Carrier Lifetime Research Articles

Improvement of mid-wavelength InAs/InAsSb nBn infrared detectors performance through interface control

We report our study to optimize the growth of mid-wavelength InAs/InAsSb nBn infrared detectors through interface control method with AlSb/AlAs superlattices as electron barrier. The dark current model was employed to investigate the dominant dark current mechanism at various operating temperatures. We extracted the minority carrier lifetime of InAs/InAsSb material grown by different interface growth methods. Electrical and optical characterizations indicated superior performance of the device grown by migration-enhanced epitaxy (MEE) with a 3 s As and Sb soak time. With −0.3 V applied bias and 150 K operating temperature, the optimal device shown a dark current density of 8.95 × 10−6 A/cm2 and peak specific detectivity of 7.12 × 1011 cm Hz1/2/W at 3.8 µm.

Effective Dopants Pb and Pb‐SiW12 to Enhance Sb2S3‐based Photodetector Performance

Sb2S3 has excellent photovoltaic properties, but the performance of its photovoltaic devices still needs to be improved. The main issues hindering its photovoltaic performance are the poor carrier transport ability and the significant charge recombination. Doping strategies play a key role in addressing these issues. This study investigates the effect of Pb(CH3COO)2 (Pb) and [Pb(DMF)7]2[SiW12O40] 2DMF (Pb‐SiW12) doping on the photovoltaic properties of Sb2S3 thin films. It is found that the intensity of diffraction peaks on the (130) crystal plane of Pb‐doped Sb2S3 and the (221) crystal plane of Pb‐SiW12@Sb2S3 is increased, which enhances the crystallinity of the films. Meanwhile, Pb and Pb‐SiW12 doping narrow the bandgap (1.69 eV) of Sb2S3 to 1.65 eV and 1.62 eV. Electrochemical tests show that the carrier concentration and carrier lifetime are increased. The Pb‐doped Sb2S3 photodetector photocurrent of 14 μA, 7 times higher than the 2 μA pristine Sb2S3 photodetector. It exhibits a responsivity of 13.9 mA/W and detectivity of 1.2×1011 Jones. The Pb‐SiW12@Sb2S3 photodetector photocurrent is 11 μA. Pb‐SiW12 can immobilize Pb while reducing the amount of Pb. The methodology in this work provides a way to improve the performance of Sb2S3 thin‐film photodetectors.

Suppressed Non-Radiative Recombination in Formamidinium Lead Triiodide under Electric Activation.

The high carrier lifetime of metal halide perovskite (MHP) materials is closely related to the microscopic crystallographic structure. However, the detailed correlation between the lattice structure and carrier dynamics remains unclear. In this work, we found a correlation between lattice strain and open-circuit voltage (Voc) of MHP under electric activation. It is observed that the non-radiative recombination of MHP solar cells is progressively suppressed under elevated residual strain under an electric field. Moreover, the electric activation reduced the density of ions, which permanently switched off the ionic movement in the strained lattice structure. Resultantly, the Voc of cubic formamidinium lead triiodide under electric activation elevated to 1.21 V, which is only 59 mV lower than the theoretical limit of the material. This Voc represents one of the highest values for the same band gap of MHP. This resulted in a high power conversion efficiency (PCE) of 24.15%.

Advancements in CdTe Thin‐Film Solar Cells: Is Doping an Effective Strategy for Performance Enhancement?

Cadmium telluride (CdTe) thin‐film solar cells that are introduced in 1970s have emerged as one of the forefront materials of the second generation‐based solar cells. They are preferred as an ideal candidate for the fabrication of reliable and economical photovoltaic systems owing to high optical absorption coefficient, nearly optimum bandgap for ensuring maximum conversion efficiency and chemical stability. The major challenges associated with these solar cells are low concentration of carriers, which limits the photovoltaic parameters notably the open‐circuit voltage and fill factor as well as short life time of absorber minority carriers. This article explores the pivotal role of doping in enhancing the electrical properties and life time of minority carriers of CdTe solar cells through extensive literature study of the complexity of mechanisms and output parameters achieved in various reported works. Doping has been systematically reviewed with emphasis on types of doping, classification of dopants into group I and group V dopants along with a concise summary of different dopants. This comprehensive review not only evaluates the recent advancements of CdTe solar cells but also addresses these issues and provides future perspectives and paves way for development of improved stable and highly efficient cells.

