Charge Carrier Dynamics Research Articles

Enhanced Photoelectrochemical Water Splitting of In2S3 Photoanodes by Surface Modulation with 2D MoS2 Nanosheets.

Photoanodes with ample visible-light absorption and efficient photogenerated charge carrier dynamics expedite the actualization of high-efficiency photoelectrochemical water splitting (PEC-WS). Herein, we fabricated the heterojunction nanostructures of In2S3/MoS2 on indium-doped tin oxide glass substrates by indium sputtering and sulfurization, followed by the metal-organic chemical vapor deposition of 2D MoS2 nanosheets (NSs). The photocurrent density of In2S3/MoS2 was substantially enhanced and higher than those of pristine In2S3 and MoS2 NSs. This improvement is due to the MoS2 NSs extending the visible-light absorption range and the type-II heterojunction enhancing the separation and transfer of photogenerated electron-hole pairs. This work offers a promising avenue toward the development of an efficient photoanode for solar-driven PEC-WS.

Atomistic insight into the device engineering of inorganic halide perovskite solar cells

Perovskites provide a promising pathway for fabricating efficient and lightweight solar cells, which could be game-changers in the renewable energy landscape. Yet, the phase stability and device design are still the key issues of perovskite-based photovoltaics. Herein, we evaluated the phase stability of CsPbX3 (X = I, Br, and Cl) upon analyzing the lattice dynamics from first-principles and then predicted fundamental properties including bandgap, carrier mobility, and optical absorption as input to optimize the device design of solar cell. A maximum power conversion efficiency (PCE) of 12.36 % was achieved for a CsPbBr3-based solar cell. Those findings highlight the potential of CsPbX3 perovskites for high-efficiency solar cells. The computational approach provides a comprehensive understanding of the material's structural stability, charge-carrier dynamics, and optoelectronic characteristics. The collective analysis enables a holistic understanding of CsPbX3 perovskites and provides a roadmap for future advancements in perovskite solar-cell technology.

Visible-Light-Driven Oxidation of Benzene to Phenol with O2 over Photoinduced Oxygen-Vacancy-Rich WO3.

Direct photocatalytic conversion of benzene to phenol with O2 is a green alternative to the traditional synthesis. The key is to find an effective photocatalyst to do the trick. Defect engineering of semiconductors with oxygen vacancies (OVs) is an emerging strategy for catalyst fabrication. OVs can trap electrons to promote charge separation and serving as adsorption sites for O2 activation. However,randomly distribution of OVs on the semiconductor surface often results in mismatching the charge carrier dynamics under irradiation, thus failing to fulfill the unique advantages of OVs for photoredox functions. Herein, we demonstrate that abundant OVs can be facilely generated and precisely located adjacent to the reductive sites on reducible oxide semiconductors such as tungsten oxide (WO3) via a simple photochemistry strategy. Such photoinduced OVs are well suited for photocatalytic benzene oxidation with O2 as they readily capture photogenerated electrons from the reductive sites of WO3 to activate adsorbed O2. 18O-labeling experiments further confirm that the OVs also facilitate the integration of oxygen atoms from O2 into phenol, revealing in detail the pathway for photocatalytic benzene hydroxylation. This study demonstrates that the photochemistry approach is an appealing strategy for the synthesis of high-performance OVs-rich photocatalysts for solar-induced chemical conversion.

Temperature‐Dependent Dynamics of Charge Carriers in Tellurium Hyperdoped Silicon

Temperature‐Dependent Dynamics of Charge Carriers in Tellurium Hyperdoped Silicon

Phenanthridine-based Covalent Organic Frameworks for Boosting Overall Solar H2O2 Production.

