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Conducting Polymers || Electrical Properties of Polymer Light-Emitting Devices
摘要： In this chapter, we present a brief introduction to semiconducting properties of conjugated polymers and the motivation to apply this class of materials in electronic/optoelectronic devices such as polymer light-emitting diodes (PLEDs). We describe, in detail, the operating mechanisms of PLEDs, with particular focus on the effects of charge injection and transport and their dependence on the external electric field and temperature. The mechanisms of current injection from the electrodes into the organic semiconductor are initially treated using traditional models for thermionic emission and tunnelling injection. More recent models considering the influence of metal/semiconductor interface recombination and of energetic and spatial disorder in the injection currents are also introduced and discussed. In addition, models considering space-charge-limited currents and trap-filling-limited currents are employed to describe the charge transport characteristics in the bulk. Furthermore, we present a brief discussion on ideas concerning the effects of the disorder on the charge-carrier transport behaviour.
关键词： space-charge-limited currents,conjugated polymers,polymer light-emitting diodes,organic semiconductors,electrical properties
更新于2025-09-19 17:15:36
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Pseudohalides in Lead-Based Perovskite Semiconductors
摘要： The emerging class of lead halide perovskite (LHP) semiconductors offers a surprising combination of low cost, ease of preparation, outstanding material properties, and performance in optoelectronic devices that has not yet been observed in any other class of material. Considering their general ABX3 formula, the halide (X) composition in LHP compositions has proven to be one of the best handles to control the material characteristics such as bandgap, morphology, and electronic properties. However, compared to the amount of effort that has been expended to discover new A cations and B cations, relatively few reports have dealt with the subject of discovering new X anions outside of the series of halides (Cl?, Br?, I?). In principal, a much wider range of anions with a ?1 charge (pseudohalides) may form the ABX3 stoichiometry with Pb2+, yet the general ability of polyatomic pseudohalides to form semiconducting perovskite crystal phases with Pb2+ remains an open question. Herein, the prospect of using polyatomic pseudohalide anions in LHP semiconductors is addressed.
关键词： light-emitting diodes,solar cells,halides,pseudohalides,perovskites
更新于2025-09-19 17:15:36
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The electron–hole overlap in the parabolic quantum well light emitting diode is much superior to the rectangular: even to that of a staggered quantum well
摘要： The strong piezoelectric field in the InxGa1?xN/GaN quantum well (QW) LEDs, separates the electrons and holes spatially, which decreases the luminescence. Various shapes and compositions of such QWs are studied to improve the performance. We have studied the transition energy (TE), overlap of electron and hole wave functions, band structures and field distributions of the parabolic QWs (PQW) through the self consistent solutions of Schr?dinger and Poisson equations. The shape of the PQW is varied along with the compositions and dopings. The square of the overlap of electron and hole wave functions i.e. the transition probability (TP) is strikingly increased, compared to the rectangular QW and it is even higher than the symmetrically staggered QW. At a particular current density, for the same TE, the TP of the PQW increases more than two times that of the rectangular QWs. An important feature, desirable for the QW LEDs emerge. The change of the TE with increase in the current density is minimized. A brief theory, computational procedures and the results will be presented in details with suitable discussions.
关键词： Light emitting diodes,J–V characteristics,Transition probability,Transition energy,InGaN/GaN parabolic QWs
更新于2025-09-19 17:15:36
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Ultrathin PEDOT:PSS Enables Colorful and Efficient Perovskite Light-Emitting Diodes
摘要： Recently, metal halide perovskite light-emitting diodes (Pero-LEDs) have achieved significant improvement in device performance, especially for external quantum efficiency (EQE). And EQE is mostly determined by internal quantum efficiency of the emitting material, charge injection balancing factor (ηc), and light extraction efficiency (LEE) of the device. Herein, an ultrathin poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (UT-PEDOT:PSS) hole transporter layer is prepared by a water stripping method, and the UT-PEDOT:PSS can enhance ηc and LEE simultaneously in Pero-LEDs, mostly due to the improved carrier mobility, more matched energy level alignment, and reduced photon loss. More importantly, the performance enhancement from UT-PEDOT:PSS is quite universal and applicable in different kinds of Pero-LEDs. As a result, the EQEs of Pero-LEDs based on 3D, quasi-3D, and quasi-2D perovskites obtain enhancements of 42%, 87%, and 111%, and the corresponding maximum EQE reaches 17.6%, 15.0%, and 6.8%, respectively.
