One-step hydrothermal synthesis of S-defect-controlled ZnIn_(2)S_(4) microflowers with improved kinetics process of charge-carriers for photocatalytic H_(2) evolution

Engineering lattice defects in two-dimensional(2 D) sulfide semiconductors has been accepted as an effective strategy to enhance the efficiency of the solar-to-fuels conversion.Although many researches have proven the lattice defect-mediated photocatalytic activity of ZnIn_(2)S_(4),the artificial control of Sdefects for optimizing the charge-carrier kinetics process in ZnIn_(2)S_(4) has long been a challenging task.Herein,we report a facile one-step method to modulate the lattice S-content of ZnIn_(2)S_(4) microflowers(MFs) only through adjusting the used amount of S-precursor in the hydrothermal solution that contains the metal precursors with a fixed Zn/In stoichiometric ratio at 1:2.We also demonstrated that the Svacancies at the In facets were the main type of lattice defects in the formed ZnIn_(2)S_(4) MFs,which could enhance both the separation and migration processes of the photoinduced charge-carriers due to the existence of discrete defect energy-levels(DELs) and the reduced effective mass of electrons,as evidenced by the first-principles calculations and the electron spectra analyses.The ZnIn_(2)S_(4) MFs with the optimal content of S-vacancy obtained by a hydrothermal treatment of the precursors with the Zn/In/S stoichiometric ratio of 1:2:8 possessed the long-lived photoinduced electron(~94.64 ns) for contributing to the photo-physical and-chemical processes.Thus,upon visible light irradiation,the H_(2)-evolution rate of this sample reached ~2.40 mmol h^(-1) g^(-1) with an apparent quantum efficiency of ~0.16% at 420 nm even though only using 5 mg of photocatalysts without any cocatalysts.

Energy band and charge-carrier engineering in skutterudite thermoelectric materials

The binary CoSb_(3) skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of CoSb_(3) materials can be significantly reduced through phonon engineering, such as low-dimensional structure, the introduction of nano second phases,nanointerfaces or nanopores, which greatly improves their ZT values. The phonon engineering can optimize significantly the thermal transport properties of CoSb_(3)-based materials. However, the improvement of the electronic transport properties is not obvious, or even worse. Energy band and charge-carrier engineering can significantly improve the electronic transport properties of CoSb_(3)-based materials while optimizing the thermal transport properties. Therefore, the decoupling of thermal and electronic transport properties of CoSb_(3)-based materials can be realized by energy band and charge-carrier engineering. This review summarizes some methods of optimizing synergistically the electronic and thermal transport properties of CoSb_(3) materials through the energy band and charge-carrier engineering strategies. Energy band engineering strategies include band convergence or resonant energy levels caused by doping/filling. The charge-carrier engineering strategy includes the optimization of carrier concentration and mobility caused by doping/filling, forming modulation doped structures or introducing nano second phase. These strategies are effective means to improve performance of thermoelectric materials and provide new research ideas of development of high-efficiency thermoelectric materials.

Recent development in metal halide perovskites synthesis to improve their charge-carrier mobility and photocatalytic efficiency

Over the past decade,all-inorganic metal halide perovskites(MHPs,CsPbX_(3):X=Cl,Br,I)have been widely investigated as promising materials for optoelectronic devices such as solar cells and light-emitting diodes.MHPs are defecttolerant,which allows tuning of their bandgap without altering their photophysical properties.From a fundamental point of view,MHPs are excellent candidates for photocatalytic reactions due to their light-harvesting capability,high photogenerated charge-carrier mobility,long diffusion lengths,and tunable bandgap energy.In this review,we provide an overview of various MHP engineering strategies(e.g.,surface,morphological,and structural modifications,heterojunction coupling,and encapsulation)which are directly linked to the charge-carrier mobility and lifetimes,and then to the photocatalytic efficiency.Specifically,we outline different synthetic approaches resulting in surface and morphological modifications,anion/cation substitution,metallic doping,coupling,and encapsulation that tremendously influence MHPs’stability,optical properties,and charge-carrier dynamics at variable time scales(from fs toμs).We also provide an in-depth evaluation of the MHPs for variable photoredox reactions,discussing how the optical and electronic properties help to improve their stability and efficiency.

Charge-carrier photogeneration and extraction dynamics of polymer solar cells probed by a transient photocurrent nearby the regime of the space charge-limited current

To understand the complex behaviors of photogenerated charge carriers within polymer-based bulk-heterojunction-type solar cells,the charge-carrier photogeneration and extraction dynamics are simultaneously estimated using a transient photocurrent technique under various external-bias voltages,and a wide range of excitation intensities are analyzed.For this purpose,conventional devices with 80 nm thick active layers consisting of a blend of representative P3HT and PTB7 electron-donating polymers and proper electron-accepting fullerene derivatives were used.After the correction for the saturation behavior at a high excitation-intensity range nearby the regime of the space charge-limited current,the incident-photon-density-dependent maximum photocurrent densities at the initial peaks are discussed as the proportional measures of the charge-carrier-photogeneration facility.By comparing the total number of the extracted charge carriers to the total number of the incident photons and the number of the initially photogenerated charge carriers,the external quantum efficiencies as well as the extraction quantum efficiencies of the charge-carrier collection during a laser-pulse-induced transient photocurrent process were obtained.Subsequently,the charge-carrier concentration-dependent mobility values were obtained,and they are discussed in consideration of the additional influences of the charge-carrier losses from the device during the charge-carrier extraction that also affects the photocurrent-trace shape.

