Trap States Research Articles

Antioxidant activity and in vitro fluorescence imaging application of N-, O- functionalized carbon dots.

Nanomaterials with dual-functions integrating diagnostic and therapeutic abilities have attracted the interest in biomedical applications, and low-dimensional carbon dots have shown their potentialities in the field owing to their versatile optical and physicochemical properties. Yet the link between the surface emissive states and their structure and composition is not well understood, and their stability and biocompatibility needs to be further investigated. We have prepared a series of N- and O-doped carbon dots from a commercial commodity with a high surface functionalization, and performed a deep analysis to rationalize the structure-performance indicators that control their fluorescence, cytotoxicity and antioxidant properties. The synthesized carbon dots exhibited broad multiple surface emissive states: a bright blue emission at 430nm governed by electronic transitions involving pyridones and carbonyl moieties, and a greenish emission at 500nm due to transitions involving C-N and C-O groups or trap states. The carbon dots displayed good photostability with negligible photobleaching over continuous excitation during 2h. The carbon dots also displayed good antioxidant activity correlated to the electron storage capacity of the aromatic core and O- and N- groups with proton exchange capacity. The carbon dots showed excellent cytotoxicity on human gingival fibroblast cell lines, and good response in in vitro fluorescence imaging over a wide concentrations range (0.05-1mg/mL), similar to other contrast agents, demonstrating the potential of these N-O- doped carbon dots in imaging applications.

Ultra‐High Switching Ratio Memtransistor Based on Van Der Waals Heterostructures Toward Neuromorphic Computing

The exceptional resistive switching characteristics and neuromorphic computational potential of memristors are crucial for advancing information processing in both traditional and non‐traditional computing paradigms. However, the non‐ideal resistive switching behavior of conventional oxide‐based memristors hardly meets the performance requirements for neuromorphic computing applications. Besides, the two‐terminal memristors are restricted by their configuration limitations toward multi‐field/multi‐functional modulation. Herein, this article presents a 2D GaSe/MoS2 heterojunction thin‐film transistor with four‐terminal (4‐T) tuning capability and flexible programming/erasing operations for non‐volatile storage. The heterojunction transistor demonstrates an exceptional resistance switching ratio exceeding 107, an ultra‐wide modulation range of 10–106, highly reliable stability, and cyclic durability. The in situ Kelvin probe force microscope and dynamic characterization reveal the conduction mediated by defect‐induced space charge limitations, as well as the tuning filling process of trap states within the channel by dual‐gate terminals. This device functions as a 4‐T artificial synapse, capable of achieving basic optoelectronic synaptic operations. The self‐denoising and pattern recognition capabilities exhibited by artificial neural networks based on this device serve as excellent examples for developing efficient and energy‐saving neuromorphic computing architectures.

Self-Assembled Monolayer-Mediated Crystallization Improvement and Energy Level Optimization in Inverted Perovskite Solar Cells.

The improved crystallization and precise energy level alignment achieved through self-assembled monolayers (SAMs) implementation constitute a critical technological advancement, facilitating inverted perovskite solar cells (PSCs) with simultaneously enhanced power conversion efficiency (PCE) and operational stability. Here, a benzocarbazole-derived SAM, BCPPA, is designed and synthesized as a hole-transporting layer (HTL) by fusing an additional benzene ring in one side of the carbazole core. In comparison to the commonly used carbazole-derived SAM of MeO-2PACz, BCPPA exhibits a larger molecular dipole moment, a deeper HOMO energy level, and a more hydrophobic character. These factors contribute to a favorable buried interface between the SAM and the perovskite, thereby leading to an optimal crystallization of perovskite films and an improved energy level alignment. Additionally, the BCPPA-based interface significantly reduces trap state density and suppresses nonradiative recombination. As a result, the BCPPA-based PSC achieves a champion PCE of 25.28% (certified at 25.01%), surpassing the MeO-2PACz-based device with a PCE of 24.44%. The unencapsulated BCPPA-based devices maintain 72% and 84% of their initial PCEs after aging at 85 °C for 600 h and tracking at maximum power point (MPP) for 512 h, respectively. The asymmetric SAM molecule is promising for fabricating highly efficient and stable inverted PSCs.

