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Increased radiative recombination of AlGaN-based deep ultraviolet laser diodes with convex quantum wells
摘要： An AlGaN-based deep ultraviolet laser diode with convex quantum wells structure is proposed. The advantage of using a convex quantum wells structure is that the radiation recombination is significantly improved. The improvement is attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes, which results in an increased hole injection efficiency and a decreased electron leakage into the p-type region. Particularly, comparisons with the convex quantum barriers structure and the reference structure show that the convex quantum wells structure has the best performance in all respects.
关键词： AlGaN,radiation recombination,convex quantum wells,electron leakage,deep ultraviolet laser diode,hole injection efficiency
更新于2025-09-23 15:19:57
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Thickness-dependent hole-blocking capability of RF-sputtered nickel oxide compact layers in dye-sensitized solar cells
摘要： Photo-generated charge carrier recombination in dye-sensitized solar cells (DSSCs) is observed to be suppressed significantly at the interface between transparent fluorine-doped tin oxide (FTO) and titanium dioxide (TiO2) by coating nickel oxide (NiO) thin film by RF sputtering. UV-Visible optical absorption spectroscopic measurements performed in the wavelength window of 300–800 nm showed ~ 60% average transmittance for NiO thin films coated for 10 min. The calculated optical bandgap value for NiO was 3.4 eV. The RF-sputtered NiO films were thoroughly characterized by X-ray photo-electron spectroscopy to examine Ni 2p3/2 and Ni 2p1/2 along with O 1s. The present study assessed the effect of 5, 10, and 15 min RF-sputtered NiO thin films at the interface between FTO and mesoporous TiO2. Results showed that charge transport in DSSCs is highly sensitive to NiO thickness at the interface between FTO and TiO2. It was specifically noticed that 10 min coating of NiO on FTO yielded DSSCs with photo-conversion efficiency (η) of ~ 6.8% while DSSCs with no NiO on FTO showed only 4.9%. Further increase in NiO thickness affected the performance of DSSCs due to the significant reduction in tunneling probability from TiO2 to FTO.
关键词： Interfaces,Recombination,Nickel oxide,Charge transport,Dye-sensitized solar cells
更新于2025-09-23 15:19:57
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Direct-indirect GeSn band structure formation by laser Radiation: The enhancement of Sn solubility in Ge
摘要： Low equilibrium solid solubility of Sn atoms in Ge (less than 1%) leads to limitations in application of this material for IR detectors and emitters. Providing of non-equilibrium conditions by powerful pulsed laser radiation can be successfully applied for enhancement of solubility of impurity atoms in the host material. Here we present laser-induced monotonous redistribution of Sn atoms in Ge, based on the thermogradient effect aiming overcoming equilibrium limitations in the solubility. We applied pulsed nanosecond laser radiation to epitaxial Ge0.96Sn0.04 layer grown on Si substrate to increase Sn atomic concentration up to 14% at the surface layer. As a result, indirect-direct graded bandgap GeSn structure was formed. The TEM/EDS cross-section analysis, X-ray photoelectron spectroscopy, Raman and UV reflection spectra confirmed the increase of Sn atomic content at the surface by order of magnitude. SEM and AFM imaging provided evident microstructure changes, while carrier lifetime changes, determined by differential transmittivity, were not observed, indicating that laser irradiation does not generate defects which reduce electronic quality of the material.
关键词： Laser radiation,Thermogradient effect,Solid solution,Carrier recombination,GeSn
更新于2025-09-23 15:19:57
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Spin-Controlled Charge Recombination Pathways across the Inorganic/Organic Interface
摘要： Charge transfer and recombination across the inorganic/organic interface in nanocrystal or quantum dot (QD)-molecule hybrid materials has been extensively studied. Principles of controlling charge transfer and recombination via energetics and electronic coupling have been established. However, the use of electron spin to control transfer and recombination pathways in such systems remains relatively underexplored. Here we use CdS QD-alizarin (AZ) as a model system to demonstrate this principle. Using time-resolved spectroscopy, we found that the charge separated states (QD--AZ+) created by selectively exciting AZ molecules mostly recombined to regenerate ground state complexes, whereas the apparently “same” charge separated states created by exciting QDs recombined to produce AZ molecular triplet states. Such a difference can be traced to the distinct spin configurations between excited QDs (QD*, with an ill-defined spin) and AZ (1AZ*, spin singlet) and the asymmetric electron and hole spin-flip rates in II-VI group QDs. The transferability of such a principle was confirmed by similar observations obtained for CdS QD-tetracene complexes. Opening an avenue of controlling charge transfer and recombination pathways via electron spin is potentially important for applications such as artificial photosynthesis.
