Quantitative measurement of the charge carrier concentration using dielectric force microscopy

The charge carrier concentration profile is a critical factor that determines semiconducting material properties and device performance.Dielectric force microscopy(DFM)has been previously developed to map charge carrier concentrations with nanometer-scale spatial resolution.However,it is challenging to quantitatively obtain the charge carrier concentration,since the dielectric force is also affected by the mobility.Here,we quantitative measured the charge carrier concentration at the saturation mobility regime via the rectification effect-dependent gating ratio of DFM.By measuring a series of n-type GaAs and GaN thin films with mobility in the saturation regime,we confirmed the decreased DFM-measured gating ratio with increasing electron concentration.Combined with numerical simulation to calibrate the tip–sample geometry-induced systematic error,the quantitative correlation between the DFM-measured gating ratio and the electron concentration has been established,where the extracted electron concentration presents high accuracy in the range of 4×10^(16)–1×10^(18)cm^(-3).We expect the quantitative DFM to find broad applications in characterizing the charge carrier transport properties of various semiconducting materials and devices.

Two-Dimensional Transition Metal Dichalcogenides and Their Charge Carrier Mobilities in Field-Effect Transistors

Two-dimensional(2D) materials have attracted extensive interest due to their excellent electrical, thermal,mechanical, and optical properties. Graphene has been one of the most explored 2D materials. However, its zero band gap has limited its applications in electronic devices. Transition metal dichalcogenide(TMDC), another kind of 2D material,has a nonzero direct band gap(same charge carrier momentum in valence and conduction band) at monolayer state,promising for the efficient switching devices(e.g., field-effect transistors). This review mainly focuses on the recent advances in charge carrier mobility and the challenges to achieve high mobility in the electronic devices based on 2DTMDC materials and also includes an introduction of 2D materials along with the synthesis techniques. Finally, this review describes the possible methodology and future prospective to enhance the charge carrier mobility for electronic devices.

Modulating charge carriers in carbon dots toward efficient solar-to-energy conversion

Growing attention to the development of sustainable solar-to-energy conversion applications has resulted in the synthesis of promising and environment-friendly nanomaterials as energy harvesters.Among various carbon nanomaterials,carbon dots(CDs)have received significant attention due to their excellent light absorption capability,broad absorption region,and superior photostability with enormous potential for solar energy applications.Therefore,utilizing and modulating the charge carriers generated from CDs is critical for achieving a high energy conversion efficiency of CDs.Herein,we focus on the distinct characteristics of CDs as energy converters from charge excitation to charge separation and transfer for various solar-to-energy applications,including photovoltaic cells,photocatalysts,and photoelectrocatalysts.We anticipate that this review will offer insight into the synthesis and design of novel nanocomposites with a fundamental analysis of the photochemical properties and future development of energy conversion devices.

A review of halide charge carriers for rocking-chair and dual-ion batteries

This review discusses how halide ion species have been used as charge carriers in both anion rocking-chair and dual-ion battery(DIB)systems.The anion rocking-chair batteries based on fluoride and chloride have emerged over the past decade and are garnering increased research interest due to their large theoretical energy density values and the natural abundance of halide-containing materials.Moreover,DIBs that use halide species as their anionic charge carrier are seen as one of the promising next-generation battery technologies due to their low cost and high working potentials.Although numerous polyatomic anions have been studied as charge carriers,the use of single halide ions(i.e.,F−and Cl−)and metal-based superhalides(e.g.,[MgCl_(3)]−)as anionic charge carriers in DIBs has been considerably less explored.Herein,we provide an overview of some of the key advances and recent progress that has been made with regard to halide ion charge carriers in electrochemical energy storage.We offer our perspectives on the current state of the field and provide a roadmap in hopes that it helps researchers toward making new advances in these promising and emerging areas.

First-principles hybrid functional study of the electronic structure and charge carrier mobility in perovskite CH_3NH_3SnI_3

We calculate the electronic properties and carrier mobility of perovskite CH3NH3SnI3as a solar cell absorber by using the hybrid functional method. The calculated result shows that the electron and hole mobilities have anisotropies with a large magnitude of 1.4 × 104cm2·V-1·s-1along the y direction. In view of the huge difference between hole and electron mobilities, the perovskite CH3NH3 Sn I3can be considered as a p-type semiconductor. We also discover a relationship between the effective mass anisotropy and electronic occupation anisotropy. The above results can provide reliable guidance for its experimental applications in electronics and optoelectronics.

