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[IEEE 2019 IEEE International Conference on Engineering Veracruz (ICEV) - Boca del Rio, Veracruz, Mexico (2019.10.14-2019.10.17)] 2019 IEEE International Conference on Engineering Veracruz (ICEV) - A review on quantum dot solar cells: properties, materials, synthesis and devices
摘要： Quantum dot semiconductors have gain great attraction for the development of high efficiency solar cells due to remarkable optoelectronic properties such as tunable bandgap, multiple exciton generation (MEG) and high extinction coefficient. Despite quantum dot solar cells having theoretical power conversion efficiency of about 66%, actual maximum efficiency is only 16.6%. So, it is important to further understand the relations between properties, elements composition, material structures and synthesis methods, as well as devices architectures in order to propose strategies addressed to close the gap between actual and theoretical power conversion efficiencies. This article exposes the advances related to materials and methods of synthesis, and their impact in quantum dot properties. It also introduces some recent quantum dot solar cells designs.
关键词： multiple exciton generation,quantum dots,photovoltaic device,solar cell
更新于2025-09-12 10:27:22
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Time dependent correlations of entangled states with nondegenerate branches and possible experimental realization using singlet fission
摘要： The spin-entangled exciton states produced by singlet fission provide an experimental route to generate entangled states with nondegenerate branches. Nondegenerate entangled pair states possess an internal "clock" that leads to quantum beating in various detected quantities. The implications of this internal clock for Bell’s inequality measurements and correlated particle detection are analyzed using two- and three-state spin models. In a Bell’s inequality experiment, we find that the choice of detection times can determine whether quantum or classical correlations are observed. The conditions under which the detection events could be time- or spacelike separated are analyzed in order to clarify how the temporal evolution of one particle can influence the time-dependent detection probability of the other. Possible routes to the detection of individual correlated triplet excitons are discussed, emphasizing both physical questions concerning the separation and propagation of triplet excitons over macroscopic distances and experimental challenges concerning decoherence, detection, and interpretation of the signals. We argue that spin-entangled triplet exciton states produced by singlet fission could provide a new way to probe entangled state detection and collapse, complementing schemes based on polarization-entangled photon states.
关键词： detection,Bell’s inequality,correlated particle detection,spin-entangled exciton states,nondegenerate branches,triplet excitons,quantum beating,singlet fission,decoherence
更新于2025-09-12 10:27:22
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Electrically tuning many-body states in a Coulomb-coupled InAs/InGaSb double layer
摘要： We study the transport properties of an electron-hole double layer consisting of barrier-separated InAs/InGaSb quantum wells. We focus on measurements of four-terminal resistivity of a Hall-bar sample as a function of electron (n) and hole (p) density, that are being tuned by a pair of top and bottom gates. In zero magnetic ?eld, we clearly observe an insulating phase which occurs at a charge neutral point, below a critical carrier density n = p < 1 × 1011 cm?2. This phase is characterized by a narrow and thermally activated resistance peak and an anomalous Hall resistance. This observation reinforces our previous ?nding of an excitonic insulator. Remarkably, when the layer densities are being tuned into imbalance, here p (cid:2) n, a broader resistance peak emerges. We discuss this phase with respect to a possible (theoretically predicted) charge density wave ground state. Both phases can persist above ～25 K, indicating robust correlations in the electron-hole double layers.
