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A “Positive Incentive” Approach to Enhance Operational Stability of Quantum Dot based Light-Emitting Diode
摘要： Balanced charge injection promises high efficiency of quantum dot based light-emitting diodes (QD-LEDs). Most widely used approach to realize charge injection balance is impeding the injection rate of the dominant charge carrier with energetic barriers. However, these approaches often accompany unwanted outcomes (e.g., the increase in operation voltage) that sacrifice the operation stability of devices. Herein, a “positive incentive” approach is proposed to enhance the efficiency and the operational stability of QD-LEDs. Specifically, the supply of hole, an inferior carrier than its counterpart, is facilitated by adopting a thin fullerene (C60) interlayer at the interface between hole injection layer (MoOX) and hole transport layer (CBP). The C60 interlayer boosts the hole current by eliminating the universal energy barrier, lowers the operation voltage of QD-LEDs, and enhances the charge balance in the QD emissive layer within working device. Consequently, QD-LEDs benefitting from the adoption of C60 interlayer exhibit significantly enhanced device efficiency and operation stability. Grounded on the quantitative assessment of the charge injection imbalance within the QD emissive layer, the impact of electrical parameters of QD-LEDs to their optoelectronic performance and operational stability is also discussed.
关键词： hole injection barrier,operational stability,fullerene,quantum dot based light-emitting diodes,charge injection balance
更新于2025-09-16 10:30:52
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Modulation of Ligands Conjugation for Efficient FAPbBr3 based Green Light-Emitting Diodes
摘要： Organic ligands capped on surface of perovskite nanocrystals (PeNCs) strongly influence the optical and electrical properties of the obtained PeNCs films, which are fundamental for efficient perovskite light-emitting diodes (PeLEDs). Here, we investigate the ligands effect through introduction of ligands with strong π conjugation, 1-(1-naphthyl)ethylamine bromide (NEABr), for the fabrication of FAPbBr3 PeNCs. Compared to the widely applied ligands of phenylethylamine bromide (PEABr), NEABr molecules containing naphthalene ring possess more delocalized electrons and better conductivity, which is beneficial for charge injection and transportation between interfaces. By varying the ligands ratio, high quality three dimensional FAPbBr3 PeNCs films with photoluminescence quantum yields up to 80% are fabricated. Based on the optimized PeNCs films, electroluminescent (EL) devices achieve a maximum external quantum efficiency of 8.6%, which is about three times higher than that of EL devices based on PEABr. Importantly, through understanding into the ligands effect, we demonstrate that the enhanced device efficiency is attributed to lower defect densities and decreased interfacial resistance in NEABr derived EL devices. Our findings about ligands conjugation on device performance may benefit other perovskites based optoelectronic devices.
关键词： ligands conjugation,perovskite nanocrystals,light-emitting diodes,charge injection,FAPbBr3
更新于2025-09-16 10:30:52
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Alkyl Group Wrapped Unsymmetrical Squaraine Dyes for Dye-sensitized Solar Cells: Branched Alkyl Chains Modulate the Aggregation of Dyes and Charge Recombination Processes
摘要： Electron transfer processes at the interfaces dictate the factors to improve the photovoltaic parameters such as open-circuit voltage (Voc) and short-circuit current (Jsc) of a dye-sensitized solar cell (DSSC) device besides selecting a set of suitable anode, dye, electrolyte and cathode materials. Inefficient charge injection process at dye-TiO2 interface and charge recombination at the TiO2-dye/electrolyte interface have detrimental effects in improving both Jsc and Voc. Hence tailoring the factors that governs to improve the Jsc and Voc will be an ideal approach to get the desired sensitizers with good device efficiencies. Squaraines are far-red active zwitterionic dyes, has high molar extinction coefficient along with unique aggregation properties due to the larger dipole moment associated with it. Here we report a series of unsymmetrical squaraine dyes, SQS1 to SQS6, with systematic variation of alkyl groups at sp3-C and N-atoms of indoline unit that was away from the anchoring group to control the dye-dye interactions on the TiO2 surface. The branched alkyl groups help to modulate the self-assembly of sensitizers on the TiO2 surface besides passivating the surface that helps to avoid the charge recombination processes. Light harvesting efficiency (LHE) and cyclic voltammetry studies of dye-sensitized TiO2 electrode indicated that the aggregation and charge hopping process between the dye molecules can be modulated, respectively by systematically increasing the number of carbon atoms in the alkyl groups. Such variation in the branched alkyl group helps to enhance the Voc from 672 (SQS1) to 718 mV (SQS6), Jsc from 7.95 (SQS1) to 12.22 mA/cm2 (SQS6), with the device efficiency ranging from 3.82% to 6.23% without any coadsorbent. Dye SQS4 has achieved highest efficiency of 7.1% (Voc = 715 mV, Jsc = 13.05 mA/cm2) with coadsorbent chenodeoxycholic acid (CDCA) using iodine (I-/I3 -) electrolyte compared to its analogs. Analysis of IPCE profile indicates that the major contribution of photocurrent generation is from the aggregated squaraine dyes on TiO2.