Defect Distribution in InAlGaN/GaN Structures with Different Passivation Schemes

This study presents the results of the deep level transient Fourier spectroscopy (DLTFS) study of the defect distribution in InAlGaN/GaN high electron mobility transistor layer structures with different passivation schemes. Two samples, one with SiNx + SiNx and one with Al2O3 + SiNx bilayers, are analyzed. The DLTFS spectra reveal only hole traps, with six identified in the SiNx + SiNx sample and three in the Al2O3 + SiNx sample. Traps with activation energy of 0.27 eV and 0.34 eV are attributed to Si‐related defects, while hole traps with activation energies of 0.88 eV, 0.92 eV, and 0.97 eV likely correspond to CN deep acceptor levels. The SiNx + SiNx sample exhibits a higher concentration, possibly linked to 2D hole gas formation under reverse bias. The choice of passivation layer affects the concentration of hole trap states assigned to the InAlGaN surface. These findings show that the Al2O3 + SiNx bilayer is particularly effective in defect mitigation, offering a good pathway for optimizing GaN electronics beyond conventional passivation approaches.

Bismuth-Doped Ag2Te Colloidal Quantum Dots for High-Performance Shortwave-Infrared Photodetectors.

Recently, silver telluride (Ag2Te) colloidal quantum dots (QDs) have garnered significant attention in short-wave-infrared (SWIR) photodetection owing to their strong SWIR responsivity and environmental benignity. However, the SWIR Ag2Te QDs often suffer from their high defect density, leading to an unsatisfactory utilization efficiency of the photogenerated charge carriers. To address this challenge, here, we have developed bismuth-doped Ag2Te (Bi:Ag2Te) QDs via a hot-injection doping method. The Bi doping effectively suppresses the trap states and modulates the energy band structure of the QDs. Then, the as-prepared Bi:Ag2Te QDs were applied in photodiodes, which exhibits outstanding detective performance in the SWIR range with high external quantum efficiencies of 11.2% and 30% under 0 and 0.3 V bias, respectively, and a specific detectivity (D*) of 7.67 × 1010 Jones at 1460 nm under ambient conditions. This study not only introduces novel QDs for high-performance SWIR photodetectors but also offers a critical reference for modulating the optoelectronic properties of QDs through doping strategies.

Multimode Long‐Persistent Luminescence and Photochromism From Lead‐Doped CsCdCl3 Metal Halide Toward Advanced Multiple Anti‐Counterfeiting and Information Storage

Abstract Doping in single‐component metal halide perovskites to adjust defect levels plays a crucial role in self‐trapped exciton (STE) emission, which is critical for tunable multi‐mode luminescence and photochromism (PC). The introduction of cations (Pb2+) into the hexagonal CsCdCl3 perovskite results in the disruption of the local symmetry of the matrix framework, establishing new trap states and trap centers, which in turn facilitate the creation of multimode persistent luminescence (PersL) materials. Temperature‐dependent fluorescence and thermoluminescence (TL) spectra reveal that Pb2+ influences the redistribution of defects, providing new emission pathways and enabling efficient tuning of the room‐temperature emission. In addition, chlorine vacancies (VCl) in CsCdCl3:Pb facilitates the capture of electrons to form F‐centers, resulting in remarkable PC. First‐principles theory simulations demonstrate the introduction of Pb2+ ions alter the original energy band structure and charge distribution, confirming their tendency to induce defect formation at different symmetry sites. This effective method of modifying the optical properties of CsCdCl3 microcrystals through Pb2+ doping integrates multimode tunable UV/X‐ray induced PersL and rewritable PC, offering promising material candidates for more reliable and efficient anti‐counterfeiting and information storage applications.

Pseudohalide BF4- Doping Suppresses Lattice Anharmonicity and Passivates the Pb-Pb Dimer in Defective CH3NH3PbI3 Perovskites.