Pressure-Induced Charge-Order Melting and Reentrant Charge Carrier Localization in the Mixed-Valent Pb3Rh7O15

The mixed-valent Pb3Rh7O15 undergoes a Verwey-type transition at Tv≈180K, below which the development of Rh3＋3＋/Rh4＋4＋ charge order induces an abrupt conductor-to-insulator transition in resistivity. Here we investigate the effect of pressure on the Verwey-type transition of Pb3Rh7O15 by measuring its electrical resistivity under hydrostatic pressures up to 8GPa with a cubic anvil cell apparatus. We find that the application of high pressure can suppress the Verwey-type transition around 3GPa, above which a metallic state is realized at temperatures below ～70K, suggesting the melting of charge order by pressure. Interestingly, the low-temperature metallic region shrinks gradually upon further increasing pressure and disappears completely at P〉7GPa, which indicates that the charge carriers in Pb3Rh7O15 undergo a reentrant localization under higher pressures. We have constructed a temperature-pressure phase diagram for Pb3Rh7O15 and compared to that of Fe3O4, showing an archetype Verwey transition.

Charge carrier dynamics in different crystal phases of CH_(3)NH_(3)PbI_(3)perovskite

Despite that organic-inorganic lead halide perovskites have attracted enormous scientific attention for energy conversion applications over the recent years,the influence of temperature and the type of the employed hole transport layer(HTL)on the charge carrier dynamics and recombination processes in perovskite photovoltaic devices is still largely unexplored.In particular,significant knowledge is missing on how these crucial parameters for radiative and non-radiative recombinations,as well as for efficient charge extraction vary among different perovskite crystalline phases that are induced by temperature variation.Herein,we perform micro photoluminescence(pPL)and ultrafast time resolved transient absorption spectroscopy(TAS)in Glass/Perovskite and two dierent Glass/ITO/HTL/Perovskite configurations at temperatures below room temperature,in order to probe the charge carrier dynamics of different perovskite crystalline phases,while considering also the effect of the employed HTL polymer.Namely,CH_(3)NH_(3)Pbb films were deposited on Glass,PEDOT:PSS and PTAA polymers,and the developed Glass/CH_(3)NH_(3)PbI_(3)and Glass/ITO/HTL/CH_(3)NH_(3)PbI_(3)architectures were studied from 85 K up to 215 K in order to explore the charge extraction dynamics of the CH_(3)NH_(3)PbI_(3)orthorhombic and tetragonal crystalline phases.It is observed an unusual blueshift of the bandgap with temperature and the dual emission at temperature below of 100 K and also,that the charge carrier dynamics,as expressed by hole injection times and free carrier recombination rates,are strongly depended on the actual pervoskite crystal phase,as well as,from the selected hole transport material.

Effect of Residual Charge Carrier on the Performance of a Graphene Field Effect Transistor

The temperature-dependent effect of residual charge carrier （no）, at the Dirac point, on mobility is studied. We fabricate and characterize a graphene field effect transistor （GFET） using 7nm TiO2 as the top-gate dielectric. The temperature-dependent gate voltage-drain current and room temperature gate capacitance are measured to extract the carrier mobility and to estimate the quantum capacitance of the GFET. The device shows the mobility value of gOO cm^2 /V.s at room temperature and it decreases to 45 cm^2 /V.s for 20 K due to the increase of n0. These results indicate that the phonon scattering is not the dominant process for the unevenness dielectric layer while the coulomb scattering by charged impurities degrades the device characteristically at low temperature.

Tuning the type of charge carriers in N-heterocyclic carbene-based molecular junctions through electrodes

Designing tunable molecular devices with different charge carriers in single-molecule junctions is crucial to the nextgeneration electronic technology.Recently,it has been demonstrated that the type of charge carriers depends on and can be tuned by controlling the molecular length and the number of interfacial covalent bonds.In this study,we show that the type of charge carriers can also be tuned by controlling the material and shape of electrodes.N-heterocyclic carbenes(NHCs)have attracted attention because of their ability to form strong,substitutional inert bonds in a variety of metals.Also,NHCs are more stable than the widely used thiol group.Therefore,we use electrodes to tune the type of charge carriers in a series of NHCs with different side groups.The ab initio calculations based on non-equilibrium Green’s formalism combined with density functional theory show that the dominant charge carrier switches from electrons to holes when gold electrodes are changed into platinum ones.The nature of the charge carriers can be identified by variations in the transport spectra at the Fermi level(EF),which are caused by the side groups.The projections of transport spectra onto the central molecules further validate our inferences.In addition,the transmission coefficient at EF is found to be dependent on the atomic interface structure.In particular,for the NHC without methyl or ethyl side groups,connecting a protruding atom on the electrode surface significantly enhances the transportability of both electrode materials.Overall,this study presents an effective approach to modifying transport properties,which has potential applications in designing functional molecular devices based on NHCs.