Solar-driven H2O2 production via the oxygen reduction reaction (ORR) and water oxidation reaction (WOR) dual channels is green and sustainable, but severely restricted by the sluggish reaction kinetics. Constructing intriguing photocatalysts with effective active centers is a shortcut to breaking the kinetic bottleneck with great significance. Herein, we synthesize two novel neutral phenanthridine-based covalent organic frameworks (PD-COF1 and PD-COF2) for photosynthesizing H2O2. Compared to the no phenanthridine counterpart (AN-COF), the H2O2 photosynthetic activities of PD-COF1 and PD-COF2 are markedly boosted. In air and pure water without sacrificial agents, under Xe lamp and natural sunlight, the H2O2 photogeneration rate of PD-COF2 is 6103 and 3646 μmol g-1 h-1, respectively. Further experimental and theoretical inspections demonstrate that introducing phenanthridine units into COFs smoothly modulates the charge carrier dynamics and thermodynamically favors the generation of crucial OOH* and OH* intermediates in the ORR and WOR paths, respectively. Additionally, this is the first time the neutral phenanthridine moiety serves as the photooxidation unit for 2e- WOR towards H2O2 photoproduction. The current work sheds light on exploring novel catalytic centers for high-performance H2O2 evolution.

Optimizing charge transport simulation for hybrid pixel detectors

To enhance the spatial resolution of the MÖNCH 25 µm pitch hybrid pixel detector, deep learning models have been trained using both simulation and measurement data. Challenges arise when comparing simulation-based deep learning models to measurement-based models for electrons, as the spatial resolution achieved through simulations is notably inferior to that from measurements. Discrepancies are also observed when directly comparing X-ray simulations with measurements, particularly in the spectral output of single pixels. These observations collectively suggest that current simulations require optimization. To address this, the dynamics of charge carriers within the silicon sensor have been studied using Monte Carlo simulations, aiming to refine the charge transport modeling. The simulation encompasses the initial generation of the charge cloud, charge cloud drift, charge diffusion and repulsion, and electronic noise. The simulation results were validated with measurements from the MÖNCH detector for X-rays, and the agreement between measurements and simulations was significantly improved by accounting for the charge repulsion.

Enhanced Schottky barrier engineering in silver-doped TiO2/p-Si heterojunctions: Insights into electrical behavior and charge carrier dynamics

Heterojunctions were fabricated through the deposition of silver-doped Titanium dioxide (Ag–TiO2) onto p-type crystalline silicon, employing the sol-gel technique. Electrical characterization was conducted with varying Ag concentrations. The investigation revealed that the Schottky barriers at each interface (Ag/TiO2 and Si/Ag), along with the built-in potential at the TiO2/p-Si junction, increase proportionally with the Ag concentration. This observed trend was attributed to the reduction in the TiO2 bandgap due to Ag incorporation, resulting in a concurrent shift in both valence and conduction bands. Consequently, there is a growth of the conduction energy discontinuity and a reduction in the valence one, facilitating hole diffusion while impeding electron transfer across the depletion layer. Furthermore, the introduction of Ag leads to a decrease in both electron and hole concentrations. However, Ag incorporation within the TiO2 matrix manifests as nanoparticles and clusters, resulting in a nonhomogeneous distribution of charge carriers across the sample. Impedance analysis indicates an increase in device resistance and a decrease in effective capacitance.

Facilitating exciton dissociation in conjugated microporous polymers for photocatalytic degradation of tetracycline via a gradient N doping strategy

As a leading green wastewater treatment technology, organic semiconductor photocatalysis for tetracycline (TC) degradation is widely recognized but currently constrained by excessive exciton binding energies and rapid charge recombination. In this work, conjugated microporous polymers (CMPs) with five-membered heterocyclic ring have been fabricated by gradient doping of nitrogen at the monomer level. It demonstrates satisfactory photocatalytic performance, with thiadiazole introduced into the unit, achieving a TC removal rate of 95.6% within 30 min under visible light. The underlying origin of the preferable property lies in the lower exciton binding energy (Eb) with the assistance of the donor–acceptor (D-A) structure constructed by thiadiazole monomer and triazine skeleton. Density Functional Theory (DFT) calculations reveal that this five-membered heterocyclic structure can appropriately regulate the local charge distribution and increase the dipole moment, thus accelerating the migration dynamics of charge carriers in the degradation process. This study provides a novel insight into the modulation of polymer exciton Eb and enlightens the designation of metal-free photocatalysts based on antibiotic degradation.