Regulation of the Charge Carrier Dynamics in Antimony Selenide Thin‐Film Solar Cells Based on the Effective Diffusion of Ions at the Heterojunction Interface

AbstractAntimony selenide (Sb2Se3) is regarded as a next‐generation material for high‐efficiency photovoltaic applications due to its favorable bandgap, high absorption coefficient, carrier mobility, and stability. Nonetheless, cadmiun sulfide (CdS) has low short‐wavelength transmittance, which limits photon utilization, and the suboptimal band alignment in the CdS/Sb2Se3 heterojunction causes significant interface recombination. In this study, a simple lithium‐ion doping method is presented and report the dual enhancement effects of lithium ions on CdS and Sb2Se3 layers for the first time. Lithium ions improve the CdS layer by allowing for larger grain sizes, reduces roughness, and increase transmittance in the electron transport layer. At the same time, lightweight Li ions diffuse more easily through the interface into the Sb2Se3 layer, resulting in improved orientation, lower defect density, and a longer carrier lifetime. Furthermore, doping with Li ions changes the band alignment of the CdS/Sb2Se3 junction from a “cliff‐like” to a “spike‐like” configuration, improving carrier transport and reducing carrier recombination near the interface. Ultimately, due to the benefits of Li‐ion doping, the champion device obtained have a VOC of 0.462 V, a JSC of 30.86 mA cm−2, an FF of 65.46%, and an efficiency of 9.33%, representing a 15.8% increase over the undoped device.

Atomic layer deposition of ultrathin nitride films for enhanced carrier lifetimes and photoluminescence in CdTe/MgCdTe double heterostructures

This work evaluates the passivation effectiveness of ultrathin nitride layers (SiNx, AlN, and TiN) deposited via atomic layer deposition on CdTe/MgCdTe double heterostructures for solar cell applications. Time-resolved photoluminescence and photoluminescence measurements revealed enhanced carrier lifetimes and reduced surface recombination, indicating improved passivation effectiveness. These results underscore the potential of SiNx as a promising passivation material to improve the efficiency of CdTe solar cells.

Efficient Blade-Coated Wide-Bandgap and Tandem Perovskite Solar Cells via a Three-Step Restraining Strategy.

Blade-coating techniques have attracted significant attention for perovskite solar cells (PSCs)due to their high precursor utilization and simplicity. However, the power conversion efficiency (PCE) of blade-coated PSCs often lags behind that of spin-coated devices, mainly due to difficulties in precisely controlling perovskite film formation during pre-nucleation, heterogeneous nucleation, and crystallization in the blade-coating and N2-knife drying processes. In this work, a three-step restraining strategy is introduced utilizing functional glycine amide hydrochloride to regulate pre-nucleation clustering, suppress excessive heterogeneous nucleation, and decelerate crystallization, enabling comprehensive control of the perovskite film formation processes. This approach results in enlarged grains, reduced defect densities, and highly oriented crystalline wide-bandgap perovskite films with significantly prolonged carrier lifetimes, achieving a maximum PCE of 19.97% for 1.77 eV-bandgap blade-coated PSCs. Furthermore, two-terminal tandem cells, composed of wide-bandgap perovskite top cells and 1.25 eV-bandgap perovskite bottom cells fabricated via blade coating, yield an impressive PCE of 27.11% (stabilized at 26.87%). This study offers comprehensive insights into controlling pre-nucleation, heterogeneous nucleation, and crystallization during blade coating, providing valuable guidance for developing high-performance, large-area devices in the future.

Construction and Multifunctional Photonic Applications of Light Absorption-Enhanced Silicon-Based Schottky Coupled Structures.

