Carrier Lifetime Research Articles

Influence of MACl on the Crystallization Kinetics of Perovskite via a Two-Step Method

The addition of methylammonium chloride (MACl) significantly improves the performance and stability of perovskite fabricated by two-step processes. However, its role in crystallization dynamics has not been thoroughly studied. In this work, a comparison study is carried out using different additions of MACl to investigate the impact of the perovskite crystallization dynamics. In situ grazing incidence wide-angle X-ray scattering (GIWAXS) observations during the annealing process of perovskite revealed that the amount of MACl significantly influences the crystallinity and orientation of the perovskite. Increasing the MACl addition enhances the crystallinity of the perovskite in the wet film‘s intermediate phase and strengthens the out-of-plane orientation of the FAPbI3 perovskite α-phase (001) planes during annealing. Moreover, it was found that both excessive and insufficient amounts of MACl introduce defects into the perovskite, which are detrimental to device performance. In contrast, an optimal ratio of MACl-9 mg leads to the formation of uniform and large-grained FAPbI3 perovskite films, with the longest carrier lifetimes (163.7 ns) compared to MACl-5 mg (68.4 ns) and MACl- 13 mg (120.1 ns). As a result, the fabricated MACl-9 mg-based solar cell achieved the highest efficiency (22.63%), which is higher than those of MACl-5 mg (21.47%) and MACl-13 mg (20.07%).

Anomalous X-ray pulse responses in MAPbBr3 single crystal-based detectors

Organic-inorganic perovskite single crystals (SCs) are considered promising semiconductors for high-sensitivity X-ray detectors because of their strong X-ray interaction, low-temperature processability, and excellent properties such as long diffusion length, low defect density, and long carrier lifetime. However, the specific pulse response of MAPbBr3 SC-based X-ray detectors frequently exhibits a tail and over/undershoots at several conditions, which degrades the X-ray image quality; however, no detailed analysis of these characteristics has been reported thus far. For high-resolution X-ray imaging, it is necessary to obtain an ideal pulse response that is free of tails and over/undershoots. In this study, we investigated the specific X-ray responses of solution-grown MAPbBr3 SC-based X-ray detectors under various externally applied voltages. Based on the study on charge carrier dynamics, we analyzed the origin of the tail and over/undershoots in X-ray pulse response shapes. We theoretically verified that the unideal pulse response in perovskite SC-based X-ray detectors is attributed to the defect states inherent in perovskite SCs.

Promoting the optoelectronic and nonlinear optics properties of MoS2 nanosheets via metal Al anchoring

Molybdenum disulfide (MoS2) has attracted much attention in the field of optoelectronic materials due to its stability and adjustable bandgap structure. However, improving the optoelectronic properties of MoS2 is still a challenging research. Herein, Al doped MoS2 (AMS) films were prepared by a simple single-step magnetron sputtering method. The bonding modes of Al implantation and auxiliary MoS2 were investigated by adjusting metal Al anchoring. The successful synthesis of AMS films was confirmed by the analysis of X-ray diffraction and X-ray photoelectron spectroscopy measurements to investigate the diffraction peaks of Al and Al2S3 and the valence electron structures of Al3+. Compared to MoS2, the A1g Raman peaks of AMS films are slightly blue-shifted, and the peak positions of both Mo3d and S2p are slightly shifted towards higher binding energies. This is attributed to the surface plasmon resonance effect produced by Al doping resulting in a large amount of electron transfer to the conduction band (CB) of MoS2. In addition, the density functional theory calculations reveal that Al doping of MoS2 results in a higher concentration of electrons in CB of MoS2, the band gap of MoS2 can be adjusted by changing the doping concentration of Al. The Z-scan results illustrated that MoS2 was converted from saturable absorption to reverse saturable absorption (RSA) by adjusting the sputtering power of Al. This is attributed to the fact that Al doping increases the electron concentration in the CB of MoS2, which promotes the RSA of the excited states and doping energy levels of AMS films. The values of the nonlinear absorption coefficients of AMS films are 2–5 times higher than those of MoS2, which significantly improves the nonlinear absorption performance of MoS2. The carrier relaxation process and kinetic mechanism of AMS films were investigated by transient absorption spectroscopy, moderate doping of Al can effectively improve the carrier lifetime. This implies that AMS films have good optoelectronic properties and have a wide application potential in optoelectronic devices.