关键词： electron-hole double layer,exciton condensation,InAs/InGaSb quantum wells,quantum spin Hall effect,charge density wave
更新于2025-09-12 10:27:22
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Hole Transfer Originating from Weakly Bound Exciton Dissociation in Acceptor–Donor–Acceptor Nonfullerene Organic Solar Cells
摘要： The underlying hole-transfer mechanism in high-efficiency OSC bulk heterojunctions based on acceptor?donor?acceptor (A?D?A) nonfullerene acceptors (NFAs) remains unclear. Herein, we study the hole-transfer process between copolymer donor J91 and five A?D?A NFAs with different highest occupied molecular orbital energy offsets (ΔEH) (0.05?0.42 eV) via ultrafast optical spectroscopies. Transient absorption spectra reveal a rapid hole-transfer rate with small ΔEH, suggesting that a large energy offset is not required to overcome the exciton binding energy. Capacitance?frequency spectra and time-resolved photoluminescence spectra confirm the delocalization of an A?D?A-structured acceptor exciton with weak binding energy. Relative to the hole-transfer rate, hole-transfer efficiency is the key factor affecting device performance. We propose that holes primarily stem from weakly bound acceptor exciton dissociation, revealing a new insight into the hole-transfer process in A?D?A NFA-based OSCs.
关键词： hole-transfer mechanism,organic solar cells,exciton dissociation,ultrafast optical spectroscopies,nonfullerene acceptors
更新于2025-09-12 10:27:22
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Influence of electric field on direct and indirect exciton in a concentrically coupled quantum ring heterostructure embedded in SiO2 matrix
摘要： Excitonic states of Concentric Double Quantum Ring (CDQR) heterostructures embedded in SiO2 matrix under the influence of electric field has been calculated theoretically using variational technique. CDQR has been confined in a quantum well of suitable width which serve as the height of the quantum ring along which the electric field is applied. Central barrier width, outer ring width and carrier location has been tuned to understand the localization of both direct and indirect excitons. Effect of ring dimension and electric field on the energy states of Inner Ring Exciton (IRE) and Outer Ring Exciton (ORE) has been determined. Tilting of conduction and valence bands due to the application of electric field invokes a triangular confinement to the carriers and the same has been discussed. Diamagnetic susceptibility which is merely an indicator of electron hole separation and intersubband transition energy has also been calculated for both symmetric and asymmetric quantum ring. Height of the QR has also been changed to study its effect on the diamagnetic susceptibility of an exciton.
关键词： Diamagnetic Susceptibility,Quantum Ring,Exciton,Binding energy,Electric Field
更新于2025-09-12 10:27:22
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High detectivity organic photodetectors in the visible light wavelength with ternary bulk heterojunction
摘要： In this work, we report an ternary bulk heterojunction (t-BHJ) organic photodetectors (OPDs) based on P3HT, PTB7 and PC61BM. The effects of PTB7 added to P3HT:PC61BM on the optical and electrical properties of OPDs were investigated. It is found that when the mass ratio of P3HT:PTB7:PC61BM is 8:2:10, the response spectrum of the active layer is extended to 780 nm, The responsivity (R) and external quantum efficiency (EQE) of the OPDs are reached 178, 291, 241 mA/W and 35%, 68%, 65%, under 630, 530, and 460 nm illumination and ?1 V bias, respectively, and the detectivity (D*) reached 1012 Jones. The results show that the addition of PTB7 with appropriate mass ratio can increases the exciton generation and dissociation probability in P3HT:PC61BM, which increases the photocurrent of the device. In addition, the addition of PTB7 promotes the crystallization of the film, reduces the density of trap defects in the film, and reduces the dark current of the device.
关键词： Microscopic morphology,Organic photodetectors,Ternary bulk heterojunction,Exciton dissociation
更新于2025-09-12 10:27:22
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Exciton binding energy in cubic semiconductor quantum dot
摘要： In this paper, the exciton binding energy in a cubic semiconductor nanostructure quantum dot has been investigated by using variational method. Results show that in cubic quantum dot with a size of 50 ?A, will have the most exciton binding energy.