To expand the detection capabilities of silicon (Si)-based photodetector and address key scientific challenges such as low light absorption efficiency and short carrier lifetime in Si-based graphene photodetector. This work introduces a novel Si-based Schottky coupled structure by in situ growth of 3D-grapheneand molybdenum disulfide quantum dots (MoS2 QDs) on Si substrates using chemical vapor deposition (CVD) and plasma-enhanced chemical vapor deposition (PECVD) techniques. The findings validate the "dual-enhanced absorption" effect, enhancing the understanding of the mechanisms that improve optoelectronic performance. The synergistic effect of 3D-graphene's natural nano-resonant cavity and MoS2 QDs enhances light absorption efficiency and extends carrier lifetime. Introducing MoS2 QDs broadens and intensifies the built-in electric field, promoting the separation of photogenerated electrons and holes. The photodetector exhibits a wideband light response in the wavelength range of 380-2200nm. It stably outputs photocurrent under high-frequency (1 kHz) modulated laser (2200nm), with a responsivity (R) of 40mAW-1 and detectivity (D*) of 1.15×109 Jones. Photodetectors show the ability to process and encrypt complex binary signals and achieve versatility in "AND" gate and "OR" gate logic operations, as well as image sensing (240×200 pixels).

Engineering ZnIn2S4 Nanosheets with Zinc Vacancies: Unleashing Enhanced Photocatalytic Degradation of Tetracycline.

Defect engineering is a highly effective strategy for accelerating charge transfer and enhancing the performance of photocatalysts. In this study, ZnIn2S4 nanosheets were designed and prepared with controlled Zn vacancies to optimize the electronic band structure and localized charge density of ZnIn2S4. EPR results confirmed the formation of Zn vacancies. This modification enabled efficient capture of photoexcited charges in defect centers, thereby prolonging the carrier's lifetime. Theoretical calculations demonstrated that these vacancies induced the formation of new defect states and highly efficient surface reaction sites. As anticipated, under visible light irradiation, the photocatalytic tetracycline removal rate of the ZnIn2S4 nanosheets with Zn vacancies reached 82.8% within 60 min, significantly higher than that observed for the pristine ZnIn2S4 sample. These findings offer valuable insights into the deliberate construction of metal-vacancy-containing photocatalytic nanomaterials for the enhanced degradation of micropollutants.

Prolonging Charge Carrier Lifetime via Intraband Defect Levels in S-Scheme Heterojunctions for Artificial Photosynthesis.

S-scheme heterostructure photocatalysts, distinguished by unique charge-transfer pathways and exceptional catalytic redox capabilities, have found widespread applications in addressing challenging chemical processes, including the photocatalytic reduction of CO2 with a high reaction barrier. Nevertheless, the influence of intraband defect levels within S-scheme heterojunctions on charge separation, carrier lifetime, and surface catalytic reactions has, for the most part, been overlooked. Herein, we develop a tunable defect-level-assisted strategy to construct an electron reservoir, effectively prolonging the lifetime of charge carriers through the rapid capture and gradual release of photoelectrons within WO3-x/In2S3 S-scheme heterojunctions, as authenticated by femtosecond transient absorption spectroscopy and theoretical simulations. The surface photoredox mechanism, unraveled by Gibbs free energy calculations, demonstrates that oxygen-vacancy-induced defect states in WO3-x/In2S3 heterojunctions unlock the rate-determining H2O oxidation into free oxygen molecules by forming metastable oxygen intermediates, contributing to the facilitation of H2O photooxidation. This distinct role, combined with the extended carrier lifetime, results in boosted CO2 photoreduction with nearly 100 % CO selectivity in the absence of any photosensitizer or scavenger. Our work sheds light on the role of controllable defect levels in governing charge transfer dynamics within S-scheme heterojunctions, thereby inspiring the development of more advanced photocatalysts for artificial photosynthesis.

