Electron Diffusion Length Research Articles

CuO/NiOx thin film–based photocathodes for photoelectrochemical water splitting

Copper oxides are considered to be very promising materials for promoting a hydrogen evolution reaction (HER). However, some CuO features, such as the recombination of charge carriers, electron diffusion length, and the chemical stability need to be improved. In this work, NiOx was studied as co-catalyst to FTO/CuO, and the films were physically characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The photo-electrochemical activity and stability toward the HER were evaluated by depositing films on fluorine-tin doped oxide (FTO) substrate. Although, the CuO (− 3.61 eV) and NiOx (− 1.13 eV) conduction band positions, estimated by UV-Vis diffuse reflectance and the Mott–Schottky measurements, did not allow electronic transfer from CuO to NiOx, the formation of a thin layer of NiOx on CuO was beneficial for the activity of this material. The best CuO/NiOx film exhibited a photocurrent density of − 1.02 mA cm−2 at 0 V vs. RHE, which was higher than that for CuO (− 0.92 mA cm−2). A mechanism of electron transfer between CuO and NiOx is proposed. The absorption of visible light by CuO leads to the generation of electron-hole pair. Part of the photogenerated electrons are trapped by the NiOOH present in the NiOx layer, as demonstrated by XPS. The oxy-hydroxide is reduced to metallic Ni, and this species acts as a catalyst for the hydrogen evolution reaction. Due to the increase in interfacial pH caused by the evolution reaction of H2, the formed metallic Ni can be regenerated to NiOx.

High‐Efficiency Low‐Temperature‐Processed Mesoscopic Perovskite Solar Cells from SnO2 Nanorod Self‐Assembled Microspheres

Mesoporous scaffolds in perovskite solar cells (PSCs) can accelerate the formation of heterogeneous nucleation sites, leading to enhanced quality of perovskite films and uniform perovskite coverage over large areas. Nevertheless, the mesoporous electron transport layers (ETLs) can effectively compensate for the drawback of shorter electron diffusion lengths than their hole counterparts. Therefore, most mesoscopic PSCs usually show superior photovoltaic performance to their planar counterparts. However, mesoporous ETLs, particularly those prepared with metal oxide nanocrystals, often require a high‐temperature sintering process for the removal of residual organics and the improved crystallization of metal oxides. Here, a novel emulsion‐based bottom‐up self‐assembly strategy is used to prepare sizable SnO2 microspheres from oleic acid capped SnO2 nanorods. Combined with an in‐situ ligand‐stripping strategy, the low‐temperature solution‐processed mesoscopic PSCs can achieve efficiency as high as 21.35% with slight hysteresis and good reproducibility. In particular, the emulsion‐based bottom‐up self‐assembly strategy is a general way for preparing microspheres from several kinds of semiconductor nanocrystals, so it will greatly expand the material selection range for preparing efficient mesoscopic PSCs and even inverted mesoscopic devices.

Niobium doped TiO2 nanorod arrays as efficient electron transport materials in photovoltaic

One-dimensional (1-D) rutile TiO2 nanorod arrays (NRAs) synthesized by a hydrothermal method suffer from low electrical conductivity and large amounts of surface defects, hindering their further applications. Nb doping is thus introduced to modify their electronic properties. Results indicate that light Nb doping reduces rod nanosizes, increases electron concentrations, decreases surface defective oxides and lowers conduction band of the TiO2 NRAs, while heavy doping induces transformations of morphologies and crystalline orientations as well as occurrences of compositional deviations and low oxidative states of Ti3+. After 0.1 mol% and 1 mol% Nb incorporations, device efficiencies are substantially improved by ~16% and ~33% for the model perovskite and dye-sensitized solar cells, respectively, which are ascribed to reduced recombination at the perovskite/TiO2 interfaces (e.g. charge lifetime increasing from 62 μs to 107 μs) and improved electron transport through the photoanode of TiO2 NRAs (e.g. electron diffusion length increasing from ~14 μm to ~50 μm). Our study verifies that Nb doped 1-D TiO2 NRAs are versatile electron transporting materials in different kinds of emerging solar cells, and are also potential for other fields including photocatalysis, sensors and batteries etc.