关键词： variational method,binding energy,Exciton,quantum dot
更新于2025-09-12 10:27:22
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Exciton Coherence Length and Dynamics in Graphene Quantum Dot Assemblies
摘要： Exciton size and dynamics were studied in assemblies of two well-defined graphene quantum dots of varying size: hexabenzocoronene (HBC), where the aromatic core consists of 42 C atoms, and carbon quantum dot (CQD) with 78 C atoms. The synthesis of HBC and CQD were achieved using bottom-up chemical methods, while their assembly was studied using steady-state UV/vis spectroscopy, X-ray scattering, and electron microscopy. While HBC forms long ordered fibers, CQD was found not to assemble well. The exciton size and dynamics were studied using time-resolved laser spectroscopy. At early times (~100 fs), the exciton was found to delocalize over ~1?2 molecular units in both assemblies, which reflects the confined nature of excitons in carbon-based materials and is consistent with the calculated value of ~2 molecular units. Exciton?exciton annihilation measurements provided the exciton diffusion lengths of 16 and 3 nm for HBC and CQD, respectively.
关键词： Time-resolved Laser Spectroscopy,Graphene Quantum Dot,Hexabenzocoronene,Exciton,Carbon Quantum Dot
更新于2025-09-12 10:27:22
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Influence of single-walled carbon nanotubes induced exciton dissociation improvement on hybrid organic photovoltaic devices
摘要： Torch-plasma-grown single-walled carbon nanotubes (SWCNTs) are integrated with regioregular poly(3-hexylthiophene) (P3HT) and a fullerene derivative 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 (PCBM) as a hybrid photoactive layer for bulk heterojunction solar cell devices. We demonstrate that molecular information could be accurately obtained by time-of-flight secondary ion mass spectrometry through the hybrid organic photoactive solar cell layers when sputtering is performed using a Cs+ 2000 eV ion source. Furthermore, the photovoltaic (PV) performance of the fabricated devices show an increase in the short-circuit current density (Jsc) and the fill factor (FF) as compared to the pristine devices fabricated without SWCNTs. The best results are obtained with 0.5 wt. % SWCNT loads, where an open-circuit voltage (VOC) of 660 mV is achieved, with a Jsc of 9.95 mA cm?2 and a FF of 54%, leading to a power conversion efficiency of 3.54% (measured at standard test conditions, AM1.5 g). At this optimum SWCNT concentration of 0.5 wt. %, and to further understand the charge-transfer mechanisms taking place at the interfaces of P3HT:PCBM:SWCNT, Jsc is measured with respect to the light intensity and shows a linear dependency (in the double logarithmic scale), which implies that losses in the charge carrier are rather governed by monomolecular recombination. Finally, our results show that our hybrid devices benefit from the fullerene electron accepting nature and from the SWCNT fast electron transportation feature that improve substantially the exciton dissociation efficiency. The influence of the SWCNTs on the Fermi level and the work function of the photoactive composite and its impact on the PV performance is also investigated.
关键词： single-walled carbon nanotubes,bulk heterojunction,PCBM,hybrid organic photovoltaic devices,photovoltaic performance,P3HT,exciton dissociation
更新于2025-09-12 10:27:22
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Exciton-phonon properties in cylindrical quantum dot with parabolic confinement potential under electric field
摘要： The mixed confinement potential effect on exciton in cylindrical quantum dot (QD) is calculated in the presence of an electric field with and without confined longitudinal optical (LO) phonon mode contribution. The variational approach within the effective mass approximation is used to describe the exciton-phonon interaction with three variational parameters of the trial wave function. The ground state binding energy of exciton has been calculated numerically for the parabolic (axial direction) and square (lateral direction) finite confinement potentials under the electric field applied along the growth direction of the QD. The system both with and without LO-phonon contribution is investigated. The combined effects of applied electric field and parabolic confinement on the ground state binding energy, the polaronic correction and the Stark shift are examined in detail. The findings indicate that the electric field strongly reduces the binding energy in both ignoring and considering LO-phonon interaction especially for wider thickness of QD. We have shown that the contribution of LO-phonon leads to an increase in the binding energy and to decrease in the Stark shift energy. Furthermore, our numerical results illustrate a strong dependence of Stark shift on the QD height, electric field strength and LO-phonon contribution.
关键词： Parabolic potential,Electric field,Binding energy,Exciton-LO-phonon,Stark shift
更新于2025-09-12 10:27:22