关键词： poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate),perovskites light-emitting diodes,outcoupling efficiency,light-emitting diodes
更新于2025-09-19 17:13:59
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TE/TM mode full-spatial decomposition of AlGaN-based deep ultraviolet light-emitting diodes
摘要： The full-spatial decomposition of transverse electric (TE) / transverse magnetic (TM) mode in AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs) has been experimentally investigated, by introducing self-built light intensity test system mainly composed of angle resolution bracket, Glan-Taylor prism and spectrometer. By means of roughening the sapphire sidewall, the extraction efficiency of DUV-LED is improved, for both TE and TM mode light with no polarization selectivity. The introduction of self-built light intensity metrology system has been reflected via scribing the sapphire sidewalls using various laser conditions, which show a reliability in the enhancement validation of the light extraction efficiency. More importantly, the self-built light intensity test system enables effective feedback on epitaxial structures and chip structure design and provides a new perspective to design high efficiency AlGaN-based DUV-LEDs.
关键词： AlGaN,TE/TM mode light,sapphire sidewall roughening,deep ultraviolet light emitting diodes
更新于2025-09-19 17:13:59
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Rational design of colloidal core/shell quantum dots for optoelectronic applications
摘要： Colloidal core/shell quantum dots (QDs) are promising for solar technologies because of their excellent optoelectronic properties including tunable light absorption/emission spectra, high photoluminescence quantum yield (PLQY), suppressed Auger recombination, efficient charge separation/transfer and outstanding photo-, thermal-/chemical stability. In this review, engineered core/shell QDs with various types of band structures and corresponding device performance in luminescent solar concentrators (LSCs), light-emitting diodes (LEDs), solar-driven photoelectrochemical (PEC) devices and QDs-sensitized solar cells (QDSCs) are summarized. In particular, the applications of interfacial layer engineering and eco-friendly, heavy metal-free core/shell QDs in optoelectronic device are highlighted. Finally, strategies towards the developments and practical perspectives of core/shell QDs are briefly mentioned to offer guidelines for achieving prospective high-efficiency and long-term stable QD devices.
关键词： Core/shell quantum dots,Photoelectrochemical cells,Light-emitting diodes,Solar cells,Luminescent solar concentrators
更新于2025-09-19 17:13:59
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Organic-inorganic hybrid composites as an electron injection layer in highly efficient inverted green-emitting polymer LEDs
摘要： Organic-inorganic hybrid light emitting diodes (HyLEDs) consist of an organic emission layer in combination with at least one metal oxide charge injection layer in an inverted structure. Low temperature, solution processing of metal oxide charge injection layers is one of the key factors in reducing the manufacture cost of HyLEDs. Herein, we report the use of composite materials, comprising conjugated polyelectrolytes (CPE) and zinc oxide nanoparticles (ZnO NPs), as the electron injection layer (EIL) in highly-efficient, green-light-emitting poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) polymer LEDs that are carefully optimised for use in an inverted HyLED architecture for the first time. The composite CPE:ZnO EILs are processed via a room temperature, one-step, solution deposition and enable superior device performance relative to ZnO NPs on their own. We find that specifically, they (i) improve EIL morphology, reducing surface roughness as well as pin-hole size and density, (ii) induce a favourable vacuum level shift for electron injection by coordinate bonding between the CPE and ZnO constituents, and (iii) reduce interfacial quenching by passivation of ZnO chemical defects caused by oxygen vacancies. This work is also the first demonstration that blending ZnO NPs and CPE supports much faster electroluminescence turn-on times (~7.12 μs) than for traditional ZnO/CPE bilayer devices (~0.4 s) via ‘locking’ of the CPE mobile ions, as well as higher device performance. This demonstrates good suitability for display applications. After optimisation of the EIL composition and the thickness of the F8BT emissive layer, we achieve promising device efficiencies of 16.5 cd/A and 5.41 lm/W for devices with a 1.1 μm thick F8BT layer, which is particularly relevant for potential roll-to-roll fabrication. These results clearly demonstrate the potential that this organic-inorganic composite EIL material has for the realisation of cheap, scalable and highly efficient, printable HyLED devices.