In-depth understanding the effect of electron-withdrawing/-donating groups on the interfacial carrier dynamics in naphthalimide-treated perovskite solar cells

Surface defect passivation of perovskite films through chemical interaction between specific functional groups and defects has been proven to be an effective technique for enhancing the performance and stability of perovskite solar cells(PSCs).However,an in-depth understanding of how these passivation materials affect the intrinsic nature of charge-carrier transfer kinetics in PSCs remains shielded so far.Herein,we have designed two naphthalimide-based perovskite surface passivators having electronwithdrawing(-CF_(3),NSF)or electron-donating(-CH_(3),NSC)substituents for use in PSCs.Transient absorption spectroscopy(TA)measurements confirmed how the electron-withdrawing and electron-donating groups can efficiently turn the hot carriers(HCs)cooling and injection,and interface recombination in the device.We found that NSC-passivated perovskite samples exhibit faster hot-carriers(HCs)injection from the perovskite layer into carrier transport layers before cooling to the crystal lattice compared with the NSF-based and control ones with the order:NSC>NSF>control.Fast HCs injection is advantageous to minimize the charge-carriers recombination and improve PSCs performance.The carrier lifetime in NSCtreated device measured by nanosecond TA exhibits nearly~2 times longer than that of NSF-based device,which demonstrates the decreased charge-carrier recombination in NSC-treated device.As expected,the power conversion efficiency(PCE)of the NSC-treated PSCs is improved to 23.04%compared with that of the device treated with NSF(21.81%).Our findings provide invaluable guide for developing highly efficient passivators to further boost PSCs photovoltaic performance.

Boosting efficiency and stability of 2D alternating cation perovskite solar cells via rational surface-modification: Marked passivation efficacy of anion

Two-dimensional(2D) alternating cation(ACI) perovskite surface defects,especially dominant iodine vacancies(V_Ⅰ) and undercoordinated Pb^(2+),limit the performance of perovskite solar cells(PVSCs).To address the issue,1-butyl-3-methylimidazolium trifluoro-methane-sulfonate(BMIMOTF) and its iodide counterpart(BMIMI) are utilized to modify the perovskite surface respectively.We find that BMIMI can change the perovskite surface,whereas BMIMOTF shows a nondestructive and more effective defect passivation,giving significantly reduced defect density and suppressed charge-carrier nonradiative recombination.This mainly attributes to the marked passivation efficacy of OTF-anion on V_Ⅰ and undercoordinated Pb^(2+),rather than BMIMI^(+) cation.Benefiting from the rational surface-modification of BMMIMOTF,the films exhibit an optimized energy level alignment,enhanced hydrophobicity and suppressed ion migration.Consequently,the BMIMOTF-modified devices achieve an impressive efficiency of 21.38% with a record open-circuit voltage of 1.195 V,which is among the best efficiencies reported for 2D PVSCs,and display greatly enhanced humidity and thermal stability.

Using the Hg_xMg_(1-x)Te ternary compound as a room temperature photodetector: The electronic structure, charge transport, and response function of the energetic electromagnetic radiation

In the present work, firstly, a first-principles study of the structural, electronic, and electron transport properties of the HgxMg1-xTe（HMT） ternary compound is performed using the ABINIT package and the results are compared with Cd0.9Zn0.1 Te（CZT） as a current room-temperature photodetector. Next, the response functions of Hg0.6Mg0.4Te and Cd0.9Zn0.1Te under electromagnetic irradiation with 0.05 Me V, 0.2 MeV, 0.661 MeV and 1.33 MeV energies are simulated by using the MCNP code. According to these simulations, the Hg0.6Mg0.4Te ternary compound is suggested as a good semiconductor photodetector for use at room temperature.

Constructing the separation pathway for photo-generated carriers by diatomic sites decorated on MIL-53-NH2(Al)for enhanced photocatalytic performance

High yield production of phenol from hydroxylation of benzene with low energy consumption is of paramount importance,but still challenging.Herein,a new strategy,consisting of using diatomic synergistic modulation(DSM)to effectively control the separation of photo-generated carriers for an enhanced production of phenol is reported.The atomic level dispersion of Fe and Cr respectively decorated on Al based MIL-53-NH_(2)photocatalyst(Fe1/Cr:MIL-53-NH_(2))is designed,in which Cr single atoms are substituted for Al3+while Fe single atoms are coordinated by N.Notably,the Fe1/Cr:MIL-53-NH_(2)significantly boosts the photooxidation of benzene to phenol under visible light irradiation,which is much higher than those of MIL-53-NH_(2),Cr:MIL-53-NH_(2),Fe1/MIL-53-NH_(2),and Fe nanoparticles/Cr:MIL-53-NH_(2)catalysts.Theoretical and experimental results reveal that the Cr single atoms and Fe single atoms can act as electron acceptor and electron donor,respectively,during photocatalytic reaction,exhibiting a synergistic effect on the separation of the photo-generated carriers and thereby causing great enhancement on the benzene oxidation.This strategy provides new insights for rational design of advanced photocatalysts at the atomic level.