Sodium/Potassium-Ion Batteries: Boosting the Rate Capability and Cycle Life by Combining Morphology, Defect and Structure Engineering.

Carbon-based materials have been considered as the most promising anode materials for both sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs), owing to their good chemical stability, high electrical conductivity, and environmental benignity. However, due to the large sizes of sodium and potassium ions, it is a great challenge to realize a carbon anode with high reversible capacity, long cycle life, and high rate capability. Herein, by rational design, N-doped 3D mesoporous carbon nanosheets (N-CNS) are successfully synthesized, which can realize unprecedented electrochemical performance for both SIBs and PIBs. The N-CNS possess an ultrathin nanosheet structure with hierarchical pores, ultrahigh level of pyridinic N/pyrrolic N, and an expanded interlayer distance. The beneficial features that can enhance the Na-/K-ion intercalation/deintercalation kinetic process, shorten the diffusion length for both ions and electrons, and accommodate the volume change are demonstrated. Hence, the N-CNS-based electrode delivers a high capacity of 239 mAh g-1 at 5 A g-1 after 10 000 cycles for SIBs and 321 mAh g-1 at 5 A g-1 after 5000 cycles for PIBs. First-principles calculation shows that the ultrahigh doping level of pyridinic N/pyrrolic N contributes to the enhanced sodium and potassium storage performance by modulating the charge density distribution on the carbon surface.

Electrochemical performance of a self-assembled two-dimensional heterostructure of rGO/MoS2/h-BN.

We report the preparation and electrochemical performance evaluation of a two-dimensional (2D) self-assembled heterostructure of graphene oxide (rGO), molybdenum disulphide (MoS2), and hexagonal boron nitride (h-BN). In the present study, the rGO–MoS2–h-BN (GMH) multi-layered GMH heterostructure is fabricated via an in situ chemical route. Based on material analysis, the composite consists of bond conformations of C–B–C, Mo–S, C–N, B–N, and Mo–C, indicating the layered stacks of rGO/h-BN/MoS2. In electrochemical analysis, the composite showed superior performance in the aqueous medium of cobalt sulphate (CoSO4) over other samples. CV measurements, performed over the range 10 to 100 mV s−1, showed a change in specific capacitance (Csp) from 800 to 100 F g−1. GMH showed almost no degradation up to 20 000 cycles @ 100 mV s−1. The calculated Csp, energy density (ED), and power density (PD) are discussed in light of Nyquist, Bode, and Ragone analysis. An equivalent circuit is simulated for the cell and its discrete electronic components are discussed. Due to its larger effective electron diffusion length > 1000 μm, broadly, the composite showed battery-like characteristics, as supported by radical paramagnetic resonance and transport response studies. The symmetric electrodes prepared in one step are facile to fabricate, easy to integrate and involve no pre or post-treatment. They possess superior flat cell character, are cost effective, and are favourable towards practicality at an industrial scale, as demonstrated on the laboratory bench. The details are presented.

Influence of secondary electron emission characteristic of dielectric materials on microwave breakdown

For a microwave device filled with dielectrics, the secondary electron (SE) emission has a very important influence on the mechanism of microwave breakdown including low pressure discharge and multipactor. In this work, the SE yields (SEYs) and the SE energy spectra of seven kinds of dielectric materials are first measured and then used to examine their effects. In the positive charging process under electron irradiation, the surface potential of the dielectric layer trends to be steady with the SEY being one. Based on the measurement data, the steady surface potential is calculated under the charging stability condition. The steady surface potential is bigger for a bigger SEY. For a given SEY, the steady surface potential is found to be proportional to the peak energy <i>E</i><sub>peak</sub> of the SE energy spectrum. Furthermore, the effect of steady surface potential on low pressure discharge and multipactor are respectively studied for a parallel plate system filled with a dielectric layer. A static electric field related to the positive charging is introduced. The electron diffusion model in low pressure discharge process is modified by considering the static electric field. The electrons drift in a fixed direction under the action of static electric field, and the electron diffusion length decreases. Consequently, the effective electrons for low discharge decreases and the threshold microwave power increases. Therefore, a dielectric material with higher SEY and bigger <i>E</i><sub>peak</sub> is helpful in suspending the inhibition of low pressure discharge. Furthermore, the effect of steady electric field on multipactor is also explored. Two effects related to dielectric material and metal are analyzed in detail. The SE emission from dielectric material is held back by the steady electric field and some low energy electrons return back to the dielectric materials. The effective SEY thus decreases. On the other hand, the electric field reduces the landing electron energy on the metal, and the corresponding SEY also decreases. The electron oscillation condition with considering both microwave field and stead electric field is derived and the threshold values for microwave power of multipactor are calculated. The susceptibility curves corresponding to different materials are plotted. Our result may be used to choose the filling dielectric materials for a microwave device.