关键词： Un-symmetrical squaraines,charge recombination,charge injection,aggregation of dye,dye-sensitized solar cells
更新于2025-09-12 10:27:22
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Charge Injection from Excited Cs2AgBiBr6 Quantum Dots into Semiconductor Oxides
摘要： Lead-free double perovskites such as Cs2AgBiBr6 are gaining attention because of their environmental friendliness compared to the lead halide perovskites. In order to establish their photoactivity, we have probed the excited state behavior of Cs2AgBiBr6 nanocrystals and charge injection from their excited state into different metal oxides (TiO2, ZnO). The electron transfer rate constants determined from ultrafast transient absorption spectroscopy were in the range of 1.2–5.2 × 1010 s-1. Under steady state photolysis (ambient conditions) the electrons injected into TiO2 are scavenged by atmospheric oxygen, leaving behind holes which accumulate within the quantum dots (QDs). These accumulated holes further induce oxidation of QDs, resulting in the overall photodegradation of perovskite film. Annealed films of Cs2AgBiBr6 nanocrystals, when employed as an active layer in solar cell, delivered photocurrent under visible light excitation.
关键词： Metal oxides,Quantum dots,Photodegradation,Charge injection,Cs2AgBiBr6,Solar cells,Lead-free double perovskites
更新于2025-09-12 10:27:22
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Organic Photodetectors and their Application in Large Area and Flexible Image Sensors: The Role of Dark Current
摘要： Organic photodetectors (OPDs) have gained increasing interest as they offer cost-effective fabrication methods using low temperature processes, making them particularly attractive for large area image detectors on lightweight flexible plastic substrates. Moreover, their photophysical and optoelectronic properties can be tuned both at a material and device level. Visible-light OPDs are proposed for use in indirect-conversion X-ray detectors, fingerprint scanners, and intelligent surfaces for gesture recognition. Near-infrared OPDs find applications in biomedical imaging and optical communications. For most applications, minimizing the OPD dark current density (Jd) is crucial to improve important figures of merits such as the signal-to-noise ratio, the linear dynamic range, and the specific detectivity (D*). Here, a quantitative analysis of the intrinsic dark current processes shows that charge injection from the electrodes is the dominant contribution to Jd in OPDs. Jd reduction is typically addressed by fine-tuning the active layer energetics and stratification or by using charge blocking layers. Yet, most experimental Jd values are higher than the calculated intrinsic limit. Possible reasons for this deviation are discussed, including extrinsic defects in the photoactive layer and the presence of trap states. This provides the reader with guidelines to improve the OPD performances in view of imaging applications.
关键词： large area image sensors,charge injection,trap states,dark current,flexible image sensors,organic photodetectors
更新于2025-09-12 10:27:22
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Analytical modelling and parameters extraction of multilayered OLED
摘要： This research study investigates electrical performance of the multilayered organic light-emitting diode (OLED) with a focus on the role of charge injection, transport and emission layers. Device parameters; luminescence and current density are extracted using Silvaco ATLAS numerical device simulator and validated through the fabricated experimental results with a minor deviation of 3%. Furthermore, a mathematical model is applied to extract other device parameters such as electric field, charge carrier mobility, concentration and current density. Additionally, the multilayered device architecture is critically analysed through cut line methodology to better comprehend the internal device physics in terms of hole-electron mobility, concentration and their recombination. Subsequently, the performance parameters extracted using analytical model are compared with the results of internal analysis and a close match is observed. These results prove the Poole-Frenkel mobility-dependent behaviour in the OLEDs that varies following electric field. Analyses also highlight high electron and hole concentrations in the vicinity of the emission layer as a reason of high luminescence in the multilayered OLED, directly following the Langevin's theory of recombination in organic semiconductors. These analyses highlight the impact of different layers in the OLEDs and thus open up new horizons to further performance improvement in these devices.