Ligand modulation of active center to promote lead-free Cs2AgInCl6 photocatalytic CO2 reduction

Metal halide perovskites (MHP) are potential candidates for the photocatalytic reduction of CO2 due to their long photogenerated carrier lifetime and charge diffusion length. However, the conventional long-chain ligand impedes the adsorption and activation of CO2 molecules in practical applications. Here, a ligand modulation technology is employed to enhance the photocatalytic CO2 reduction activity of lead-free Cs2AgInCl6 microcrystals (MCs). The Cs2AgInCl6 MCs passivated by Oleic acid (OLA) and Octanoic acid (OCA) are used for photocatalytic CO2 reduction. The results show that the surface defects and electronic properties of Cs2AgInCl6 MCs can be adjusted through ligand modulation. Compared with the OLA-Cs2AgInCl6, the OCA-Cs2AgInCl6 catalyst demonstrated a significant improvement in the catalytic yield of CO and CH4. The CO and CH4 catalytic yields of OCA-Cs2AgInCl6 reached 171.88 and 34.15 µmol g−1 h−1 which were 2.03 and 12.98 times higher than those of OLA- Cs2AgInCl6, and the total electron consumption rate of OCA-Cs2AgInCl6 was 615.2 µmol g−1 h−1 which was 3.25 times higher than that of OLA-Cs2AgInCl6. Furthermore, in situ diffuse reflectance infrared Fourier transform spectra revealed the enhancement of photocatalytic activity in Cs2AgInCl6 MCs induced by ligand modulation. This study illustrates the potential of lead-free Cs2AgInCl6 MCs for efficient photocatalytic CO2 reduction and provides a ligand modulation strategy for the active promotion of MHP photocatalysts.

Silane Doping for Efficient Flexible Perovskite Solar Cells with Improved Defect Passivation and Device Stability.

In this work, doping 3-amino-propyl triethoxysilane (APTES) into a perovskite precursor is proven to be an effective strategy, which can passivate crystal defects, control the crystallization rate, and improve the morphology. APTES can form oligomers through hydrolysis and a condensation reaction, thus blocking the invasion of external water molecules. In addition, the lone pair electrons on the N atom in the amino group of APTES form a coordination bond with perovskite by sharing the empty 6p orbital on Pb2+, which can effectively passivate the defects of the film and realize a highly uniform and dense perovskite film with preferential crystal growth orientation. The film exhibits high (110) crystal plane orientation and long carrier lifetime and mobility, which improves the performance of flexible perovskite solar cells. Using this approach, the champion device presents an optimal power conversion efficiency of 19.84% with much promoted air stability. Moreover, the efficiency of flexible devices does not decrease after maximum power point irradiation for 360 s.

Electrochemical synthesis of hierarchical porous PbSe film and its infrared photodetection properties

Lead selenide (PbSe) has been extensively studied as an infrared detection material capable of operating at room temperature. In this research, we proposed a simple cyclic voltammetry (CV) electrodeposition of hierarchical porous PbSe on single-layer graphene film. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy were used to evaluate the physical and surface characteristics of porous PbSe films. The porous structure with large surface to volume ratio will enhance the light absorption ability after effectively sensitized in oxygen atmosphere. Furthermore, oxygen-sensitized processes create electron traps at grain boundaries, extending the lifetime of the hole carrier and improving photoconductive sensitivity. At room temperature, the porous PbSe/graphene photodetector exhibit a responsivity of 12.3 A/W, a detectivity of 5.95 * 108 cm Hz1/2W−1 (@1 kHz) at 1.55 µm, and a responsivity of 15.2 A/W, a detectivity of 1.4 * 109 cm Hz1/2W−1(@1 kHz) at 2.7 µm. This work highlights the low cost and effective electrodeposition strategy for constructing hierarchical porous structure with further application in infrared photodetection.

Effect of films thickness and hydrogen annealing on passivation performance of plasma ALD based Hafnium oxide films

We investigate the silicon surface passivation property of Plasma Atomic Layer Deposited (PALD) hafnium oxide thin films and study its dependence on silicon (Si) doping type, film thickness, and post-deposition annealing conditions. Our results demonstrate that as-deposited HfOx films exhibit poor passivation quality that can be improved by performing post-deposition annealing at 450 °C in hydrogen ambient. We demonstrate that the films can effectively passivate p-Si surfaces as compared to n-Si, where the surface passivation quality of the films improves with increasing film thickness for both silicon doping types. The best performance with a minority carrier lifetime of 1.7 ms, corresponding surface recombination velocity (SRV) ∼10 cm s−1, is achieved for HfOx films thickness ∼23 nm deposited on the p-Si substrate. The Capacitance-Voltage (C–V) measurements give an insight into the passivation mechanism of the studied films. Field effect passivation is found to be an important passivation mechanism in PALD-deposited HfOx films, as revealed by C–V measurements. The films are also characterized using Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS), which reveals the chemical passivation provided by hydrogen ambient annealing. Overall, the impact of hafnium oxide film thickness and hydrogen ambient annealing conditions on silicon surface passivation is investigated. Our findings will help in utilizing plasma ALD process based HfOx films for silicon solar cell device application.