Band-gap engineering of layered covalent organic frameworks via controllable exfoliation for enhanced visible-light-driven hydrogen evolution

Covalent organic frameworks (COFs) has become known as a promising organic photocatalyst for hydrogen evolution reaction (HER) because of its highly designable structure at the molecular level and other advantages related to the photocatalytic reaction. Here, we report a facile approach to prepare few-layer COFs nanosheets from a typical layered COF (covalent triazine frameworks, CTFs) via intercalation and exfoliation with H2SO4 and (NH4)2S2O8. Both the experiments and DFT calculations revealed the exfoliated CTFs nanosheets owned tunable optical and electronic properties because of the introduced defect states. It can not only narrow the bandgap for improved visible light absorption, but also suppress the radiative electron-hole recombination. Besides, the ultrathin structure can shorten the diffusion length of the photoexcited electrons and provide more active sites. As a result, the exfoliated nanosheets (especially the FL-CTF-2 with an apparent quantum yield of 11.14%) show much-improved performance in visible-light-driven HER compared with bulk CTFs. This work provides a new route to tail the photoelectric properties of COFs and may promote their applications in solar energy capture and conversion.

Tailoring the Photoelectrochemical Activity of TiO2 Electrodes by Multilayer Screen‐Printing

AbstractScreen‐printing is a commonly used method for the preparation of photoelectrodes. Although previous studies have explored the effect of the number of printed layers on the efficiency of dye‐sensitized solar cells, its interplay with the photoelectrocatalytic properties of the electrodes has rarely been examined. This study focuses on this issue by studying the photoelectrocatalytic oxidation of methanol over TiO2 electrodes. Incident photon‐to‐current efficiencies reached 87 % at the optimal conditions of monochromatic (338 nm) irradiation of one‐layer films at 0.2 V vs NHE. However, the irradiation wavelength and applied bias strongly influenced the relative behavior of the films. For instance, at 0.5 V and 327 nm irradiation, the one‐layer electrode was 6 times more efficient than the four‐layer one, while at 385 nm the four‐layer electrode was 3.5 times more efficient. The results were explained on the basis of differing light absorption properties and charge carrier lifetimes. Modelling and quantification of the electron diffusion length (5.7 μm) helped to explain why the two‐layer electrode (4.89 μm thick) showed the most consistent efficiencies across all conditions. Complementarily, transient absorption spectroscopy was used to correlate the thicknesses with charge carrier lifetimes. Electron transfer to FTO was apparent only for the thinner electrode. Our work shows that the optimization of photoelectrocatalytic processes should include the number of layers as a key variable.

Pseudocapacitive Charge Storage in Thin Nanobelts

This article reports that extremely thin nanobelts (thickness ~ 10 nm) exhibit pseudocapacitive (PC) charge storage in the asymmetric supercapacitor (ASC) configuration, while show battery-type charge storage in their single electrodes. Two types of nanobelts, viz. NiO–Co3O4 hybrid and spinal-type NiCo2O4, developed by electrospinning technique are used in this work. The charge storage behaviour of the nanobelts is benchmarked against their binary metal oxide nanowires, i.e., NiO and Co3O4, as well as a hybrid of similar chemistry, CuO–Co3O4. The nanobelts have thickness of ~ 10 nm and width ~ 200 nm, whereas the nanowires have diameter of ~ 100 nm. Clear differences in charge storage behaviours are observed in NiO–Co3O4 hybrid nanobelts based ASCs compared to those fabricated using the other materials—the former showed capacitive behaviour whereas the others revealed battery-type discharge behaviour. Origin of pseudocapacitance in nanobelts based ASCs is shown to arise from their nanobelts morphology with thickness less than typical electron diffusion lengths (~ 20 nm). Among all the five type of devices fabricated, the NiO–Co3O4 hybrid ASCs exhibited the highest specific energy, specific power and cycling stability.