关键词： CdS QD-alizarin,artificial photosynthesis,quantum dot,inorganic/organic interface,triplet states,electron spin,recombination,time-resolved spectroscopy,Charge transfer
更新于2025-09-23 15:19:57
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Reversible intermolecular-coupled-intramolecular (RICI) proton transfer occurring on the reaction-radius <i>a</i> of 2-naphthol-6,8-disulfonate photoacid
摘要： Steady-state and time-resolved fluorescence techniques were employed to study the excited-state proton transfer (ESPT) from a reversibly dissociating photoacid, 2-naphthol-6,8-disulfonate (2N68DS). The reaction was carried out in water and in acetonitrile–water solutions. We find by carefully analyzing the geminate recombination dynamics of the photobase–proton pair that follows the ESPT reaction that there are ? side group at the 8 position which two targets for the proton back-recombination reaction: the original O? dissociation site and the SO3 is closest to the proton OH dissociation site. This observation is corroborated in acetonitrile-water mixtures of χwater < 0.14, where a slow ? group via H-bonding water. The proton-transferred R?O? fluorescence band in mixtures of χwater < 0.14 where only intramolecular ESPT occurs is red shifted by about 2000 cm?1 from the free R?O? band in neat water. As the water content in the mixture increases above χwater = 0.14, the R?O? fluorescence band shifts noticeably to the blue region. For χwater > 0.23 the band resembles the free anion band observed in pure water. Concomitantly, the ESPT rate increases when χwater increases because the intermolecular ESPT to the solvent (bulk water) gradually prevails over the much slower intramolecular via the water-bridges ESPT process.
关键词： 2-naphthol-6,8-disulfonate,photoacid,intermolecular ESPT,geminate recombination,intramolecular ESPT,excited-state proton transfer
更新于2025-09-23 15:19:57
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Amphoteric imidazole doping induced large-grained perovskite with reduced defect density for high performance inverted solar cells
摘要： Intrinsic defect density in polycrystalline halide perovskite films are required to be low enough to suppress charge recombination loss for improvement in performance of perovskite solar cells (PeSCs). In this paper, we propose the use of amphoteric imidazole to achieve high crystalline quality of CH3NH3PbI3 perovskite absorption layer. The imidazole additive plays a synergistic role in controlling the perovskite crystal growth for large grain size and passivating the uncoordinated ions (e.g., Pb2+) defects, resulting in improved carrier transport/lifetime and suppressed non-radiative recombination. The champion power conversion efficiency (PCE) of PeSCs with imidazole is improved to 16.88%, from the control device with a PCE value of 14.65%. Besides, the stability of imidazole modified perovskite films is further improved by limiting ion immigration at grain boundaries against moisture and heat stresses. The findings pave an avenue for synergistically modulating crystallization and healing defect in perovskite to achieve efficient and stable solar cells.
关键词： Defect passivation,CH3NH3PbI3,Grain boundary,Inverted solar cell,Non-radiative recombination
更新于2025-09-23 15:19:57
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Cesium Lead Bromide Quantum Dot Light-Emitting Field-Effect Transistors
摘要： Solution processible perovskite quantum dots are considered as promising optical materials for light emitting optoelectronics. The light-emitting field-effect transistors that can be operated under relatively lower potential with an efficient energy conversion efficiency have yet to be realized with the perovskite quantum dot. Here, we present the CsPbBr3 quantum dot-based light-emitting field-effect transistor (LEFET). Surprisingly, unipolar transport characteristics with strong electroluminescence was observed at the interface of the CsPbBr3 QD-LEFET along with the exceptionally wide recombination zone of 80 μm, an order of magnitude larger than that of organic/polymer light-emitting field-effect transistors. Based on the systematic analysis for the electroluminescence of the CsPbBr3 NC-LEFET, we revealed that the increased diffusion length determined by the majority carrier mobility and the lifetime well explains the remarkably wide recombination zone. Furthermore, it was found that the energy-level matching and transport geometry of the hetero-structure also determine the charge distribution and recombination, substantially affecting the performance of the CsPbBr3 QD LEFET.