A comparative study on the impact of preparation technique on the minority carrier lifetime of Cu2O absorber

A comparative study on the impact of preparation technique on the minority carrier lifetime of Cu2O absorber

Boosting the Carrier Lifetime and Optical Activity of CsPbX3 Nanocrystals through Aromatic Ligand Passivation.

Ligand engineering is crucial for tuning the structural and optoelectronic properties of perovskite nanocrystals (NCs), which also improves their stability. In contrast to the typically used long-chain alkylamine ligands, we successfully introduced an aromatic 1-(p-tolyl)ethylamine (PTEA) ligand to synthesize the CsPbX3 (X = Br or I) NCs. The CsPbI3 and CsPbBr3 NCs demonstrated long carrier lifetimes of ∼877 and 49 ns, respectively, as well as high photoluminescence quantum yields (PLQYs) of ∼99% and 95%, respectively. Furthermore, such NCs realized excellent long-term stability in an ambient atmosphere without obvious degradation over one month. All of these properties were better than the properties of NCs coated with the conventional alkylamine ligands. The high performance of these NCs was discussed with the effective surface passivation by PTEA. Our finding suggests a facile and effective ligand (PTEA) for modulating perovskites, achieving enhancement of both the carrier lifetime and the PLQY.

Enhancing carrier collection in CsPbBr3 solar cells through crystal orientation and defect passivation

All-inorganic carbon-based CsPbBr3 perovskite solar cells (PSCs) have gained growing interest for their remarkable stability. However, compared to their organic–inorganic hybrid counterparts, there is still substantial room for improving their performance primarily due to the inferior photogenerated carrier collection efficiency. Here, we employ area-dependent transient photocurrent to assess the carrier transit time in CsPbBr3 PSCs, revealing that an extended carrier transit time relative to the lifetime significantly contributes to their low carrier collection efficiency. To address this challenge, we narrow the gap between carrier transit time and lifetime by introducing a dual-functional additive, serving to facilitate both crystallization orientation and defect passivation. Consequently, we achieve enhanced short-circuit current and efficiency in CsPbBr3 PSCs.

Enhanced CO2 photoreduction to CO by small-size NH2-UiO-66 nanoparticles immobilization on Mo2C

The small-size and efficient charge separation of MOFs catalysts are essential for improving photocatalytic performance. In this work, a series of small-size NH2-UiO-66 nanoparticle-modified Mo2C photocatalysts were successfully prepared by hydrothermal synthesis with in situ growing NH2-UiO-66 on the surface of Mo2C. The addition of Mo2C can not only obtain small-size NH2-UiO-66 nanoparticles, but also significantly increase the separation efficiency of photo-generated carriers and prolongs the carrier lifetime, thereby promoting the photoreduction of CO2 in water vapor with excellent stability. The resulting 11-Mo2C/NH2-UiO-66 (11-MCNU) exhibits excellent catalytic activity for CO2 reduction to CO product at room temperature and atmospheric pressure. The yield of CO can reach 11 μmol g−1 in the absence of organic solvents, sacrifice agents and photosensitizers, which is much higher than that of the isolated NH2-UiO-66 and Mo2C.

Enhancement of photoexcited carrier lifetime in an InGaAs/GaAsP wire-on-well quantum structure investigated by excitation-power-dependent photoluminescence measurements

Enhancement of photoexcited carrier lifetime in an InGaAs/GaAsP wire-on-well quantum structure investigated by excitation-power-dependent photoluminescence measurements

Noticeable influence of V-dopant on optoelectronic properties of ZnO films prepared by SILAR technique