Pressure Effects on the Charge Carrier Transportation of BaF_2 Nanocrystals

The charge transport behavior of barium fluoride nanocrystals is investigated by in situ impedance measurement up to 35 GPa. It is found that the parameters change discontinuously at about 6.9 GPa, corresponding to the phase transition of BaF2 nanocrystals under high pressure. The charge carriers in BaF2 nanocrystals include both Fions and electrons. Pressure makes the electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge-discharge processes in the Fm3m phase more difficult.

Highly selective and efficient photocatalytic NO removal:Charge carrier kinetics and interface molecular process

The widespread nitrogen oxides(NOx,mainly in NO)in the atmosphere have threatened human health and ecological environment.The dilute NO(ppb)is difficult to efficiently remove via the traditional process due to its characteristics of low concentration,wide range,large total amount,etc.Photocatalysis can utilize solar energy to purify NO pollutants under mild conditions,but its application is limited due to the low selectivity of nitrate and poor activity of NO removal.The underlying reason is that the interface mechanism of NO oxidation is not clearly understood,which leads to the inability to accurately regulate the NO oxidation process.Herein,the recent advances in the photocatalytic oxidation of NO are summarized.Firstly,the common strategies to effectively regulate carrier dynamics such as morphology control,facet engineering,defect engineering,plasma coupling,heterojunction and single-atom catalysts are discussed.Secondly,the progress of enhancing the adsorption and activation of reactants such as NO and O_(2) during NO oxidation is described in detail,and the corresponding NO oxidation mechanisms are enumerated.Finally,the challenges and prospects of photocatalytic NO oxidation are presented in term of nanotechnology for air pollution control.This review can shed light on the interface mechanism of NO oxidation and provide illuminating information on designing novel catalysts for efficient NOx control.

Thiazoloisoindigo-based Polymer Semiconductors: Synthesis,Structure-Property Relationship, Charge Carrier Polarity, and Field-Effect Transistor Performance

Developing new polymeric semiconductors with excellent device performance is essential for organic electronics. Herein, we synthesized two new thiazoloisoindigo(Tz II)-based polymers, namely, P(Tz II-d Th-d Th) and P(Tz II-d Th-d Tz), by copolymerizing thiophene-flanked Tz II with bithiophene and bithiazole, respectively. Owing to the more electron-deficient nature of bithiazole than bithiophene, P(Tz II-d Th-d Tz)possesses deeper LUMO/HOMO levels of-3.45/-5.47 e V than P(Tz II-d Th-d Th)(-3.34/-5.32 e V). The organic field-effect transistor(OFET) devices based on P(Tz II-d Th-d Th) exhibited p-type behaviors with an average hole mobility value as high as 1.43 cm^(2)·V^(-1)·s^(-1), while P(Tz II-d Th-d Tz)showed typical ambipolar characteristics with average hole and electron mobilities of 0.38 and 0.56 cm^(2)·V^(-1)·s^(-1). In addition, we compared the performances of both polymers with other Tz II-based polymers reported in our previous work, and showed that the charge carrier polarity can be manipulated by adjusting the number of the thiophene units between the acceptor unit. As the increase of the number of thiophene rings,charge carrier polarity shifts from electron-dominated ambipolar transport to hole-dominated ambipolar transport and then to unipolar hole transport in OFETs, which provides an effective molecular design strategy for further optimization of polymer OFET performance.

Amplitude-mode spectroscopy of chemically injected and photogenerated charge carriers in semiconducting single-walled carbon nanotubes

In one-dimensional semiconductors such as conjugated polymers and semiconducting single-walled carbon nanotubes(s-SWCNTs),injected charge carriers(electrons or holes)can have profound impacts on both electronic conductivity and optical spectra,even at low carrier densities.Understanding charge-related spectral features is a key fundamental challenge with important technological implications.Here,we employ a systematic suite of experimental and theoretical tools to understand the mid-infrared charge signatures of heavily p-type doped polymer-wrapped s-SWCNTs.Across a broad range of nanotube diameters,we find that hole charge carriers induce strong Fano anti-resonances in mid-infrared transmission spectra that correspond to defect-related(D-band)and in-plane tangential(G-band)Raman-active vibrational modes,along with antiresonances arising from infrared(IR)-active polymer and SWCNT modes.We employ^(13)C isotope-labeled s-SWCNTs and a removable wrapping polymer to clarify the relative intensities,energies,and sources of all observed anti-resonances.Simulations performed with the“amplitude mode model”are used to quantitatively reproduce Raman spectra and also help to explain the outsized intensity of the D-band anti-resonance,relative to the G-band,observed for both moderately and degenerately doped s-SWCNTs.The results provide a framework for future studies of ground-and excited-state charge carriers in s-SWCNTs and a variety of low-dimensional materials.