Excess electron-induced Pb-Pb dimer formation critically degrades perovskite solar cell performance by converting shallow defects into deep trap states and generating highly localized small polarons that accelerate nonradiative recombination. Using density functional theory and nonadiabatic molecular dynamics, we demonstrate that pseudohalide BF4- doping can passivate such degradation by stabilizing the PbX6 octahedral framework and maintaining delocalized electrons without small polaron formation. This structural stabilization reduces lattice anharmonicity and atomic thermal fluctuations, while enhanced rigidity prevents the large atomic displacements required for dimer formation. The BF4- doping further weakens electron-vibration interaction and decreases nonadiabatic coupling strength, synergistically extending the carrier lifetime by approximately 6 times. Our findings establish pseudohalide doping as an effective strategy to inhibit excess electron-induced degradation through anharmonicity suppression, providing a broadly applicable approach for enhancing perovskite stability.

Curtailing Non-Radiative Recombination and Tailoring Interfacial Energetics via Bimolecular Passivation toward Efficient Inverted Perovskite Solar Cells.

Despite significant development of perovskite solar cells (PSCs) in recent years, presence of nonradiative recombination centers at the perovskite surface, grain boundaries, and interfaces remain a major bottleneck in achieving the desired device performance. Also, energy levels offset among perovskite and neighboring functional layers leads to poor charge extraction, thereby further limiting the device capability. Therefore, it is essential to carefully understand the underlying defects and develop a suitable passivation technique to suppress such detrimental imperfections. Herein, we propose a synergistic bimolecular passivation strategy to simultaneously reduce the trap states density, enhance crystallinity and improve interfacial charge transfer in inverted (p-i-n) PSCs. The poly(2-ethyl-2-oxazoline) (PEOXA) introduced in the antisolvent modulates the crystallization kinetics and concurrently passivates the grain boundaries and surface defects of perovskite films. In addition, a simple surface post-treatment of the perovskite layer using 3-(aminomethyl)pyridine (3-APy) suppresses contact-induced interfacial recombination as a consequence of lowered work function in the surface region. This synergistic passivation approach renders enhanced defect passivation and improved interfacial energetics, leading to a significant suppression in undesirable nonradiative recombinations and improvement of interfacial charge transfer. Consequently, the power conversion efficiency (PCE) of the devices significantly improves from 22.01 to 24.65% (with a certified PCE of 24.01%), while the operational stability at the maximum power point is maintained at a decent value for over 1000 h of continuous illumination. This work provides a guideline for developing multimolecular passivation approaches to selectively target various defects toward improved performance of perovskite optoelectronic devices.

HgTe Nanocrystal-Gated Infrared Phototransistors With High Sensitivity, Extended Dynamic Range, and In-Sensor Image Processing Capability.

Mercury telluride (HgTe) nanocrystals (NCs) offer adjustable absorption and solution-processable fabrication, making them promising materials for low-cost, high-resolution imaging across a wide infrared (IR) spectrum. However, photodetectors based on HgTe NCs often suffer from high dark current, elevated noise arising from trap states and interface defects, and limited structural tunability, which constrain their sensitivity, dynamic range, and applicability in intelligent vision applications. Here, it is reported a dual-gate carbon nanotubes (CNTs) field-effect transistor incorporating an HgTe NC-based PIN heterojunction as the top gate, which converts incident IR light into a photovoltage that functions as a dynamic optical gate, while an independently addressable local bottom gate adjusts the carrier concentration in the CNT channel. This opto-electrically decoupled yet synergistic architecture enables high responsivity (>103 A/W), excellent room-temperature specific detectivity (1013 Jones) under low-power IR illumination, and a wide dynamic range of 170dB to 1650nm infrared irradiation when biased in the subthreshold region. Furthermore, by leveraging gate-controllable and self-adaptive photoresponse, it is demonstrated in-sensor convolutional processing and image fusion at the device level. This dual-gate architectureprovides a new pathway toward high-performance IR photodetectors with in-sensor computing capabilities, advancing their potential for next-generation machine vision systems.