Charge carrier dynamics of chemical vapor deposited carbon-doped titanium dioxide photoanodes

This study explores the synthesis of carbon-doped titanium dioxide TiO2(C) photoanodes through a single-step, low-pressure chemical vapor deposition (LCPVD) method, investigating the influence of carbon doping and oxygen vacancies on photoelectrochemical performance. The research employs morphological, structural, and photoelectrochemical characterization methods, including intensity-modulated photocurrent spectroscopy (IMPS) and distribution of relaxation times (DRT) analysis. We correlate the simultaneous presence of surface carbon and oxygen defects to improved charge separation and collection for TiO2(C) photoanodes. This work provides a comprehensive and detailed explanation of the photoelectrochemical performance of TiO2 electrodes, showing the potential behind combined IMPS-DRT analysis for photoelectrode characterization.

Unravelling charge carrier dynamics for enhancement of photocatalytic performance in Pd/MoS2 nanocomposites for water remediation of real-world pollutants

In this study, Pd/MoS2 nanocomposites were successfully synthesized incorporating Pd nanoparticles into three-dimensional (3D) flower-like MoS2 nanostructures. The controlled introduction of Pd was aimed to optimize the photocatalytic performance of the resulting nanocomposites, which exhibited exceptional efficiency in degrading various organic pollutants and antibiotic tetracycline (TC) under simulated solar light irradiation. The nanocomposites with an optimized Pd concentration of 2.5 % demonstrated outstanding photocatalytic efficiency, achieving the degradation of Rhodamine B (RhB), Methylene blue (MB), TC by 98 %, 98 %, and 96 %, respectively, with specific interval of 40, 30 and 60 min. The reaction rate constant of the Pd/MoS2 nanocomposites was measured to be 0.7798 min−1 using pseudo first-order rate kinetics. The value is about 19 times higher than that of pure MoS2 (0.00414 min−1) for degradation of RhB. The improved photocatalytic performance of these nanocomposites can be attributed to several factors. Firstly, the incorporation of Pd nanoparticles substantially enhanced their light absorption capabilities, leading to an overall increase in photocatalytic efficiency. Moreover, the presence of Pd contributed to a large surface area, further enhancing the nanocomposite's photocatalytic potential. Importantly, the formation of a built-in electric field at Pd/MoS2 interface facilitated the efficient separation of the electron-hole pairs, extending the life time of these photoinduced charge carriers. This study offers valuable insights into development of MoS2-based photocatalyst, which hold significant promise for addressing water pollution challenges and making substantial contributions to the field of water purification and environmental remediation.

Improvement of X-ray response of CZT films by post-annealing

CdZnTe (CZT) epitaxial films are promising for X-ray flat panel detectors due to their ability for large area fabrication, high absorption efficiency, and excellent detective quantum efficiency (DQE). However, challenges like image lag, ghosting, and reduced DQE due to long response times and high dark currents persist. This study introduces a novel post-in-situ annealing technique to enhance CZT film sensitivity and transient response. Results show that a brief 20 s annealing treatment increased surface Zn content, raising detector resistivity from 3.5 × 109 Ω·cm to 3.3 × 1010 Ω·cm while reducing leakage current at high voltages. This treatment also significantly reduced surface defects, improving CZT film detectors’ X-ray response time. Moreover, the electrons mobility-lifetime product (μτ)e improved from 2.30 × 10−5 cm2/V to 2.17 × 10−4 cm2/V, indicating enhanced charge carrier dynamics crucial for high-speed X-ray detection. Notably, the X-ray response sensitivity achieved a commendable 126 μC G−1· cm−2 a bias of 30 V. In conclusion, in-situ annealing represents a remarkable step forward in the development of CZT technology for X-ray flat panel imaging, addressing critical issues and potentially broadening its applications in medical and industrial imaging systems.