Morphology control of organic halide perovskites by adding BiFeO3 nanostructures for efficient solar cell

The morphology of perovskite light-absorption layer plays an important role in the performance of perovskite solar cells (PSCs). In this work, BiFeO3 (BFO) nanostructures were used as additive for CH3NH3PbI3 (MAPbI3) via anti-solvent method. The addition of BFO nanostructures greatly enhanced the crystallinity, grain size and film uniformity of MAPbI3. As a result, the charge carrier mobility and electron diffusion length increased, leading to the increase of the short circuit current (JSC) of PSCs. This work provides a very simple but effective approach to improve the morphology of perovskite layer for efficient PSCs.

Photoelectrochemical evaluation of SILAR-deposited nanoporous BiVO4 photoanodes for solar-driven water splitting

We report a photoelectrochemical investigation of BiVO 4 photoanodes prepared by successive ionic layer adsorption and reaction (SILAR), a facile method that yields uniform nanoporous films. After characterization of the phase, morphology, composition, and optical properties of the prepared films, the efficiencies of charge separation ( η sep ) and water oxidation ( η ox ) in solar water splitting cells employing these photoanodes were estimated following a previously reported procedure. Unexpected wavelength and illumination direction dependencies were discovered in the derived efficiencies, casting doubt on the validity of the analysis. An alternative approach using a diffusion–reaction model that explicitly considers the efficiency of electron collection resolved the discrepancies and explained the illumination direction dependence of the photocurrent. Electron diffusion lengths ( L n ) of 0.45 μm and 0.55 μm were derived for pristine and cobalt phosphate (Co-Pi) modified BiVO 4 , respectively, which are much shorter than the film thickness of ~2.1 μm. The Co-Pi treatment also increased η ox from 0.86 to ~1, which is the main reason for the overall performance enhancement caused by adding Co-Pi. These findings suggest that there is little scope for improving the performance of SILAR-deposited BiVO 4 photoanodes by further catalyzing water oxidation, but enhanced performance is achievable if electron transport can be improved.

Enhancing electron diffusion length in narrow-bandgap perovskites for efficient monolithic perovskite tandem solar cells

Developing multijunction perovskite solar cells (PSCs) is an attractive route to boost PSC efficiencies to above the single-junction Shockley-Queisser limit. However, commonly used tin-based narrow-bandgap perovskites have shorter carrier diffusion lengths and lower absorption coefficient than lead-based perovskites, limiting the efficiency of perovskite-perovskite tandem solar cells. In this work, we discover that the charge collection efficiency in tin-based PSCs is limited by a short diffusion length of electrons. Adding 0.03 molar percent of cadmium ions into tin-perovskite precursors reduce the background free hole concentration and electron trap density, yielding a long electron diffusion length of 2.72 ± 0.15 µm. It increases the optimized thickness of narrow-bandgap perovskite films to 1000 nm, yielding exceptional stabilized efficiencies of 20.2 and 22.7% for single junction narrow-bandgap PSCs and monolithic perovskite-perovskite tandem cells, respectively. This work provides a promising method to enhance the optoelectronic properties of narrow-bandgap perovskites and unleash the potential of perovskite-perovskite tandem solar cells.