Wide bandgap semiconductors such as Zinc Oxide (ZnO) have earned much attention on account of its interesting optical and electrical properties. Also, doping ZnO with suitable transition elements enables to tune its properties, making it suitable for applications like transparent conducting oxides and LEDs. To this aim, Vanadium-doped ZnO (V:ZnO) thin films are fabricated using the SILAR method and studied the structural, optical, vibrational, photophysical and electrical properties. Introducing vanadium creates lattice relaxation in the ZnO wurtzite structure, influencing its electronic band structure. The X-ray diffraction (XRD) analyses have verified the structural integrity of the vanadium-doped zinc oxide (V:ZnO) films, revealing their polycrystalline composition. The Raman spectroscopy shows the reduced phonon line widths due to the improved crystallite quality with the presence of vanadium. Furthermore, it has been noted that optical characteristics such as the bandgap and refractive index are sensitive to vanadium doping as a consequence of modified electronic structures. Hall-effect experiments have shown that undoped ZnO films possess a mobility of 1.31 cm2/Vs and a charge carrier density of 5.58 × 1013 cm−3. It has been observed that doping with V markedly influences these parameters of ZnO films. Then, the time-resolved photoluminescence measurements reveal the increased carrier lifetimes, suggesting the introduction of dopants mitigates carrier-phonon interactions. Such interactions need to be minimized to prevent the dissipation of carrier energy. In essence, the reported work demonstrates the potential of V:ZnO for optoelectronic applications.

Temperature effect on n-Si/Fe/NiFe photoanodes for the high-efficiency PEC water splitting

Sunlight-driven photoelectrochemical cell (PEC) can utilize water for high-efficiency artificial photosynthesis to produce low-cost green hydrogen fuel. It is crucial to explore the factors affecting the efficiency of PEC water splitting. The ambient temperature of the electrode is yet an important factor that influences PEC performance. Here, n-Si/Fe/NiFe composite photoanodes prepared by electrodeposition exhibited a low onset potential of 0.87 V and a high photocurrent density of 29.70 mA cm−2 (1.23 V vs. RHE) at room temperature, which is superior to those of n-Si/Fe and n-Si/NiFe. The influence of the temperature on the photoelectrochemical properties of n-Si/NiFe was systematically investigated. As the temperature increased, the photocurrent density of n-Si/Fe/NiFe decreased gradually and the oxidation reaction slowed down. Further experiments showed that raising the temperature helps to reduce the interfacial charge transfer resistance, increase the redox potential and carrier density. However, increasing the temperature also increases the recombination rate of photo generated carriers, reduces the carrier lifetime, and thus lowers the performance of PEC. Therefore, adjusting the ambient temperature is a potential method to improve the photoelectrochemical performance of silicon-based photoanodes.

Progress in TOPCon solar cell technology: Investigating hafnium oxide through simulation

In the realm of solar energy technology, exploring hafnium oxide (HfO2) in Tunnel Oxide Passivated Contact (TOPCon) solar cells is pivotal. This study delineates HfO2's evolution from semiconductor applications, highlighting its crucial role in enhancing TOPCon solar cell performance. Utilizing ATLAS Silvaco software, the study anticipates a 21.3% increase in charge carrier lifetime through optimized HfO2 layers, addressing challenges in interface engineering and scalability. Innovative research integrates hafnium oxide (HfO2) into TOPCon solar cells, marking a leap in photovoltaic technology. Utilizing ATLAS Silvaco simulations, it shows that HfO2 layers can significantly enhance cell performance, increasing charge carrier lifetime by 21.3% and potentially boosting efficiency by 25%. This underscores HfO2's advantages, like a higher dielectric constant and thermal stability, in improving solar cell efficiency and durability. Future efforts target refining deposition processes, projecting a 25% boost in overall power conversion efficiency (PCE). Emphasizing HfO2's significance in solar cell technology, this research contributes to global sustainable energy initiatives. Integrating HfO2 in TOPCon solar cells signifies a key achievement in harnessing clean, renewable energy. Upcoming research focuses on experimental validation, interface engineering, optimization, stability assessments, scalability, and collaborative studies, aiming to leverage HfO2's potential for elevating solar energy conversion technologies.

Boosting photocatalytic overall water splitting performance by dual-metallic single Ni and Pd atoms decoration of MoS2: A DFT study

Herein, we propose a novel MoS2 supported single Ni and Pb atoms catalyst (Ni/Pd@MoS2), on which the enhanced efficiency of water splitting is confirmed by quantitative density functional theory (DFT) calculations. The Bader charge, electron density difference (EDD) and projected density of state (PDOS) analysis demonstrates that the moderate electron transfer is reached by the synergy of the Ni atom and the Pd atom. As extra channel for excited carrier migration, the present of defect states obviously prolongs the carrier lifetime (143.45 ps). The unique electronic environment contributes to the electronic synergy and spatially separated of the effective active sites, leading the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) happen smoothly on the Pd and S site, respectively. Our research presents a novel idea for the development of highly efficient diatomic catalysts towards overall water splitting.

