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Significant Enhancement in Quantum Dot Light-Emitting Device Stability via a Cascading Hole Transport Layer
摘要： This work investigates the effect of the hole transport layer (HTL) on the stability of electroluminescent quantum dot light-emitting devices (QDLEDs). The electroluminescence half-life (LT50) of QDLEDs can be improved by 25x through the utilization of a cascading HTL (CHTL) structure with consecutive steps in highest occupied molecular orbital energy level. Using this approach, a LT50 of 864,000 hours (for an initial luminance of 100 cd m-2) is obtained for red QDLEDs using a conventional core/shell QD emitter. The CHTL primarily improves QDLED stability by shifting excessive hole accumulation away from the QD/HTL interface and toward the inter-layer HTL/HTL interfaces. The wider electron-hole recombination zone in the CHTL for electrons that have leaked from the QD layer results in less HTL degradation at the QD/HTL interface. This work highlights the significant influence of the HTL on QDLED stability and represents the longest LT50 for a QDLED based on the conventional core/shell QD structure.
关键词： quantum dot,EL stability,exciton-polaron interactions,QDLED,organic hole transport layer,exciton-induced degradation
更新于2025-09-23 15:19:57
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A negative polaron resistant p-type host for extended lifetime in deep blue phosphorescent organic light-emitting diodes
摘要： A novel mixed host employing a negative polaron stabilizing p-type host was developed to extend the device lifetime of blue phosphorescent organic light-emitting diodes (PhOLEDs). Instead of a conventional p-type host with only a hole transport unit, a p-type host with a negative polaron resistant unit in addition to the hole transport unit was used in the mixed host consisting of a p-type host and an n-type host. The p-type host had benzonitrile as a negative polaron resistant unit which stabilized the molecule under negative polarons. The use of the p-type host with the benzonitrile unit almost doubled the device lifetime of the blue PhOLEDs due to the improved negative polaron stability of the hosts. Therefore, the p-type host with the weak electron accepting benzonitrile unit can play the role of a lifetime extending p-type host to replace a conventional p-type host.
关键词： p-type host,device lifetime,negative polaron,benzonitrile,blue phosphorescent organic light-emitting diodes
更新于2025-09-23 15:19:57
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Understanding the effect of the carbon on the photovoltaic properties of the Cu2ZnSnS4
摘要： In this work, crystalline structure, formation energy, electronic, optical and current-voltage properties of Cu2ZnSnS4 (CZTS) with the presence of carbon (C) impurity at various sites is studied using the first-principles density functional theory (DFT) based on the generalized gradient approximation (GGA). Here, we considered possible four substitutional configurations of carbon doped CZTS supercells: Cu by C (Ccu), Cu by Zn (Czn), Sn by C (Csn) and S by C (CS). It was found that the presence of C leads to the formation of localized polarons which have dual functionality; (i) cause an increase in the scattering-limited mobility which reduces the transport efficiency, (ii) create deep acceptor level which acts as a recombination center allowing the scattering of the generated charges carriers. An enhancement in the photo-absorption is observed due to an increase in the density of states at the valence bands after the incorporation of C. This results in the efficiency enhancement by 8%. In addition, the presence of C reduces the transport efficiency and improves the photogeneration efficiency of CZTS in solar cell applications.
关键词： Carbon doped CZTS,Localized polaron,DFT,Optical properties,Solar cell,Electronic structure
更新于2025-09-23 15:19:57
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Transient Dynamics of Super Bloch Oscillations of a 1D Holstein Polaron under the Influence of an External AC Electric Field
摘要： Theoretical formalism for DC-field polaron dynamics is extended to the dynamics of a 1D Holstein polaron in an external AC electric field using multiple Davydov trial states. Effects of carrier–phonon coupling on detuned and resonant scenarios are investigated for both zero and nonzero phase. For slightly off-resonant or detuned cases, a beat between the usual Bloch oscillations and an AC driving force results in super Bloch oscillations, that is, rescaled Bloch oscillations in both the spatial and the temporal dimension. Super Bloch oscillations are damped by carrier–phonon coupling. For resonant cases, if the carrier is created on two nearest-neighboring sites, the carrier wave packet spreads with small-amplitude oscillations. Adding carrier–phonon coupling localizes the carrier wave packet. If an initial broad Gaussian wave packet is adopted, the centroid of the carrier wave packet moves with a certain velocity and with its shape unchanged. Adding carrier–phonon coupling broadens the carrier wave packet and slows down the carrier movement. Our findings may help provide guiding principles on how to manipulate the dynamics of the super Bloch oscillations of carriers in semiconductor superlattice and optical lattices by modifying DC and AC field strengths, AC phases, and detuning parameters.
关键词： Davydov Ansatz,polaron dynamics,carrier–phonon coupling,super Bloch oscillations
更新于2025-09-19 17:15:36
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Direct Observation of Structure and Dynamics of Photogenerated Charge Carriers in Poly(3-hexylthiophene) Films by Femtosecond Time-Resolved Near-IR Inverse Raman Spectroscopy
摘要： The initial charge separation process of conjugated polymers is one of the key factors for understanding their conductivity. The structure of photogenerated transients in conjugated polymers can be observed by resonance Raman spectroscopy in the near-IR region because they exhibit characteristic low-energy transitions. Here, we investigate the structure and dynamics of photogenerated transients in a regioregular poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend film, as well as in a pristine P3HT film, using femtosecond time-resolved resonance inverse Raman spectroscopy in the near-IR region. The transient inverse Raman spectrum of the pristine P3HT film at 50 ps suggests coexistence of neutral and charged excitations, whereas that of the P3HT:PCBM blend film at 50 ps suggests formation of positive polarons with a different structure from those in an FeCl3-doped P3HT film. Time-resolved near-IR inverse Raman spectra of the blend film clearly show the absence of charge separation between P3HT and PCBM within the instrument response time of our spectrometer, while they indicate two independent pathways of the polaron formation with time constants of 0.3 and 10 ps.