Positional Isomerism of Aromatic Heterocyclic Spacer Cations in Two-Dimensional Dion-Jacobson Hybrid Perovskites.

Ligand engineering of aromatic heterocyclic cations in two-dimensional (2D) Dion-Jacobson (DJ) perovskites has been widely explored in recent years. In this study, how the positional isomers of aromatic heterocyclic cations tune the lattice of 2D perovskites, thereby influencing the transport and recombination dynamics of charge carriers, has been investigated through nonadiabatic molecular dynamics simulations. We demonstrate that the meta-substituted 3-(aminomethyl)pyridinium (3AMPY) cations greatly reduce the strength of electron-vibration coupling since the strong hydrogen-bonding network introduced by the changes in the arrangement of spacer cations significantly suppresses the structural thermal fluctuations. Compared to the para-substituted 4-(aminomethyl)pyridinium (4AMPY) cation, using the asymmetric 3AMPY as a spacer cation can achieve improved in-plane transport performance, enhanced thermal stability, and suppressed charge carrier recombination through weakening electron-vibration interactions. Our results explain the observed lifetime difference between the two types of DJ-phase perovskites in experiments and provide new guidance for optimizing the performance of perovskite devices.

Efficient Polycrystalline Single-Cation Perovskite Light-Emitting Diodes by Simultaneous Intracrystal and Interfacial Defect Passivation.

Polycrystalline perovskite light-emitting diodes (PeLEDs) have shown great promise with high efficiency and easy processability. However, PeLEDs using single-cation polycrystalline perovskite emitters have demonstrated low efficiency due to defects within the grains and at the interfaces between the perovskite layer and the charge injection contact. Thus, simultaneous defect engineering of perovskites to suppress exciton loss within the grains and at the interfaces is crucial for achieving high efficiency in PeLEDs. Here, 1,8-octanedithiol which is a strong nucleophile, is used to increase the luminescence efficiency of a single-cation perovskite by suppressing non-radiative recombination within the grains of their polycrystalline emitter film as well as at their interface with an anode. The dithiol additive performs a multifunctional role in defect passivation, spatial confinement of excitons, and prevention of exciton quenching at the interface between the perovskite layer and the underlying hole-injection layer. Photoluminescence studies demonstrate that incorporating the dithiol additive significantly enhances the charge carrier dynamics in perovskites, resulting in an external quantum efficiency (EQE) of up to 23.46% even in a simplified PeLED that does not use a hole-injection layer. This represents the highest level of EQE achieved among devices utilizing polycrystalline single-cation perovskites.

Multi-species defect engineering synergistic localized surface plasmon resonance boosting photocatalytic CO2 reduction

Inadequate charge carrier kinetics and a scarcity of active sites still challenge photocatalytic CO2 reduction reaction (CO2RR). We exploit the synergy between multi-species defect engineering and the localized surface plasmon resonance (LSPR) effect in Bi/BiV1-mO4-m to address these limitations. Theoretical calculations show that V and O defects collectively modulate the work function of BiVO4, which induces hot electrons to transfer from Bi nanoparticles to BiV1-mO4-m. These electrons are then captured by O defects, confirmed by femtosecond transient absorption spectroscopy. Electron density is significantly increased at the O defects, enhancing CO2 adsorption and establishing it as a new reaction site. Bi/BiV1-mO4-m achieves photocatalytic CO2RR in pure water; Bi/BiV1-mO4-m achieves direct solar-driven photocatalytic CO2RR with a CO yield of 501 μmol/g/h under concentrated sunlight.