关键词： Organic/inorganic hybrid field-effect-transistor,Light emitting field-effect-transistor,Wide recombination zone,Diffusion length,CsPbBr3 quantum dots
更新于2025-09-23 15:19:57
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Delocalization boosts charge separation in organic solar cells
摘要： Organic solar cells (OSCs) utilizing π-conjugated polymers have attracted widespread interest over the past three decades because of their potential advantages, including low weight, thin film flexibility, and low-cost manufacturing. However, their power conversion efficiency (PCE) has been far below that of inorganic analogs. Geminate recombination of charge transfer excitons is a major loss process in OSCs. This paper reviews our recent progress in using transient absorption spectroscopy to understand geminate recombination in bulk heterojunction OSCs, including the impact of polymer crystallinity on charge generation and dissociation mechanisms in nonfullerene acceptor-based OSCs. The first example of a high PCE with a small photon energy loss is also presented. The importance of delocalization of the charge wave function to suppress geminate recombination is highlighted by this focus review.
关键词： Polymer crystallinity,Power conversion efficiency,Organic solar cells,Transient absorption spectroscopy,Dissociation mechanisms,Photon energy loss,π-conjugated polymers,Charge generation,Nonfullerene acceptor,Geminate recombination
更新于2025-09-23 15:19:57
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Phenanthrenea??Fuseda??Quinoxaline as Key Building Block for Highly Efficient and Stable Sensitizers in Copper Electrolyte Based Dyea??Sensitized Solar Cells
摘要： Dye-sensitized solar cells (DSSCs) based on Cu(II/I) bipyridyl or phenanthroline complexes as redox shuttles have achieved very high open-circuit voltages (VOC, > 1 V). However, their short-circuit photocurrent density (JSC) has remained modest. The challenge for increasing the JSC is expected to extend the spectral response of sensitizers to the red or NIR region while maintaining efficient electron injection in the mesoscopic TiO2 film and fast regeneration by the Cu(I) complex. Here, we report two new D-A-π-A featured sensitizers coded HY63 and HY64, which employ either benzothiadiazole (BT) or phenanthrene-fused-quinoxaline (PFQ) as the auxiliary electron-withdrawing acceptor moiety. In spite of very similar energy levels and absorption onsets, HY64-based DSSCs outperform largely their HY63 counterpart, achieving an outstanding power conversion efficiency (PCE) of 12.5% with superior stability. In depth studies of interfacial charge carrier dynamics show that PFQ is superior to BT in retarding charge recombination resulting in near quantitative collection of photogenerated charge carriers.
关键词： sensitizers,light-harvesting,dye-sensitized solar cells,copper redox shuttle,charge recombination
更新于2025-09-23 15:19:57
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Evaluating the role of phenethylamine iodide as a novel anti-solvent for enhancing performance of inverted planar perovskite solar cells
摘要： Inverted perovskite solar cells (PSCs) have attracted much interest due to their improved operational stability in the past few years. However, despite the recent advances of their performance, they still suffer from low power conversion efficiencies with a reduced open-circuit voltage (Voc), as compared to PSCs with a regular structure, due to the presence of defect states. In this work, a promising and more effective strategy than the typical post-treatment passivation method is demonstrated for the decrease of nonradiative recombination in quadruple-cation RbCsMAFA inverted PSCs, through the employment of phenethylammonium iodide in the anti-solvent deposition step during the perovskite formation. As a result, a Voc value as high as 1.17 V is achieved, while control devices (where the typical chlorobenzene anti-solvent was used) exhibited a significantly lower Voc of 1.09 V. Additionally, the devices exhibited high moisture stability by maintaining nearly 80% of their initial efficiency for over 500 h exposure in ambient conditions.
关键词： efficiency,nonradiative recombination,perovskite solar cells,passivation,PEAI
更新于2025-09-23 15:19:57