关键词： polaron,femtosecond inverse Raman spectroscopy,conjugated polymer,bulk heterojunction
更新于2025-09-19 17:15:36
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Heterogeneous Cationa??Lattice Interaction and Dynamics in Triple-Cation Perovskites Revealed by Infrared Vibrational Nanoscopy
摘要： Hybrid organic-inorganic perovskites exhibit extraordinary photovoltaic performance. This is believed to arise from almost liquid-like low-energy interactions among lattice ions and charge carriers. While spatial variations have recently been identified over multiple length scales in the optoelectronic responses, the relationship of the heterogeneity and the soft cation-lattice interactions has remained elusive. Here, we apply multivariate infrared vibrational nano-imaging to a formamidinium (FA)-methylammonium (MA)-cesium triple cation perovskite. By using the FA vibrational resonance as a probe of its local chemical environment, through spatial variation and correlation in composition, strength of cation-lattice coupling and its associated few-ps vibrational dynamics, we reveal how a varying local reaction field is correlated with the cation-lattice coupling. We attribute the associated heterogeneous lattice contraction to a non-uniform distribution of cesium cations. The observed varying elasticity of the lattice leads to disordered charge-phonon coupling and polaron formation, the control of which is central to improving perovskite photovoltaics.
关键词： charge-phonon coupling,infrared vibrational nano-imaging,Hybrid organic-inorganic perovskites,lattice contraction,photovoltaic performance,cation-lattice coupling,polaron formation,vibrational dynamics
更新于2025-09-19 17:13:59
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Modulation of the spin-orbit interaction and the transition probability of polaron in disk quantum dot under electromagnetic field
摘要： This work presents the important role played by the spin-orbit interaction in nanostructures such as disk quantum dot when subjected to an external field. Here by using the LLP variational method, the Rashba effect on polaron in this nanostructure with Gaussian confinement potential under electromagnetic field is investigated. The polaron ground, first excited state energy and the electron transition probability are derived. Results show that the external electromagnetic field highly modulates the spin-orbit coupling strength αr, the polaron energies and transition probability. The polaron transition probability splits in two branches due to the splitting of the eigenstates energies. Our study also reveals that DQD properties can be adjusted by the external field. Therefore, the transport and the optical properties of the quantum dot can be controlled by turning the spin-orbit coupling.
关键词： quantum dot,transition probability,spin-orbit interaction,Rashba effect,polaron
更新于2025-09-16 10:30:52
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Polarized Species in an Organic Semiconductor Laser
摘要： Meeting the challenge of direct electrically driven organic semiconductor lasers (OSLs), the design of OSL materials is under concern. Polarized species generally exist in conjugated organic materials and play an important role in the photophysics procedure; therefore, understanding these species is beneficial to designing novel OSL materials. Here, we use the amplified spontaneous emission effect as a medium to reveal a carbazole-benzothiadiazole-based polarized species that induced by charge transfer process. Spectroscopic analysis confirms that this polarized species that acted as a CT pair defect brings negative influence to both the ASE stability and solid state fluorescent quantum yield. It inspires us to be cautious for some specific molecular group combinations when designing OSL materials.
关键词： polaron,organic laser,carbazole,amplified spontaneous emission,charge transfer
更新于2025-09-12 10:27:22
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Effect of Temperature on the Single-Particle Ground-State and Self Energy of a Polar Quantum Dot with Gaussian Confinement
摘要： The temperature dependence of the properties of a polaron in a Gaussian quantum dot has been investigated by using Lee-Low-Pines-Hybrechts variational technique and quantum statistical mechanics. It is shown that the ground-state energy increases with increasing temperature and the corresponding polaronic correction decreases. It is thus shown that for entire range of the coupling constant, polaronic effects decrease with increasing temperature.
关键词： Temperature effect,Polaron self-energy,Quantum dot,Gaussian confinement
更新于2025-09-12 10:27:22
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Low-frequency dielectric dispersion in polymer-derived amorphous silicon carbonitride ceramics
摘要： Dielectric response of polymer-derived amorphous silicon carbonitride (PDC-SiCN) material was studied over a wide frequency range from 1 mHz to 10 MHz. Apart from presenting a relaxation process over 105–0.03 Hz frequency range, the material showed a strong low-frequency dielectric dispersion (LFDD), which resulted in extremely high permittivities (up to 105) at frequencies lower than 0.03 Hz. It is identified that this LFDD resulted from relaxation process was not induced by conductivity. Therefore, PDC-SiCN material showed two relaxation processes. Based on its microstructure, two polarization mechanisms were proposed for PDC-SiCN: a mechanism based on polarons generated by unpaired electrons present in the material and an interfacial polarization mechanism as a result of different properties of SiCxN4-x matrix and free-carbon clusters. Interfacial polarization process was simulated based on a parallel plate model involving two different materials. The result indicated that the relaxation time of an interfacial polarization can be distributed over a broad time range in the material.
关键词： polaron,polymer-derived ceramics,low-frequency dielectric dispersion,interfacial polarization
更新于2025-09-10 09:29:36