Facile RbBr interface modification improves perovskite solar cell efficiency

High-performance hybrid perovskite solar cell (PSC) is an emerging generation of energy material by virtue of its excellent properties such as wide light absorption range, large electron diffusion length, and small exciting energy. However, to date, methods of perovskite deposition generally do not offer desired film coverage, resulting in the direct interfacial contact, which seriously deteriorates the photovoltaic performance of devices. To improve the interfacial functions of the perovskite layer (PL)/electron transport layer (ETL) of the PSC devices, rubidium bromide (RbBr) is applied as a facile interfacial modifier. It is sandwiched between ETL tin oxide (SnO2) and PL [Cs0.05(MA0.17FA0.83)0.95Pb(I0·83Br0.17)3] to a fabricate a planar PSC. The RbBr modification of the PSC fluorine-doped tin oxide/SnO2/(RbBr)/PL/spiro-OMeTAD/Au (2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spiro-bifluorene) can reduce the energy barrier at the ETL/PL interface, improve the electronic contact between PL and ETL, and accelerate the electron extraction process. The RbBr modification thus leads to a higher power conversion efficiency of 18.29% for the PSC, as compared with 16.03% without RbBr modification. The facile RbBr modification procedure and significant performance advancement pave the way for future energy studies.

Insights into the Surface Science, Storage Mechanism and Electrochemical Phase Evolution of MoS2/CNT Hybrid Electrodes for Supercapacitive Application

Lately, layered MoS2 is found to be one of the most researched pseudocapacitive electrode material for Li+ and Na+ ion batteries because of its unique layered structure for initial ion intercalation and de‐intercalation and high conversion chemistry. As far as supercapacitors are considered, the charge storage in nanostructured MoS2 takes place via electric double layer formation, intercalation and de-intercalation pseudocapacitance and redox pseudocapacitance. Recently, a vast majority of studies on layered MoS2, have been focused on designing hierarchical deformed structures instead of regularly ordered crystallites which may accommodate intercalation stress upto some extent while retaining the original structure. In this study, we have synthesized large aspect ratio carbon nanotubes with a high specific surface area and an appropriate superstructure forming a thin layer of molybdenum disulfide nanoflakes hierarchically dispersed on the surface of the CNTs. This novel technique of preparing MoS2@CNT superstructure using a combination of chemical and physical deposition techniques proved to be very efficient in structurally engineering the microstructure of electrode material. Moreover, sputtering as a fabrication technique, provided an opportunity to precisely grow hierarchical structured MoS2 nanoflakes uniformly throughout the matrix, easily scalable and controllable at lengths down to nanometer ranges irrespective of superhydrophobic nature of CVD grown CNTs. The designed hybrid nanostructure form an open porous network with shorter ionic as well as electron diffusion lengths and provides larger number of intercalation sites. The super capacitive measurements of the MoS2@CNT electrode revealed capacity of 337 mF/cm2 at the sweep rate of 5 mV/s. The storage mechanism involves both electrostatic ionic adsorption as well as Na+ intercalation into the MoS2@CNT matrix. The electrochemical performance of the hybrid is far more superior due to the contribution from both faradaic and non-faradaic processes. Also, the cyclic retention have been immensely improved as compared to bare CNT and MoS2 and has shown a retention of 97.6% after 3500 cycles. Further, to elucidate the charge storage mechanism Trasatti’s and Dunn’s analysis are performed which suggest that pseudocapacitive phenomenon is dominantly responsible for superior charge storage in the hybrid. The electrodes subjected to 10, 50, 1000, 2000 and 3500 charging discharging cycles at 100mV/s were then analyzed using X-ray photoelectron spectrophotometer to understand the change in surface science of the material and reason behind cyclic fading. The phase transformation of electrode suggests that the binding energies of MoS2 shits towards shifts towards lower energies after cycling. This shift indicates partial transition of 2H→1T MoS2 phase due to the transverse gliding of S plane upon the intercalation of electrolytic ions. Additionally, we observed the formation of thin MoO3 oxide layer on the surface of electrode which may be due to the presence of dangling bonds generated by ionic intercalation. Thus, this thin insulating layer may be the reason of capacitive fading after 3500 cycles of constant charging and discharging. The all solid state supercapacitor built using symmetric MoS2@CNT electrodes was found to have high areal and volumetric capacitance of 131 mF/cm2 and 2.9 F/cm3 respectively, with high cyclic stability of 97.6% after 2500 cycles. Figure 1

Physical Properties and Theoretical Study of NixCo3-xO₄ (0 ≤ x ≤ 1.5) Nanostructures as High-Performance Electrode Materials for Supercapacitors.