Transient Electroluminescence Spectroscopy in Planar Electroluminescent Devices

AbstractThe emergence of planar electroluminescent diodes (including polymer light‐emitting diodes, organic light‐emitting diodes, quantum‐dot light‐emitting diodes, and perovskite light‐emitting diodes) is causing a revolution in displays, lighting, and wearable electronic devices. Continuous advancement in the comprehension and management of charge carrier dynamics in these devices has led to several significant breakthroughs, including diodes with ultrahigh luminance, memory devices, and amplified spontaneous emission. Transient electroluminescence (TrEL) spectroscopy is a relative powerful technology to investigate charge dynamics, including transport, distribution, and storage of charge carriers, in electrically‐driven planar light‐emitting diodes (LEDs). The aim of this review is to revisit the principle and applications of TrEL spectroscopy in planar electroluminescent diodes, and to evaluate the reliability of various parameters extracted using this technology. A particular focus is on electroluminescence response time, charge‐carrier transport and storage, and exciton species. First, the principle and equipment system of the TrEL, as well as specific attention during TrEL measurements are described in detail, following by the applications TrEL spectroscopy in planar LEDs. Further development on the TrEL technology is discussed in the third section. Finally, a summary and outlook for the TrEL are shown and challenges faced by the TrEL spectroscopy are also highlighted.

Charge Carrier Dynamics in Bandgap Modulated Covellite-CuS Nanostructures.

Copper Sulfide (CuS) semiconductors have garnered interest, but the effect of transition metal doping on charge carrier kinetics and bandgap remains unclear. In this study, the interactions between dopant atoms (Nickel, Cobalt, and Manganese) and the CuS lattice using spectroscopy and electrochemical analysis are explored. The findings show that sp-d exchange interactions between band electrons and the dopant ions, which replace Cu2+, are key to altering the material's properties. Specifically, these interactions result in a reduced bandgap by shifting the conduction and valence band edges and increasing carrier concentration. It is observed that undoped CuS nanoflowers exhibit a carrier lifetime of 2.16 ns, whereas Mn-doped CuS shows an extended lifetime of 2.62 ns. This increase is attributed to longer carrier scattering times (84 ± 5 fs for Mn-CuS compared to 53 ± 14 fs for CuS) and slower trapping (∼1.5 ps) with prolonged de-trapping (∼100 ps) rates. These dopant-induced energy levels enhance mobility and carrier lifetime by reducing recombination rates. This study highlights the potential of doped CuS as cathode materials for sodium-ion batteries and emphasizes the applicability of metal sulfides in energy solutions.

Ultrafast Interfacial Charge Transfer in Anisotropic One-Dimensional CsPbBr3/Pt Epitaxial Heterostructure.

Colloidal one-dimensional (1D) perovskite nanorods (NRs) and metal epitaxial heterostructures (HSs) are the promising class of new materials for efficient photovoltaic and photocatalytic applications. Besides, fundamental photophysical properties and its device applications of 1D perovskite-metal HSs are limited due to their challenging synthetic protocols and difficulties in forming epitaxial growth between covalent and ionic bonds. Herein, we have synthesized the CsPbBr3 perovskite NRs-platinum (Pt) nanoparticles (NPs) (CsPbBr3/Pt) epitaxial HS using cation exchange followed by chemical reduction methods with the orthorhombic Cs2CuBr4 NRs. Here, the tertiary ammonium ions extensively helped to form the 1D Cs2CuBr4, CsPbBr3 NRs, and CsPbBr3/Pt HSs. For CsPbBr3/Pt HSs an epitaxial relationship has been established in the (020) plane of orthorhombic CsPbBr3 with the (020) plane of cubic Pt. Further, femtosecond transient absorption (TA) spectroscopy was employed to study the charge carrier dynamics of CsPbBr3/Pt HS. Upon 420 nm photoexcitation, excitons in the conduction band of CsPbBr3 NRs dissociate by electron transfer (with an ultrafast time of 1.1 ps) to the Pt domain. In addition, charge transfer (CT) was also demonstrated in the CsPbBr3/Pt HS, which is ascribed to strong electron coupling and epitaxial growth between CsPbBr3 and Pt states. This extensive understanding of the electron transfer dynamics of CsPbBr3/Pt epitaxial HS may pave the way to designing highly efficient photovoltaic and photocatalytic applications.