Structural and Optical Properties of a 0D Lead Iodide Hybrid Perovskitoid with Aromatic Diammonium Cations

0D hybrid organic–inorganic perovskitoids (HOIPs) are promising candidates for optoelectronic applications, due to the properties arising from the isolation of the metal halide octahedra, such as broadband photoluminescence (PL) emission, ambient stability, and reduced ion migration. However, a better understanding of the role of the organic cation in the crystal phase formed and resulting optical properties is needed, particularly regarding the appearance of anisotropy in the arrangement of the octahedra in the lattice. Here, the synthesis, crystal structure, and optical, vibrational, and electrical properties of a new 0D lead iodide HOIP containing 3‐(aminomethyl)pyridinium, 3AMPy, as organic cation, are presented. X‐ray diffraction reveals that 3AMPy2PbI6 has an orthorhombic crystal structure consisting of isolated [PbI6]4− octahedra. Polarization‐dependent Raman spectroscopy and optical microscopy reveal narrow modes with preferential crystal orientation and birefringence, respectively. 3AMPy2PbI6 exhibits an isotropic red broadband PL emission shifted to longer wavelengths compared to the 2D and 3D AMPy‐PbI2 phases and to other 0D Pb‐based HOIPs, which is ascribed to exciton recombination and trap states in the octahedra. Devices made with flakes of 3AMPy2PbI6 show photoconduction under 405 nm light. Our results provide insight into the structure and optical properties of 0D HOIPs and their potential in optoelectronic devices.

Interface trap states induced underestimation of Schottky barrier height in metal-MX2 junctions

Understanding the interfaces between a contact metal and a two-dimensional (2D) semiconductor, as well as the dielectric gate stack and the same 2D material in transition metal dichalcogenide (TMD) based transistors, is a crucial step towards the introduction of TMD materials into advanced logic nodes. In particular, for the contact metal/2D interface, one of the key parameters is the Schottky barrier height (SBH), which is frequently extracted based on temperature-dependent subthreshold characteristics of TMD field-effect transistors (FETs). However, recently, using this methodology has resulted in rather low extracted SBH values for TMD-based transistors, which seems inconsistent with the low on-current levels in said devices. Here, we therefore connect measured device characteristics on monolayer (ML) MoS2 transistors with technology computer-aided design (TCAD) simulations. In particular, our analysis shows that low SBHs can be incorrectly extracted when the interface trap density Dit is substantial and exhibits, at the same time, a significant temperature dependence, as is the case for TMDs. In fact, TCAD simulations and comparison with the obtained electrical data reveal that the actual SBH is substantially larger than what is extracted when ignoring the above mentioned details of Dit.

Plasmon-mediated dual S-scheme charge transfer in Cu2-xS/In2S3/Bi2S3 hollow polyhedrons for efficient Photothermal-Assisted photocatalysis.

Plasmon-mediated dual S-scheme charge transfer in Cu2-xS/In2S3/Bi2S3 hollow polyhedrons for efficient Photothermal-Assisted photocatalysis.

Indole-2-Carboxylic Acid Ligand-Mediated Synthesis of Stable Perovskite Nanocrystals for Fast Responsive Photodetector.

Cesium lead bromide perovskite nanocrystals (NCs) show great potential for photoelectric properties. However, due to their poor stability and the insulating nature of passivating ligands, they suffer from practical applications. Herein, in an approach to passivate NCs surface by introducing a ligand, Indole-2-carboxylic acid (ICA), we synthesized a mixed CsPbBr3/Cs4PbBr6 NCs by ligand-assisted re-precipitation approach. Incorporating ICA ligand in place of long chain insulating Oleic acid (OA) effectively reduced the loss of non-radiative recombination induced by surface trap states. Through all the performed compositional and structural characterization, the existence of CsPbBr3/Cs4PbBr6 mixed NCs was confirmed. The obtained CsPbBr3/Cs4PbBr6 mixed NCs show green emission at 518 nm and superior stability under ambient conditions compared to CsPbBr3 NCs. The photoluminescence (PL) of the CsPbBr3/Cs4PbBr6 mixed NCs increased approximately three times, and the photoluminescence quantum yield (PLQY) increased from 75 ± 2% to 94 ± 2% as compared to CsPbBr3 NCs.