Study evaluates the electrochemical performance of off-stoichiometric NixCo3-xO₄ compounds. The off-stoichiometric samples were prepared via hydrothermal technique by systematically varying Co/Ni molar ratio. Physical and electrochemical properties of NixCo3-xO₄ were observed to be stoichiometry dependent. The increase in Ni/Co ratio in NixCo3-xO₄ leads to the morphological transformation from fibrous bundles to urchin like nanospheres with a concomitant increase in the surface area reaching up to 132 m2/g. The optimal specific capacitance of 225 F/g at a current density of 1 A/g and 524 F/g at 10 mV/s scan rate was observed of x 1.0 sample, with an increased retention capacity ∼120% measured at 2 A/g current density. The hybrid density functional theory (DFT) calculations of the electronic density of states identified Ni1.0Co₂O₄ with optimal band-gap of 2.38 eV with an expectation of displaying higher electrocapacitive performance. Experimentally, Ni0.92Co2.08O₄ displayed superior electrocapacitive performance among all Ni/Co ratio in NixCo3-xO₄. The DFT study also predicted Ni preference to the octahedral site, which is in-line with the observed increase in ferromagnetic nature, decreased lattice parameter, and increased structural disorder with increasing Ni/Co ratio. The improved electrochemical performance of NixCo3-xO₄ (x > 0) is attributed to the mesoporous hierarchical structure, with a high electroactive surface which can effectively improve structural stability, and reduce the ionic and electron diffusion length. Compared to the pure Co₃O₄, the reduction of Co content in NixCo3-xO₄ is desired due to the high cost and toxicity of Co element.

Mid-Wave Infrared InAs/GaSb Type-II Superlattice Photodetector With n-B-p Design Grown on GaAs Substrate

In this paper, we report the direct growth and characterization of a mid-wave infrared InAs/GaSb type-II superlattice n-B-p photodetector on a GaAs substrate. The design consists of an n-doped contact, a wide bandgap unipolar barrier, and a p-doped absorber, which uses photogenerated electron as minority carriers to enjoy the longer electron diffusion length compared with hole diffusion length. At 77 K, the device exhibits a dark current density of $2.9\times 10^{-5}$ A/cm2 under −0.1 V and a zero-bias differential-resistance-area product (R0A) in excess of $8\times 10^{3}~ \Omega \cdot \text {cm}^{2}$ . Arrhenius analysis of dark current demonstrates that the dominant mechanism is diffusion at a temperature higher than 130 K. 50% cutoff wavelength of the detector is found at $6.4~\mu \text{m}$ at 77 K under zero bias, with a peak responsivity of 0.56 A/W. The corresponding specific detectivity is $7.6\times 10^{11}~\text {cm}\cdot \text {Hz}^{1/2}$ /W. The key device parameters which limit the further optimization of performance are discussed.

Few-Layer to Multilayer Germanium(II) Sulfide: Synthesis, Structure, Stability, and Optoelectronics.

Among 2D/layered semiconductors, group IV monochalcogenides such as SnS(e) and GeS(e) have attracted attention as phosphorene/black phosphorus analogues with anisotropic structures and predicted unusual properties. In contrast to SnS, for which bottom-up synthesis has been reported, few-layer GeS has been realized primarily via exfoliation from bulk crystals. Here, we report the synthesis of large (up to >20 μm), faceted single crystalline GeS flakes with anisotropic properties using a vapor transport process. In situ electron microscopy is used to identify the thermal stability and sublimation pathways, and demonstrates that the GeS flakes are self-encapsulated in a thin, sulfur-rich amorphous GeSx shell during growth. The shell provides exceptional chemical stability to the layered GeS core. In contrast to exfoliated GeS, which rapidly degrades during exposure to air, the synthesized GeS-GeSx core-shell structures show no signs of chemical attack and remain unchanged in air for extended time periods. Measurements of the optoelectronic properties by photoluminescence spectroscopy show a tunable bandgap due to out-of-plane quantum confinement in flakes with thickness below 100 nm. Cathodoluminescence (CL) spectroscopy with nanoscale excitation provides evidence for interfacial charge transfer due to a type II heterojunction between the crystalline core and amorphous shell. Measurements by locally excited CL yield a minority carrier (electron) diffusion length in the p-type GeS core = 0.27 μm, on par with diffusion lengths in the highest-quality layered chalcogenide semiconductors.