关键词： inverted,Hybrid light-emitting diodes,nanoparticles,electron injection layers,conjugated polyelectrolytes,zinc oxide
更新于2025-09-19 17:13:59
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Novel Lewis Base Cyclam Self-Passivation of Perovskites without Anti-Solvent Process for Efficient Light-Emitting Diodes
摘要： Metal halide perovskites have been focused as a candidate applied as a promising luminescent material for next-generation high-quality lighting and high-definition display. However, as perovskite film formed, high density of defects would produce in solution processing inevitably, leading to low exciton recombination efficiency in light-emitting diodes (LEDs). Herein, a facile and novel self-passivation strategy to inhibit defects formation in perovskite film for constructing high performance LEDs is developed. For the first time, we introduce 1,4,8,11-tetraazacyclotetradecane (cyclam) in perovskite precursor solution and it spontaneously passivates defect states of CsPbBr3-based perovskite by coaction between amine and uncoordinated lead ions during spin-coating without anti-solvent process. Furthermore, as a delocalized system, cyclam also possesses chemical properties that facilitate exciton transportation. The proposed passivation strategy boosts the external quantum efficiency (EQE) from 1.25% (control device) to 16.24% (cyclam-passivated device). Further, defects passivation is also conductive to reduce LED degradation paths and improve device stability as the extrapolated lifetime (T50) of LEDs at an initial brightness of 100 cd/m2 is increased from 0.9 h to 127 h. These findings indicate the introduction of cyclam is highly effective to enhance the performance of LEDs, and such strategy in effectively reducing the defects could be also applied in other perovskite-based devices, such as lasers, solar cells, and photodetectors.
关键词： perovskites,self-passivation,light-emitting diodes,defect states,Lewis base cyclam
更新于2025-09-19 17:13:59
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Intrinsically p-type cuprous iodide semiconductor for hybrid light-emitting diodes
摘要： Cuprous halides, characterized by a direct wide band-gap and a good lattice matching with Si, is an intrinsic p-type I-VII compound semiconductor. It shows remarkable optoelectronic properties, including a large exciton binding energy at room temperature and a very small piezoelectric coefficient. The major obstacle to its application is the difficulty in growing a single-crystal epitaxial film of cuprous halides. We first demonstrate the single crystal epitaxy of high quality cuprous iodide (CuI) film grown on Si and sapphire substrates by molecular beam epitaxy. enhanced photoluminescence on the order of magnitude larger than that of GaN and continuous-wave optically pumped lasing were found in MBE grown CuI film. The intrinsic p-type characteristics of CuI were confirmed using an n-AlGaN/p-CuI junction that emits blue light. The discovery will provide an alternative way towards highly efficient optoelectronic devices compatible with both Si and III-nitride technologies.
关键词： molecular beam epitaxy,p-type semiconductor,light-emitting diodes,optoelectronic devices,cuprous iodide
更新于2025-09-19 17:13:59
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Small but powerful: Light-emitting diodes for inactivation of Aspergillus species in real water matrices
摘要： This study addressed the effectiveness of light emitting diodes to achieve inactivation of three different Aspergillus species (Aspergillus fumigatus, Aspergillus niger and Aspergillus terreus) in a real water matrix. Three single small ultraviolet-C diodes emitting light at two different wavelengths were tested: 255 nm that is similar to the wavelength emitted by low pressure mercury lamps and 265 nm that is closer to the maximum absorbance wavelength of DNA. The ultraviolet-C diodes emitting light at 265 nm were found to be more effective than the 255 nm, achieving 3-log, 1-log and 5-log inactivations of Aspergillus fumigatus, Aspergillus niger and Aspergillus terreus using less than 20 mJ/cm2 (13,97 mJ/cm2; 7,28 mJ/cm2; 19,74 mJ/cm2). The diodes have also affected the morphology of the fungal spores and increased the percentage of damaged and dead spores.
关键词： Aspergillus species,Membrane permeability,Enzymatic activity,Light emitting diodes,Spores morphology,Disinfection
更新于2025-09-19 17:13:59