Trap‐State Suppression via Dual Defect Healing Enables Stable Near‐Infrared Lanthanide‐Based Quantum Dot LEDs

Abstract Lanthanide‐alloyed perovskite quantum dots (QDs, Yb3+: CsPb(Cl1‐xBrx)3) are promising in near‐infrared light‐emitting diodes (NIR‐LEDs) for theoretically ≈200% photoluminance quantum yield because of quantum‐cutting effect, where one high‐energy photon is used as a source to generate two low‐energy photons. However, the inferior stability of Yb3+: CsPb(Cl1‐xBrx)3 remains a big challenge. It is posited that vacancy‐defect complexes during lanthanide ions alloying are the driving force behind the collapse of octahedral geometry. Here, a coordination agent compensation plus an in situ doping strategy is developed to address the incompatibility between high NIR emission and good stability. This is achieved by combining the sodium ion to fill the vacancy and a coordinating agent (pyridine‐2‐carboxylic acid) for passivation. This enabled the treated QD films to have a magnitude of order decreased deep trap density compared to the control. Besides, the treated composite exhibits a sixfold increase in NIR intensity and tenfold lower trap states. Using the optimized Yb3⁺: CsPb(Cl1‐xBrx)3, NIR‐LEDs are fabricated and achieved an external quantum efficiency of 8.2%, one of the highest values among NIR LEDs with emission >950 nm. Furthermore, these LEDs exhibit a 30‐fold increase in operational stability compared to the control.

Weak Electrostatic Network Structure Improves PbS Quantum Dot Ink Stability.

PbS quantum dot (QD) ink stability in polar solvents is critical for high-performance solar cell fabrication. However, QD aggregation in such solvents often leads to epitaxial fusion, resulting in trap states that degrade the device performance. Here, we demonstrate a novel strategy for enhancing ink stability by constructing a weak electrostatic network structure on the QD surface, which is cobuilt by hydrogen bonds and π interactions, providing a stable environment that prevents QD aggregation and epitaxial fusion. The optimized surface structure confers an ink film, with a 13% reduction in Urbach energy, a 50% decrease in trap state density, and a 107% prolongation of carrier lifetime, suggesting significantly enhanced carrier transport and extraction capabilities. With this approach, PbS QD solar cells can achieve a power conversion efficiency of 13% and remain stable for over 1000 h without encapsulation when stored in air.

Spontaneously Formed PbS Colloidal Quantum Dot Microstructures Make for High‐Performance Top‐Illuminated Short‐Wave Infrared Imager

A high‐performance top‐illuminated short‐wave infrared (SWIR) imager is achieved based on the solution‐processed PbS colloidal quantum dot (CQD) photodiodes, by introducing the spontaneously formed PbS microstructures on the active layer through managing the CQD packing manner simply by appropriate solvent selection. The presence of the PbS microstructures simultaneously serves the following two vital functions. The first is to exert the light trapping effect for higher photon absorption, as well as decrease trap states for inhibiting the trap‐assisted recombination of photogenerated carriers, both promoting the photoresponsivity in the SWIR region. The second is to remove surface cracks on the CQD films for reducing the defect‐induced current leakage paths, as well as reducing the trap‐assisted tunneling current, thereby suppressing reverse bias dark current density (Jdark). The top‐illuminated PbS CQD photodiodes reach a high photoresponsivity of 0.38 A W−1 at 1413 nm and a low Jdark of 8.2 ×10−8 A cm−2 at –1 V, which is among the best photodetection performances reported for top‐illuminated CQD SWIR photodiodes. Such SWIR photodiodes are integrated with the thin‐film transistors to produce a top‐illuminated imager with 64 × 64 pixels, which demonstrates excellent SWIR imaging performance. This work opens up an intriguing shortcut toward low‐cost, low‐noise, and high‐sensitivity SWIR imaging.

Modulation of SnO2 Electron‐Transporting Materials in Perovskite Solar Cells

Tin oxide (SnO2) is a commonly used electron‐transporting material (ETM) in perovskite solar cells (PSCs) due to its low‐temperature processability and suitable energy levels. However, its inherent limitations, such as insufficient electron mobility and high density of trap states, hinder further improvement of device performance. This review explores recent advances in modifying SnO2 ETMs to address these limitations and improve the efficiency and stability of n‐i‐p PSCs. We delve into the role of various dopants and surface modification strategies in enhancing electron transport properties and reducing the trap states. By elucidating the impacts of dopant chemical/electronic structures and surface treatments on SnO2 properties, this review provides valuable insights for the development of efficient ETMs for high‐performance PSCs.