Prolonging Charge Carrier lifetime via Intraband Defect Levels in S‐scheme Heterojunctions for Artificial Photosynthesis

Prolonging Charge Carrier lifetime via Intraband Defect Levels in S‐scheme Heterojunctions for Artificial Photosynthesis

Polymer‐Assisted Nucleation for Stable Single‐Crystal Perovskite Thin Films

AbstractOrganic‐inorganic hybrid perovskite single crystals have emerged as a strong candidate in photovoltaic and general optoelectronic applications. However, the high supersaturation of the precursor solution leads to the rapid formation of a significant number of nuclei and a diminished concentration of perovskite solute. Consequently, the inadequate availability of precursors poses challenges in sustaining the subsequent crystal growth phase, culminating in the development of small‐sized single crystals. In this work, we report a controlled nucleation process to foster the growth of large‐size single crystals. This method through the coordination interaction between polyacrylic acid and Pb2+ ions, and substitution of the coordination with I− ions. This reduces the formation of the Pb‐I6 complex, which promptly emerges in a state of supersaturation and acts as a nucleus, thereby effectively reducing the number of nuclei formed. The single crystals produced using this method exhibit a lateral size exceeding 5 mm, an extended absorption range, a longer carrier lifetime of 10.93 ns, and enhanced stability. These crystals demonstrate the ability to remain stable even after storage in an ambient environment (T=20±5 °C, RH=60±5 %) for a period of 20 days.

Energy Band Alignment and Defect Synergistic Regulation Enable Air-Solution-Processed Kesterite Solar Cells With the Lowest VOC Deficit.

The major challenge in preparing high-performance Cu2ZnSn(S,Se)4 solar cells is the large open circuit voltage deficit (VOC-def). A new strategy utilizing the synergistic substitution of Ag and In dual cations has been proposed to simultaneously address the problems of undesirable interface band alignment and high-density detrimental bulk defects, obtaining decreased carrier recombination rate and increased minority carrier lifetime. The shorter In-S/Se bonds move the CBM higher by generating stronger repulsive force than the Sn-S/Se bonds, thus adjusting the interface band alignment. Ag substitution can effectively suppress Cu─Zn disorder, while Ag, In dual substitution can further passivate Sn-related defects and solve the issue of low carrier concentration in Ag single-substituted samples. Besides, the superior carrier property of In-Se materials significantly enhanced the device carrier lifetime and minority carrier diffusion length. The state-of-the-art air-solution-processed CZTSSe device without any addition treatment with 14.33% efficiency and 580mV VOC is obtained, possessing the lowest VOC-def value currently available in the CZTSSe field (VOC/VOC SQ = 64.7%). This work emphasizes the synergistic modulation of band alignment, defect level, grain growth, and carrier transportation by dual cation substitution, which paves a convenient and effective way to realize high-performance solar cells and photovoltaic devices.

Development and Performance of ZnO/MoS2 Gas Sensors for NO2 Monitoring and Protection in Library Environments

The presence of harmful oxidizing gases accelerates the oxidation of cellulose fibers in paper, resulting in reduced strength and fading ink. Therefore, the development of highly sensitive NO2 gas sensors for monitoring and protecting books holds significant practical value. In this manuscript, ZnO/MoS2 composites were synthesized using sodium molybdate and thiourea as raw materials through a hydrothermal method. The morphology and microstructure were characterized by X-ray diffraction analysis (XRD), energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The ZnO/MoS2 composite exhibited a flower-like structure, with ZnO nanoparticles uniformly attached to the surface of MoS2, demonstrating advantages such as high specific surface area and good uniformity. The gas sensitivity of the ZnO/MoS2 nanocomposites reached its peak at 260 °C, with a sensitivity value around 3.5, which represents an improvement compared to pure ZnO, while also enhancing sensitivity. The resistance of the ZnO/MoS2 gas sensor remained relatively stable in air, exhibiting short response times during transitions between air and NO2 environments while consistently returning to a stable state. In addition to increasing adsorption capacity and improving light utilization efficiency, the formation of hetero-junctions at the ZnO-MoS2 interface creates an internal electric field that effectively promotes the rapid separation of photo-generated charge carriers within ZnO, thereby extending carrier lifetime.