Lateral quantum confinement regulates charge carrier transfer and biexciton interaction in CdSe/CdSeS core/crown nanoplatelets

Charge carrier dynamics essentially determines the performance of various optoelectronic applications of colloidal semiconductor nanocrystals.Among them,two-dimensional nanoplatelets provide new adjustment freedom for their unique core/crown heterostructures.Herein,we demonstrate that by fine-tuning the core size and the lateral quantum confinement,the charge carrier transfer rate from the crown to the core can be varied by one order of magnitude in CdSe/CdSeS core/alloy-crown nanoplatelets.In addition,the transfer can be affected by a carrier blocking mechanism,i.e.,the filled carriers hinder further possible transfer.Furthermore,we found that the biexciton interaction is oppositely affected by quantum confinement and electron delocalization,resulting in a non-monotonic variation of the biexciton binding energy with the emission wavelength.This work provides new observations and insights into the charge carrier transfer dynamics and exciton interactions in colloidal nanoplatelets and will promote their further applications in lasing,display,sensing,etc.

Metavalent bonding impacts charge carrier transport across grain boundaries

Understanding the mechanisms underpinning the charge carrier scattering at grain boundaries is crucial to design thermoelectrics and other electronic materials.Yet,this is a very challenging task due to the complex characteristics of grain boundaries and the resulting difficulties in correlating grain boundary structures to local properties.Recent advances in characterizing charge transport across grain boundaries are reviewed,demonstrating how the microstructure,composition,chemical bonding and electrical properties of the same individual grain boundary can be correlated.A much higher potential barrier height is observed in high-angle grain boundaries.This can be ascribed to the larger number density of deep trapping states caused by the local collapse of metavalent bonding.A novel approach to study the influence of the local chemical bonding mechanism around defects on the resulting local properties is thus developed.The results provide insights into the tailoring of electronic properties of metavalently bonded compounds by engineering the characteristics of grain boundaries.

Advanced Organic Materials for Nonmetallic Charge Carrier-Based Batteries

Organic electrode materials(OEMs),withmerits of structural diversity,molecular-level controllability,resource abundance,and environmental friendliness,have become a promising electrode candidate for low-carbon renewable batteries.Safer,environmentally benign,and sustainable aqueous rechargeable batteries are particularly appealing for large-scale energy storage applications.This review aims to provide an insightful discussion of OEMs in nonmetallic charge carrier-based batteries,especially for the application in aqueous rechargeable systems.The emerging application of OEMs in versatile aqueous batteries will be analyzed emphatically,including aqueous proton batteries,aqueous ammonium-ion batteries,and air self-charging batteries.We expect that this review can serve as a guide for the future development of OEMs in nonmetallic charge carrier-based batteries and provide inspiration for unmet challenges.

Effects of BTA2 as the third component on the charge carrier generation and recombination behavior of PTB7:PC71BM photovoltaic system

Effects of a benzotriazole(BTA)-based small molecule,BTA2,as the third component on the charge carrier generation and recombination behavior of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]](PTB7):[6,6]-phenyl-C71-butyric acid methyl ester(PC71BM)organic solar cells(OSCs)were investigated by optical simulation of a transfer matrix model(TMM),photo-induced charge extraction by linearly increasing voltage(photo-CELIV)technique,atomic force microscope(AFM),and the Onsager–Braun model analysis.BTA2 is an A_(2)-A_(1)-D-A_(1)-A_(2)-type non-fullerene small molecule with thiazolidine-2,4-dione,BTA,and indacenodithiophene as the terminal acceptor(A_(2)),bridge acceptor(A_(1)),and central donor(D),respectively.The short-circuit current density of the OSCs with BTA2 can be enhanced significantly owing to a complementary absorption spectrum.The optical simulation of TMM shows that the ternary OSCs exhibit higher internal absorption than the traditional binary OSCs without BTA2,resulting in more photogenerated excitons in the ternary OSCs.The photo-CELIV investigation indicates that the ternary OSCs suffer higher charge trap-limited bimolecular recombination than the binary OSCs.AFM images show that BTA2 aggravates the phase separation between the donor and the acceptor,which is disadvantageous to charge carrier transport.The Onsager-Braun model analysis confirms that despite the charge collection efficiency of the ternary OSCs being lower than that of the binary OSCs,the optimized photon absorption and exciton generation processes of the ternary OSCs achieve an increase in photogenerated current and thus improve power conversion efficiency.