Tailoring carrier management through a multifunctional additive for efficient perovskite/organic tandem solar cells

The wide bandgap perovskite solar cells (PSCs) are promising candidates for high-efficiency tandem photovoltaics. However, these devices encounter challenges arising from defects within the perovskite lattice and at interfaces, which lead to non-radiative recombination and voltage losses. To address these issues, we have developed a synergistic approach that combines bulk passivation using l-cystine dihydrochloride as an additive with subsequent surface passivation treatments. This compound effectively passivates Pb2+ and halide defects through its carbonyl and amine functional groups. Both experimental and simulation results demonstrate that l-cystine dihydrochloride effectively reduces trap states, retards nucleation kinetics, promotes grain growth, and enhances crystallinity. Consequently, the device [FA0.8Cs0.2Pb(I0.6Br0.4)3, energy gap: 1.77 eV] incorporating l-cystine dihydrochloride achieved a power conversion efficiency (PCE) of approximately 16.00%, which was further increased to 17.03% with an additional octylammonium iodide surface passivation. Expanding our approach, we have fabricated the wide bandgap semitransparent device, yielding a PCE of 15.62%. When integrated with narrow-bandgap organic solar cells in four-terminal (4T) perovskite/organic tandem solar cells, a remarkable efficiency of 23.14% was attained. This strategy effectively improves the performance of wide bandgap PSCs, which exhibit great potential in advancing perovskite/organic photovoltaic technologies.

Hole Injection Barrier‐Driven Positive Aging Mechanism in Inverted QLEDs

Abstract Positive aging is usually observed during the operation of quantum dot‐light‐emitting diodes (QLEDs), which introduces significant challenges for accurate performance assessment and industrial standardization. However, the mechanism of positive aging remains unclear and has long been attributed to the instability of the ZnO‐based electron transport layer. Here, a new operational positive aging mechanism in inverted‐structure QLEDs is reported, primarily driven by trap states at the interface of the hole transport layer (HTL). An elevated hole injection barrier can promote the accumulation of holes and their trapping via defect states, resulting in subsequent non‐radiative recombination. Operational aging induces a progressive reduction in defect‐mediated charge trapping, leading to a marked enhancement in radiative recombination efficiency and the device manifests as positive aging. By employing an insulating layer to spatially isolate the interface between quantum dots and HTL, the non‐radiative recombination of electrons and accumulated holes can be effectively mitigated. Consequently, the positive aging phenomenon is significantly suppressed, and the current efficiency of the fresh device is improved by 240%. These findings elucidate the critical effects of interface properties on carrier dynamics and provide a strategy for achieving optimal device efficiency at the early stage of operation.

Unveiling the Effects of Hydroxyl-Induced Trap States on the Charge Transport in p- and n-Channel Organic Field-Effect Transistors through Variable-Temperature Characterization.

Trap states at the gate dielectric-organic semiconductor (OSC) interface are one of the main sources of extrinsic traps in organic field-effect transistors (OFETs). However, they are often overlooked and their effects on the charge transport are attributed to the exposure of devices to ambient air. Here a first variable-temperature transfer length method characterization of both p- and n-channel OFETs under full high vacuum conditions is reported. By comparing a hydroxylated aluminum oxide (Al2O3) gate dielectric with a hydroxyl-free, tetradecylphosphonic acid-functionalized Al2O3 dielectric, it is shown that hydroxyl-induced trap states reduce the charge carrier mobility in OFETs regardless of the channel type. This observation challenges the common belief that the hydroxyl-induced traps are affecting primarily the n-channel transport. The variable-temperature analysis yields a high activation energy of charge transport as the main effect of a hydroxylated gate dielectric. Moreover, the injection barrier at the interface between the source-drain electrodes and the OSC layer is significantly lower for devices with a hydroxyl-free dielectric and correlates with the activation energy of charge transport. This work identifies previously hidden limitations of charge transport in OFETs, opening opportunities for further improvements in device performance and potential deviceapplications.