The role of phase impurities and lattice defects on the electron dynamics and photochemistry of CuFeO2 solar photocathodes

CuFeO2 is a promising photocathode for H2 evolution and CO2 reduction reactions.To better understand the complex defect chemistry and role of impurity phases in this material and their effect on the photochemical performance,we employ visible light transient absorption spectroscopy and density functional theory(DFT)calculations to investigate the electron dynamics in electrochemically deposited Cu-Fe oxide thin films.Kinetic analysis of carrier lifetime shows a fast,sub-ps contribution to relaxation followed by persistence of a Iong-lived state to time delays greater than 2 ns.Increasing amplitude of the Iong-lived state is shown to correlate with the rate of fast initial relaxation,and this is explained in terms of a competition between charge carrier trapping and charge separation.Charge separation in CuFeO2 occurs via hole thermalizati on from O 2p to Cu 3d vale nee band states leadi ng to segregatio n of electr ons and holes across layers in the CuFeO2 lattice.Correlation between transient absorption measurements and DFT calculations suggest that Cu vacancies enhanee photochemical performance by facilitating charge separation kinetics.In contrast,O interstitials are predicted to switch the relative positions of O 2p and Cu 3d vale nee band states,which would in hibit charge separatio n by in ter-band hole thermal izatio n.Fin ally,we find no evide nee for electron in jecti on from CuFeO2 to CuO suggest!ng that charge separati on at this heterostructure in terface does not play a role in the carrier lifetime or photochemical performance of the catalysts studied here.

Stable and high performance all-inorganic perovskite light-emitting diodes with anti-solvent treatment

Optoelectronic applications based on the perovskites always face challenges due to the inherent chemical composition volatility of perovskite precursors. The efficiency of perovskite-based light-emitting diodes(Pe-LEDs) can be enhanced by improving the perovskite film via solvent engineering. A dual solvent post-treatment strategy was applied to the perovskite film, which provides a synchronous effect of passivating surface imperfections and reduces exciton quenching, as evidenced by improved surface morphology and photoluminance. Thus, the optimized Pe-LEDs reach 17,866 cd · m-2 maximum brightness, 45.8 cd · A-1 current efficiency, 8.3% external quantum efficiency, and relatively low turn-on voltage of2.0 V. Herein, we present a simple technique for the fabrication of stable and efficient Pe-LEDs.

Reducing Packing Factor of Znln2S4 to Promote Photocatalytic Activity

Due to the quite sluggish charge-carrier separation in semiconductor photocatalysts,the photocatalytic ac-tivity of these materials is still far inferior than anticipated.Herein,a novel approach to reducing the packing factor(PF)of Znln2S4 semiconductors to improve the charge-carrier separation is offered.The well-crystallized Zn1-xIn2S4-x(x=0,0.05,0.1)powders were productively prepared through solid-state reactions.Their structures were verified by the high-resolution transmission electron microscopy,powder X-ray diffraction,and X-ray photoelectron spectroscopy.The PE values of Zn1-xIn2S4-x(x=0,0.05,0.1)samples were calculated to be 0.683.0.651.and 0.618.respectively.The reduction.of the PF for Zn1-xIn2S4-x with increasing x can promote the separation of photoexcited carriers,and this process was endorsed by their photoelectric response and photoluminescence emission spectra.The Zn0.9In2S3.9 sample with a lower PF value presents roughly 21 times higher photocurrent density and four times higher photodegrading rate of methyl orange than those of pristine ZnIn2S4.

Strategies for high-performance perovskite solar cells from materials, film engineering to carrier dynamics and photon management

In recent years,halide perovskite solar cells(HPSCs)have attracted a great atten-tion due to their superior photoelectric performance and the low-cost of processing their quality films.In order to commercialize HPSCs,the researchers are focusing on developing high-performance HPSCs.Many strategies have been reported to increase the power conversion efficiency and the long-term stability of HPSCs over the past decade.Herein,we review the latest efforts and the chemical-physical principles for preparing high-efficiency and long-term stability HPSCs in particu-lar,concentrating on the perovskite materials,technologies for perovskite films,charge transport materials and ferroelectric effect to reduce the carrier loss,and photon management via plasmonic and upconversion effects.Finally,the key issues for future researches of HPSCs are also discussed with regard to the require-ments in practical application.