关键词： Silvaco ATLAS,multilayered OLED,Poole-Frenkel mobility model,charge injection,Langevin's recombination model,transport and emission layers
更新于2025-09-12 10:27:22
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Exploring Electronic and Excitonic Processes Towards Efficient Deep Red CuInS2/ZnS Quantum-dot Light-emitting Diodes
摘要： The electroluminescence mechanisms in the Cd-free CuInS2/ZnS quantum-dot based light-emitting diodes (QLEDs) are systematically investigated through transient electroluminescence measurements. The results demonstrate that the characteristics of hole transporting layers (HTLs) determine the QLEDs to be activated by the direct charge-injection or the energy-transfer. Moreover, both the energy level alignment between HTL and quantum dot and the carrier mobility properties of the HTLs are critical factors to affect the device performance. By choosing suitable HTL, such as 4,4'-bis(9-carbazolyl)-2,2'-biphenyl, highly efficient deep red (emission peak at ~650 nm) CuInS2/ZnS QLEDs based on single HTL can be obtained with peak current efficiency and luminance of ~2.0 cd/A and nearby 3000 cd/m2, respectively.
关键词： energy transfer,charge injection,hole-transport layer,QLEDs,electron leakage,charge accumulation
更新于2025-09-11 14:15:04
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Study of charge injection in Ortho-, Meta- and Para-NKX-2553 in Dye-Sensitized Solar Cells: A theoretical approach
摘要： Dye sensitizers due to their significant role in the efficiency of Dye-Sensitized Solar Cells (DSSCs) have become the focal center of interest in recent years. In this study, NKX-2553 as one of the appealing metal-free organic dyes in different configurations of Ortho, Meta, and Para has been investigated. Parameters such as geometries, electronic structures, and optical properties, along with dipole moment, polarizability and first-order hyperpolarizability were calculated using density functional theory (DFT) and time-dependent DFT (TD-DFT). Results show that the Para-NKX-2553 is the best configuration in respect of increasing the charge injection in DSSCs. Moreover, according to our study, the efficiency of DSSCs can be improved through applying an external electric field in an appropriate direction.
关键词： Electric field,Charge injection,DFT,TD-DFT,Dye-sensitized solar cells,Electronic structure
更新于2025-09-11 14:15:04
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A simple and robust approach to reducing contact resistance in organic transistors
摘要： Efficient injection of charge carriers from the contacts into the semiconductor layer is crucial for achieving high-performance organic devices. The potential drop necessary to accomplish this process yields a resistance associated with the contacts, namely the contact resistance. A large contact resistance can limit the operation of devices and even lead to inaccuracies in the extraction of the device parameters. Here, we demonstrate a simple and efficient strategy for reducing the contact resistance in organic thin-film transistors by more than an order of magnitude by creating high work function domains at the surface of the injecting electrodes to promote channels of enhanced injection. We find that the method is effective for both organic small molecule and polymer semiconductors, where we achieved a contact resistance as low as 200 Ωcm and device charge carrier mobilities as high as 20 cm2V?1s?1, independent of the applied gate voltage.
关键词： contact resistance,organic transistors,charge injection,high work function domains,organic semiconductors
更新于2025-09-10 09:29:36
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Low-Voltage Operating Single-Wall Carbon Nanotube Thin-Film Transistors Using High Work Function Contacts on Flexible Substrates
摘要： There have been constant attempts as regards high-performance thin-film transistors (TFTs) by improving the charge injection between the source/drain electrode (S/D) and the channel. In this paper, we investigate the effect of the electric contact on the device performance of single-wall carbon nanotube (SWCNT) TFTs employing the suitable work function material. In order to realize the electric contacts for the dominant hole injection between the S/D and the SWCNT active channel, a high work function material of molybdenum trioxide (MoOx) fabricated by an optimized process are utilized. The contact resistance is extracted by plotting the width-normalized resistance of SWCNT-TFT with Pd and MoOx contacts as a function of channel length. We also demonstrate low-voltage operating SWCNT TFTs on flexible polyimide substrates with the reduced electric contacts. Without a buffer film which has been widely used to improve the device performance of TFT on a flexible substrate, high-performance low-voltage operating SWCNT-TFTs were achieved.
关键词： Flexible Substrate,Charge Injection,Device Performance,High Work Function Contacts,SWCNT TFTs
更新于2025-09-04 15:30:14