Enhancement of the quality of mc-Si ingot grown by vacuum directional solidification furnace with growth rate increase reducing the cost of the wafer for PV application: Carbon and oxygen analysis

In this paper, we propose a numerical model to investigate the dissolution of oxygen atoms from the porous silica crucible, SiO gas formation, back diffusion of CO gas and segregation of carbon and oxygen during the growth of multi-crystalline silicon (mc-Si) by vacuum directional solidification (VDS) at different growth rates (3, 6 and 9 mm/h) by silt valve opening rate. The dissolution of oxygen decreases during the rapid growth of ingot because the reaction between the molten silicon and the porous silica crucible is constrained. This limitation on oxygen dissolution from the porous silica crucible further diminishes chemical reaction inside the VDS furnace. Consequently, the segregation pattern of the carbon and oxygen is affected at higher growth rate. During the VDS mc-Si growth, a growth rate of 9mm/h yields better quality of the VDS grown mc-Si ingots compared to other growth rates, this rate reduces SiC precipitation and SiO2 cluster formation due to lower concentration of carbon and oxygen. The obtained carbon concentration minimizes the wire saw defects. Based on these numerical results (9 mm/h), we have implemented experimental work. Prepared samples are analyzed using FTIR spectra and minority carrier lifetime measurements. The effect of oxygen concentration in the samples is analyzed in the minority carrier lifetime measurements. The oxygen and carbon concentrations are calculated by FTIR spectra and their results are compared with the numerical simulation.

Mitigating Band Tailing in Kesterite Solar Absorbers: Ab Initio Quantum Dynamics.

Open-circuit voltage deficits are limiting factors in kesterite solar cells. Addressing this issue by suppressing band tailing and nonradiative charge recombination is essential for enhancing the performance. We employ ab initio nonadiabatic molecular dynamics to elucidate the origin of band tailing and charge losses and propose a mitigation strategy. The simulations show that Cu-Zn disorder, associated with antisite defect clusters [CuZn+ZnCu], is a significant source of band tailing in kesterites, as evidenced by the much larger Urbach energy in disordered than ordered kesterites. Cu-Zn disorder gives rise to new sulfur-centered coordination polyhedra, increases structural inhomogeneity, changes electrostatic potential at sulfur centers, and shifts the S(3p) orbital energy. Differences in the S(3p)/Cu(3d) and S(3p)/Sn(5s) hybridization strengths and the S(3p) orbital energy shift reduce the band gap by 0.37 eV. Furthermore, Cu-Zn disorder enhances vibrational motion of sulfur anions and surrounding cations, increasing band gap fluctuations by 15 meV. The stronger electron-phonon interactions reduce charge carrier lifetimes and limit the kesterite solar cell efficiency. Partial substitution of Zn with Cd facilitates structural ordering and significantly suppresses band tailing, particularly in disordered systems. The improvement can be attributed to the larger atomic radius and mass of Cd, which weakens bonding around the anion, suppresses S-related vibrations within the covalent tetrahedra, and reduces nonadiabatic coupling, thereby increasing charge carrier lifetimes. The reported results establish the key influence of cation disorder on band tailing and reduced charge carrier lifetimes in kesterites and highlight cation disorder engineering as a strategy to achieve high-efficiency kesterite solar cells.

Construction of 2D/2D Pd Metallene/COFs System with Strong Internal Electric Field for Outstanding Solar Energy Photocatalysis.

Due to the severe recombination of charge carriers, the photocatalytic activity of covalent organic frameworks (COFs) materials is limited. Herein, through simple ultrasound and stirring processes, the Pd metallene (Pde) is successfully combined with 2D COFs to form Pde/TpPa-1-COF (Pde/TPC) composites. Obviously, a strong internal electric field (IEF) is successfully formed in Pde/TPC hybrid materials, which significantly boosts the separation of photogenerated charges. In addition, the matched 2D structure of the two materials can also lead to electronic coupling effects, plentiful active sites, and shortened carrier migration paths. Thus, the Pde/TPC hybrid materials own extraordinary carrier separation ability with a longer carriers lifetime (3.3 ns for Pde/TPC and 2.7 ns for TPC), which can be proved series of photoelectrochemical and spectroscopic tests. Benefiting from the formation of IEF and the matched 2D structure, the 8% Pde/TPC demonstrates the highest photocatalytic H2 evolution efficiency, with H2 production rate reaching up to 5.85 mmolg-1h-1, which is over 25 times greater than that of pristine COFs, also exceeding that of many reported COFs-based photocatalysts. This research provides new perspectives and innovative approaches to further research on enhancing the internal electric field of COFs to promote their photocatalytic performance.