Efficient antibiotic degradation catalyzed by oxygen vacancy and Cu-Doped Cu-MOF under visible light

The widespread use of antibiotics in contemporary healthcare has led to their accumulation in natural water systems, contributing to a growing resistance among bacteria and posing a significant challenge to the sustainable development of human society. Photocatalysis has emerged as an effective technique to mitigate antibiotic pollution in water. This study focuses on developing and synthesizing a visible light responsive metal–organic framework (MOF), Cu-NTC, which employs copper as the metal node instead of the usual choice of molybdenum, and the rigid 1,4,5,8-naphthalene tetracarboxylic acid (H4NTC) as the organic ligand. A pivotal step in the synthesis involved the partial reduction of Cu2+, leading to the formation of Cu0/Cu+ doping. This doping, together with oxygen vacancies (OVs), introduces a localized state that functions as a doped energy level, thus prolonging carrier lifetime and enhancing the visible light photocatalytic activity of Cu-NTC. Remarkably, Cu-NTC achieved photocatalytic degradation efficiencies of 84.5 % for tetracycline (TC) and 96.1 % for norfloxacin (NFX) after 30 min in darkness followed by 120 min under visible light exposure. Moreover, Cu-NTC exhibited effective removal capabilities for other antibiotics within the quinolone and tetracycline groups, underscoring their potential for broader applications in water purification.

Methyl-ammonium lead iodide hybrid perovskite thin film as active material for energy conversion devices

The use of hybrid halide Perovskites is helping us get closer to our aim of completely selfsufficient structures in terms of energy production. Preparation of a device of photoactive material CH3NH3PbI3 {FTO (Fluorine-doped tin Oxide)/ CH3NH3PbI3/SpiroOMeTAD/Al} for the photovoltaic applications has been described in this article. Producing a homogeneous thin film through the use of lower temperature, processedsolution devices with one-step spin coating processes is an essential stage in the fabrication process. To generate the thin films on the FTO-substrate, the one-step spin coating approach was utilized for the deposition of the precursor solution, which consisted of methylammonium iodide and lead iodide in a molar ratio of 3:1. This technique was employed to prepare the thin films. The FESEM technique was utilized to carry out the investigation of the surface morphology of this thin layer. In addition, the essential parameters of this device, like barrier height, saturation current, current density, ideality factor, carrier mobility, resistance, carrier lifetime, and capacitance have been computed using current-voltage (I-V) characteristics and the impedance spectroscopy technique. A laser with a power of 20 milliwatts and a wavelength of 532 nanometers was used to light the gadget. The current conduction mechanism exhibits ohmic behavior at a low voltage, while at medium voltages, TFSCLC is the mechanism that regulates charge transportation. Despite the fact that TCSCLC is demonstrated at higher voltages. The TCSCLC model was used to conduct an investigation of the hole's mobility.

Surface-state-related carrier dynamics of GaAs determined by UV-visible pump-probe terahertz spectroscopy

The surface velocity and the bulk lifetime of photo-excited free carriers in GaAs were measured using an optical-pump and THz-probe time-domain technique. By varying the pump laser photon energy from 1.56 to 4.15 eV, we observe that the surface velocity drops abruptly from 0.7×106 cm/s down to 0.2×106 cm/s at 2.5 eV, while the bulk lifetime remains almost constant. We tentatively explain this step-like behavior of the surface velocity vs the photon energy by a trapping of the free carriers at surface states, whose density of states shows a maximum at 2.5 eV.

Effect of Lattice Disorder on Exciton Dynamics in Copper-Doped InP/ZnSexS1-x Core/Shell Quantum Dots.

InP/ZnSexS1-x core/shell quantum dots (QDs) with varying Cu concentrations were synthesized by a one-pot hot-injection method. X-ray diffraction and high-resolution transmission electron microscopy results indicate that Cu doping did not alter the crystal structure or particle size of the QDs. The optical shifts in UV-visible absorption and photoluminescence (PL) suggest changes in the electronic structure and induction of lattice disorder due to Cu doping. Ultrafast transient absorption spectroscopy (TAS) reveled that a higher Cu-doping level leads to faster charge carrier recombination, likely due to increased nonradiative decay from defect states. Time-resolved PL (TRPL) studies show longer average lifetimes of charge carriers with increased Cu doping. These findings informed the development of a kinetic model to better understand how Cu-induced disorder affects charge carrier dynamics in the QDs, which is important for emerging applications of Cu-doped InP/ZnSexS1-x QDs in optoelectronics.