Pre- or post-TiCl4 treated TiO2 nano-array photoanode for QDSSC: Ti3+ self-doping, flat-band level and electron diffusion length

Of the photoanode in QDSSC, the TiCl4 solution treatment is widely used in mesoporous TiO2 surface modification. However, device performance amplification and electron transfer capability improvement of the two common pre- or post treatment are seldom yet. In this work, we explore the TiCl4 different treatments based on the typical TiO2 nanowire array photoanode for CdSxSe1-x QDSSC. In terms of the changes of electron transfer pathway, flat-band potential (Vfb) and charge carrier concentration (ND), we explored the inducement and increase of electron transfer capability and efficacy under different treatments. As for the influence of device performance, the more negative Vfb (−0.315 V, NHE) and higher ND (7.63 × 1019 cm−3) of PBS are beneficial to the increase of open-circuit voltage (Voc) and short-circuit current (Jsc). Therefore, the TiCl4 pre-treatment on photoanode modification (in PBS) is beneficial to reduce the resistances of charge transfer and recombination. The cell performance of PBS in CdSxSe1-x QD sensitization was improved significantly: the PCE was 7.54%, the Jsc was 18.93 mA/cm2, Voc was 0.78 V and fill factor (FF) was 51.1%.

Ultrathin 2D/2D ZnIn2S4/MoS2 hybrids for boosted photocatalytic hydrogen evolution under visible light

A well-connected hetero-layered ZnIn2S4/MoS2 composite was fabricated via an electrostatic self-assembly process to boost photocatalytic hydrogen evolution under visible-light irradiation. Ultrathin nanosheets contribute to efficient charge transfer by reducing electron diffusion length. In the sheet-on-sheet heterostructure, ultrathin ZnIn2S4 nanosheets (NSs) and MoS2 NSs were well connected with each other to form a large and intimate contact interface, which features an efficient separation and migration of photoinduced charge carriers. Moreover, MoS2 NSs endow the composite with abundant active sites and lowers its overpotential for water reduction. Consequently, the ultrathin hetero-layered ZnIn2S4/MoS2 composite with optimized loading of MoS2 achieves a hydrogen production rate of 4.974 mmol g−1 h−1, which is ca. 50 times as much as that of pure ZnIn2S4, and 2.2 times as much as that of its ZnIn2S4/Pt counterpart. This work provides inspiration for the fabrication of well-contacted hetero-layered structure for photocatalytic hydrogen evolution.

Colloidal synthesis of Y-doped SnO2 nanocrystals for efficient and slight hysteresis planar perovskite solar cells

It is well known that the electron-transporting layers (ETLs) play an indispensable role in any types of high efficient perovskite solar cells (PSCs) because of their important functions in extracting/transporting electrons and blocking holes during the light-to-electricity conversion process. High quality ETLs are necessary for preparing efficient planar PSCs because the electron diffusion length is shorter than its hole counterpart in perovskite materials and the planar PSCs have short electrons extracting channels due to the lack of mesoporous layers. Recently, impressive advances in planar PSCs with SnO2 ETLs have been reported due to the perfect characteristics of SnO2 material including suitable energy level, high electron mobility, good transmittance, excellent chemical stability, inactive UV photocatalysis, and so on. Here, we use the doping route to further enhance the quality of SnO2 ETLs. The SnO2 nanocrystals are doped with Y3+ through the typical solvothermal method. The Y dopant leads to more suitable energy level structure and better charge carrier dynamics in the devices than those of the undoped ones. The planar PSCs with Y-SnO2 ETLs achieve a champion efficiency of 20.71% with slight hysteresis, much higher than the undoped ones (18.08%).