Preparation of Bi2CrO6/CuO heterostructure nanocomposite to increase methylene blue decomposition under visible light irradiation

In this study, the Bi2CrO6/CuO nanocomposite was used for the photocatalytic degradation of methylene blue (MB) under visible light. Nanocomposites with different ratios (1:1, 1:2, 2:1) were synthesized under hydrothermal conditions and investigated for MB removal. Various characterization techniques, including XRD, FT-IR, FE-SEM, BET, DRS, PL, and EDS, were employed to elucidate the physicochemical aspects of the catalysts. The 2:1 nanocomposite ratio was selected as the photocatalyst with the highest removal efficiency (85 %). Four main factors, including initial concentration, solution pH, catalyst dose, and light intensity, were studied using the response surface methodology (RSM) and the Box-Behnken model. Under optimal conditions, the MB removal efficiency reached 90.06 %. Additionally, the effect of oxidizing agents (H2O2) on the enhanced removal of MB was investigated. The improved photocatalytic performance of the Bi2CrO6/CuO (2:1) nanocomposite is attributed to visible light absorption, the formation of a p-n heterostructure, efficient charge separation via the S-scheme mechanism, and increased charge carrier lifetime. Moreover, economic calculations showed that the estimated costs for the photocatalytic removal of MB from wastewater are cost-effective.

Exploring Ultrafast Carrier Dynamics in Photoelectrochemical Water Splitting Using Transient Absorption Spectroscopy

AbstractHydrogen fuel produced from water splitting using sunlight remains one of the cleanest and most sustainable energy sources. However, photoelectrochemical hydrogen production faces several challenges, including poor sunlight absorption, deficient charge carrier lifetime and transfer rates, and very sluggish kinetics of the water oxidation half‐reaction. To address these challenges, researchers have concentrated on enhancing the efficiency of photoelectrochemical water splitting. A critical factor in this enhancement is a deeper understanding of the fundamental processes involved in photoabsorption and the subsequent oxidation evolution reaction. The advent of ultrafast lasers has enabled the detailed tracking of charge carriers within materials after sunlight absorption, including their separation and migration to the surface for water oxidation. Ultrafast transient absorption spectroscopy is a powerful technique that allows real‐time observation of the behavior of excited states and charge carriers on femtosecond to nanosecond timescales. Recent studies utilizing ultrafast transient absorption spectroscopy are explored to investigate the dynamics of charge carriers in photoelectrochemical water splitting, providing insights into the mechanisms that lead to the design of enhanced photoanodes with improved efficiency.

Electronic Coupling Between Perovskite Nanocrystal and Fullerene Modulates Hot Carrier Capture

AbstractThe efficient harnessing of hot carriers holds transformative potential for next‐generation optoelectronic devices. Halide perovskites, with their remarkably long carrier lifetimes exceeding 10 picoseconds, stand at the forefront of this research frontier. Yet, a fundamental paradox persists: why does efficient hot carrier capture remain elusive despite these extended lifetimes? Here, this conundrum is unraveled by constructing a donor–acceptor model system: perovskite nanocrystal and fullerene hybrids. It is demonstrated that the challenge lies not only in the carrier lifetime itself but in the nature of the coupling between donor and acceptor components. Remarkably, it is discovered that the formation of ground‐state complexes, with effective coupling across a wide energy range, not only overcomes the initially forbidden hot carrier capture within these hybrids but also dramatically enhances it, achieving a ≈76% hot carrier capture efficiency. This finding shifts the paradigm of hot carrier capture from extending carrier lifetimes to engineering donor–acceptor coupling, illuminating a path toward practical hot carrier applications.