Visible-light-driven heterostructured g-C_(3)N_(4)/Bi-TiO_(2) floating photocatalyst with enhanced charge carrier separation for photocatalytic inactivation of Microcystis aeruginosa

The increase in occurrence and severity of cyanobacteria blooms is causing increasing concern;moreover,human and animal health is affected by the toxic effects of Microcystin-LR released into the water.In this paper,a floating photocatalyst for the photocatalytic inactivation of the harmful algae Microcystis aeruginosa(M.aeruginosa)was prepared using a simple sol-gel method,i.e.,coating g-C_(3)N_(4) coupled with Bi-doped TiO_(2) on Al_(2)O_(3)-modified expanded perlite(CBTA for short).The impact of different molar ratios of Bi/Ti on CBTA was considered.The results indicated that Bi doping in TiO_(2) inhibited photogenerated electron-hole pair recombination.With 6 h of visible light illumination,75.9%of M.aeruginosa(initial concentration=2.7106 cells/L)and 83.7%of Microcystin-LR(initial concentration=100μg/L)could be removed with the addition of 2 g/L CBTA1%(i.e.,Bi/Ti molar ratio=1%).The key reactive oxygen species(ROSs)in the photocatalytic inactivation process are h+andOH.The induction of the Bi^(4+)/Bi^(3+)species by the incorporation of Bi could narrow the bandgap of TiO_(2),trap electrons,and enhance the stability of CBTA-1%in the solutions with coexisting environmental substances.

Significantly influenced photocatalytic performance for H_(2)O_(2)generation over ultrathin g-C_(3)N_(4)through regulating the migration orientation of photogenerated charge carriers

H_(2)O_(2)has been widely applied in the fields of chemical synthesis,medical sterilization,pollutant removal,etc.,due to its strong oxidizing property and the avoidable secondary pollution.Despite of the enhanced performance for H_(2)O_(2)generation over g-C_(3)N_(4)semiconductors through promoting the separation of photo-generated charge carriers,the effect of migration orientation of charge carriers is still ambiguous.For this emotion,surface modification of g-C_(3)N_(4)was employed to adjust the migration orientation of charge carriers,in order to investigate systematically its effect on the performance of H_(2)O_(2)generation.It was found that ultrathin g-C_(3)N_(4)(UCN)modified by boron nitride(BN),as an effective hole-attract agent,demonstrated a significantly enhanced performance.Particularly,for the optimum UCN/BN-40%catalyst,4.0-fold higher yield of H_(2)O_(2)was obtained in comparison with the pristine UCN.As comparison,UCN modified by carbon dust demonstrated a completely opposite tendency.The remarkably improved performance over UCN/BN was ascribed to the fact that more photo-generated electrons were remained inside of triazine structure of g-C_(3)N_(4),leading to the formation of larger amount of 1,4-endoxide.It is anticipated that our work could provide new insights for the design of photocatalyst with significantly improved performance for H_(2)O_(2)generation.

Unravelling charge carrier dynamics in protonated g-C3N4 interfaced with carbon nanodots as co-catalysts toward enhanced photocatalytic CO2 reduction： A combined experimental and first-principles DFT study

In this work, we demonstrated the successful construction of metal-free zero- dimensional/two-dimensional carbon nanodot （CND）-hybridized protonatedg=C3N4 （pCN） （CND/pCN） heterojunction photocatalysts b; means of electrostatic attraction. We experimentally found that CNDs with an average diameter of 4.4 nm were uniformly distributed on the surface of pCN using electron microscopy analysis. The CND/pCN-3 sample with a CND content of 3 wt.% showed thehighest catalytic activity in the CO2 photoreduction process under visible and simulated solar light. This process results in the evolution of CH4 and CO. Thetotal amounts of CH4 and CO generated by the CND/pCN-3 photocatalyst after 10 h of visible-light activity were found to be 29.23 and 58.82 molgcatalyst-1, respectively. These values were 3.6 and 2.28 times higher, respectively, than thearn＊ounts generated when using pCN alone. The corresponding apparent quantum efficiency （AQE） was calculated to be 0.076%. Furthermore, the CND/pCN-3 sample demonstrated high stability and durability after four consecutive photoreaction cycles, with no significant decrease in the catalytic activity.