with high fluorescence quantum yield (FLQY: 44.8%). As-prepared NGCDs exhibit excellent photostability under continuous UV irradiation. Owing to the strong interaction between Ga3+ and the oxygen functional groups (e.g., hydroxyl, carboxyl), the fluorescent NGCDs chemosensor shows a highly sensitive and selective response (a detection limit of 209 nM) to Ga3+ in a wide concentration range of 0–20 μM. Further fluorescence lifetime analyses suggest the quenching mechanism appears to be a dynamic process.

Transparent p-type nickel oxide (NiO) thin films have been epitaxially grown on (0001) Al2O3 substrates by a chemical solution method of polymer-assisted deposition for the first time. The films have a high optical transparency of above 95% in the wavelength range of 350–900 nm.

Two-dimensional V2O5 and manganese-doped V2O5 sheet network were synthesized by a one-step polymer-assisted chemical solution method and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal-gravimetric analysis, and galvanostatic discharge–charge analysis. The V2O5 particles were covered with thin carbon layers, which remained after decomposition of the polymer, forming a network-like sheet structure. This V2O5 network exhibits a high capacity of about 300 and 600 mA·h/g at a current density of 100 mA/g when it was used as a cathode and anode, respectively. After doping with 5% molar ratio of manganese, the capacity of the cathode increases from 99 to 165 mA·h/g at a current density of 1 A/g (∼3 C). This unique network structure provides an interconnected transportation pathway for lithium ions. Improvement of electrochemical performance after doping manganese could be attributed to the enhancement of electronic conductivity.Keywords: conductivity; lithium-ion battery; manganese-doped; polymer-assisted solution method; V2O5 network

Direct growth of mesoporous TiO2 on Ni foam via a one-step soft template synthesis was directly used for a binder-free anode for lithium-ion batteries. The mesoporous TiO2 with a high specific surface area of 158.8 m2 g−1 and average pore size of 5.4 nm formed network-like sheets on the surface of the Ni foam. The binder-free TiO2/Ni anode shows improved electrochemical performance with a capacity as high as 341 mA h g−1 at a current density of 100 mA g−1 after 10 cycles and 82.4 mA h g−1 at a current density of 1000 mA g−1 after 30 cycles. The enhanced electrochemical performance is attributed to the mesoporous structure that shortens the lithium ion diffusion path and facilitates the transport of lithium ions.

In this tutorial article, the recent development of polymer assisted deposition (PAD) for the growth of a wide range of materials, in particular in thin films, is reviewed. Specifically, we describe the unique chemistry and processes of PAD for the deposition of metals, metal–oxides, metal–nitrides, metal–carbides, and their derived composites. Many examples are given not only to illustrate the powerfulness of PAD for high quality coatings, but also to give readers an opportunity to evaluate this technique for specific applications. The challenging issues related to PAD, based on the authors' experience, are also discussed in this review article.

We report the synthesis of carbon nanotube/TiC hybrid fibers using a polymer-assisted chemical solution approach. Ti metal ions are bound to aqueous polyethyleneimine (PEI) to form precursor solution. Amphiphilic PEI with Ti easily permeates the CNT fibers. Upon annealing in a controlled atmosphere, a homogeneous TiC network is formed in the CNT fibers. The obtained CNT/TiC hybrid fibers show prominent enhancement in mechanical strength and electrical conductivity. The tensile strength and conductivity of CNT/TiC fibers can be improved to 0.67 GPa and 1650 S cm−1 at room temperature, respectively. More importantly, a tensile modulus as high as 420 GPa has been achieved for the CNT/TiC fibers. Analysis shows that the cross-linking matrix of hard TiC plays a significant role in the improvement of mechanical strength. Furthermore, the electrons are transported in the CNT/TiC fiber by a three dimensional hopping mechanism.

An efficient dual catalyst of molybdenum carbide nanoparticles embedded nitrogen-doped porous carbon nanofibers (Mo2C/NPCNFs) has been developed for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The well-aligned and nanoporous identity of the desirable hybrid Mo2C/NPCNFs by an electrospun approach provides the good conductivity and rich active sites addressing excellent HER catalytic performance with an onset potential of −85 mV, a Tafel slope of 68 mV dec−1, and an exchange current density of 0.178 mA cm−2 in 0.5 M H2SO4. It is noting that the Mo2C/NPCNFs also shows remarkable ORR catalytic activity with an onset potential of ∼0.9 V, a half-potential of ∼0.77 V and a Tafel slope of 60.2 mV dec−1 at 1600 rpm in 0.1 M KOH. In addition, the experimental results demonstrate the core-shell 1D nanostructures boost the Mo2C/NPCNFs' stability of the durable catalytic activity over 10 h for both HER and ORR. This study designs a new structure for carbon-supported Mo2C composites, providing a distinctive course for the development of high-performance non-noble HER and ORR catalysts.

Transparent p-type nickel oxide (NiO) thin films have been epitaxially grown on (0001) Al2O3 substrates by a chemical solution method of polymer-assisted deposition for the first time. The films have a high optical transparency of above 95% in the wavelength range of 350–900 nm.

In this tutorial article, the recent development of polymer assisted deposition (PAD) for the growth of a wide range of materials, in particular in thin films, is reviewed. Specifically, we describe the unique chemistry and processes of PAD for the deposition of metals, metal–oxides, metal–nitrides, metal–carbides, and their derived composites. Many examples are given not only to illustrate the powerfulness of PAD for high quality coatings, but also to give readers an opportunity to evaluate this technique for specific applications. The challenging issues related to PAD, based on the authors' experience, are also discussed in this review article.

A novel crown ether lithium salt complex [Li∈12-C-4][I] has been designed, synthesized and characterized. The thermal properties of the [Li∈12-C-4][I] based solid-state electrolytes were also investigated in detail. The particular trapping ability of 12-crown-4 to Li+ can obviously reduce the cation–anion (Li+–I−) interaction and hence facilitate favorable electrical properties of the solid-state electrolytes. Therefore, [Li∈12-C-4][I] represents ionic conductivity of 3.93 × 10−5 and 1.53 × 10−4 S cm−1 at 25 and 80 °C, respectively. Further addition of the ionic liquid 1-propyl-3-methylimidazolium iodine as a crystal growth inhibitor can effectively suppress the crystallization of the complex for more amorphous and smoother regions, which are much more conducive towards higher ion conductivity by the segmental motion of molecule chains. For application, the resulting device showed a power conversion efficiency of 5% and displayed excellent long-term stability. These results offer us more opportunities to explore simple and novel solid-state electrolytes for energy storage and conversion.

Interface engineering is an efficient method for improving the performance of planar perovskite solar cells (PSCs). In this paper, the performance of PSCs was improved significantly by introducing 4,7-diphenyl-1,10-phenanthroline (Bphen) doped with bis(2-methyldibenzo-[f,h]quinoxaline) (Ir(MDQ)2(acac)) to modify the interface between perovskite (CH3NH3PbI3−xClx)/PCBM (phenyl-C61-butyric acid methyl ester) and an Ag electrode. The power conversion efficiency (PCE) was enhanced up to 15.87%, compared with 10.77% for the reference device without interlayer modification. It was found that the enhanced PCE was attributed to the better interface contact between the perovskite and Ag cathode. A suitable interface roughness is beneficial for reducing the leakage current and the probability of carrier recombination, resulting in an enhanced fill factor and thus improved device efficiency.