Photocatalytic water splitting and charge carrier dynamics of Janus PtSSe/ζ-phosphorene heterostructure

On the basis of first-principles calculations and non-adiabatic molecular dynamics (NAMD) simulations, we explore the photocatalytic water splitting properties of PtSSe/ζ-Phosphorene heterostructure. This heterostructure possess semiconducting nature with high carrier mobility (≈ 103 cm2V− 1s− 1). The calculated high value of electron-hole recombination rate as compared to electron transfer rate and hole transfer rate, establish the Type-II mechanism more favorable for PtSSe/ζ-Phosphorene heterostructure. Further, the calculated value of solar-to-hydrogen (STH) conversion efficiency of PtSSe/ζ-Phosphorene exceeds to 10%, which makes it the potential candidate for commercial production of hydrogen for industrial use. STH conversion efficiency is further tunable on rotating one monolayer over other with specific angles in the heterostructure. Our study demonstrates PtSSe/ζ-Phosphorene heterostructure to be efficient Type II-scheme photocatalyst for water splitting.

Probing Defects in Covalent Organic Frameworks.

Defects in covalent organic frameworks (COFs) play a pivotal role in determining their properties and performance, significantly influencing interactions with adsorbates, guest molecules, and substrates as well as affecting charge carrier dynamics and light absorption characteristics. The present review focuses on the diverse array of techniques employed for characterizing and quantifying defects in COFs, addressing a critical need in the field of materials science. As will be discussed in this review, there are basically two types of defects referring either to missing organic moieties leaving free binding groups in the material or structural imperfections resulting in lower crystallinity, grain boundary defects, and incomplete stacking. The review summarizes an in-depth analysis of state-of-the-art characterization techniques, elucidating their specific strengths and limitations for each defect type. Key techniques examined in this review include powder X-ray diffraction (PXRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), scanning transmission electron microscopy (STEM), scanning tunneling microscope (STM), high resolution transmission electron microcoe (HRTEM), gas adsorption, acid-base titration, advanced electron microscopy methods, and computational calculations. We critically assess the capability of each technique to provide qualitative and quantitative information about COF defects, offering insights into their complementary nature and potential for synergistic use. The last section summarizes the main concepts of the review and provides perspectives for future development to overcome the existing challenges.

Ultrafast photoinduced charge carrier dynamics of L-cysteine and oleylamine stabilized CsPbBr3 perovskite quantum dots coupled with gold nanoparticles.

We have synthesized L-cysteine and oleylamine stabilized CsPbBr3 perovskite quantum dots (PQDs) and coupled them with gold nanoparticles (AuNPs). The PQDs and AuNPs, as well as their hybrid nanostructures (HNS), were characterized using UV-visible (UV-vis) and photoluminescence (PL) spectroscopy. The UV-vis spectra show absorption bands of the HNS at 503 and 520nm, attributed mainly to PQDs and AuNPs, respectively. The PQDs show a strong excitonic PL band peaked at 513nm from PQDs. The HR-TEM results show the formation of hybrid structures between PQDs and AuNPs, which is also supported by the PL quenching of the PQDs by the coupled AuNPs. Ultrafast dynamics of the exciton and charge carriers in the HNS and pristine PQD were studied using femtosecond transient absorption. Multiexponential fitting of the dynamic data revealed the existence of shallow and deep trap states in pristine PQDs and ultrafast electron transfer from PQDs to AuNPs in the HNS. A kinetic model was proposed to account for the key dynamic processes involved and to extract the time for electron transfer from PQDs to AuNPs in the HNS, found to be ∼2ps. Dynamic processes in pristine PQDs are largely unchanged by HNS formation with AuNPs.