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Di‐fluorinated Oligothiophenes for High‐Efficiency All‐Small‐Molecule Organic Solar Cells: Positional Isomeric Effect of Fluorine Substitution on Performance Variations
摘要： Three symmetrically di-fluorinated organic semiconductors (namely D5T2F-P, D5T2F-S, and D5T2F-T) containing rhodanine-flanked pentathiophene structures are synthesized and used as donors in all-small-molecule organic solar cells (ASM-OSCs) prepared with the small-molecule acceptor 2,2'-((2Z,2'Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC-4F). The different substitutional positions of the fluorine atoms (-F) in the conjugated backbone of the donor molecule leads to various material and photovoltaic properties being exhibited. Among the three isomers, the centrally-fluorinated D5T2F-P exhibits a redshifted absorption spectrum, downshifted highest occupied molecular orbital (HOMO) energy level, and improved miscibility with IDIC-4F in the blend films, all of which result in superior device performance. The power conversion efficiency (PCE) of the ASM-OSCs based on D5T2F-P:IDIC-4F reaches the impressive value of 9.36% with an open-circuit voltage (VOC) value of 0.86 V and a short-circuit current density (JSC) value of 16.94 mA/cm2, while those of D5T2F-S (6.11%) and D5T2F-T (5.42%) are much lower. In comparison, an ASM-OSC based on the non-fluorinated analogue DRCN5T fabricated under the same conditions exhibits poorer performance (8.03% with IDIC-4F), revealing a 16% enhancement in PCE achieved through backbone fluorination. To the best of our knowledge, the PCE of 9.36% is one of the highest efficiencies of oligothiophene-based ASM-OSCs reported in the literature to date.
关键词： organic solar cells,binding energy,small molecule donors,fluorination,non-fullerene
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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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-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
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Surface Modification for Improving the Photocatalytic Polymerization of 3,4-Ethylenedioxythiophene over Inorganic Lead Halide Perovskite Quantum Dots
摘要： Inorganic lead halide perovskite quantum dots (iLHP-QDs) have recently been used in the photocatalytic reaction. However, the factors that influence the photocatalytic performance of the iLHP-QDs has not been fully investigated. Herein, we synthesised a series of iLHP-QDs with varied halide ratio (CsPbX3, X=I, I0.67Br0.33, I0.5Br0.5, I0.33Br0.67, Br) and studied its influence on the photocatalytic performance by monitoring the polymerization of TerEDOT. The CsPbI3 QDs showed the best performance owing to its narrow bandgap and low exciton binding energy. Moreover, the photocatalytic performance of the iLHP-QDs could be simply improved by being treated with methyl acetate, which can be attributed to the replacement of the oleic acid by the short acetate acid, and the introduction of the traps on the surface of QDs in the post-treatment. These results could help design more efficient photocatalytic system and further promote the application of iLHP-QDs.
关键词： photocatalytic performance,quantum dots,exciton binding energy,charge transport efficiency,halide perovskite
更新于2025-09-11 14:15:04
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Reference Module in Materials Science and Materials Engineering || Excitonic Model versus Band Gap Model in Organic Materials
摘要： The binding energy Eb of an optical excitation is a key parameter for the understanding of the opto-electronic properties of organic solids in general and of conjugated polymers in particular. It controls the dissociation of an electronic excitation of either singlet or triplet character into a pair of free charges as well as the reverse process, i.e., the recombination of an electron–hole (eh) pair yielding an excitation that can decay radiatively or nonradiatively. If Eb is large, photogeneration of charge carriers is an endothermic, inefficient process. It is obvious that in an organic solar cell (OSC) one would like Eb to be as small as possible, while in a light emitting diode (LED) it is the opposite because charge recombination requires a driving force. In this article an outline of the problem of defining the exciton binding in a molecular solid will be presented followed by experimental and theoretical advances and a critical review of relevant conceptual frameworks with particular emphasis on conjugated polymers.
关键词： Organic Materials,Conjugated Polymers,Band Gap Model,Opto-electronic Properties,Exciton Binding Energy
更新于2025-09-11 14:15:04
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Extremely reduced dielectric confinement in two-dimensional hybrid perovskites with large polar organics
摘要： Two dimensional inorganic–organic hybrid perovskites (2D perovskites) suffer from not only quantum confinement, but also dielectric confinement, hindering their application perspective in devices involving the conversion of an optical input into current. In this report, we theoretically predict that an extremely low exciton binding energy can be achieved in 2D perovskites by using high dielectric-constant organic components. We demonstrate that in (HOCH2CH2NH3)2PbI4, whose organic material has a high dielectric constant of 37, the dielectric confinement is largely reduced, and the exciton binding energy is 20-times smaller than that in conventional 2D perovskites. As a result, the photo-induced excitons can be thermally dissociated efficiently at room temperature, as clearly indicated from femtosecond transient absorption measurements. In addition, the mobility is largely improved due to the strong screening effect on charge impurities. Such low dielectric-confined 2D perovskites show excellent carrier extraction efficiency, and outstanding humidity resistance compared to conventional 2D perovskites.
关键词： dielectric confinement,humidity resistance,carrier mobility,exciton binding energy,2D perovskites
更新于2025-09-10 09:29:36
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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || In Situ Photoelectron Spectroscopy
摘要： X-ray photoelectron spectroscopy (XPS) is based on the photoelectric effect, which is the emission of electrons from a solid, liquid, or gas once excited with photons (ultraviolet radiation or X-rays or even g-rays) of sufficient energy. XPS measured thus the occupied states. It is not the intensity of the radiation, which causes the emission, but the wavelength l, which is related with their frequency n and energy Ephoton via the relations Ephoton = hn = hc/l of the photons. The kinetic energy Ekin of such photoelectrons yields a spectrum which allows for the determination of the binding energy EB of electrons expelled from the core levels, and the binding energy of hybridized states is Ekin = Ephoton - EB - 4spectrometer; 4 is the work function of the spectrometer. relationship between measured variables in the valence band. The quantitative
关键词： X-ray photoelectron spectroscopy,photoelectric effect,binding energy,work function,valence band
更新于2025-09-10 09:29:36
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Identification of the shallow donor state in Sb doped ZnO by photoluminescence excitation spectroscopy
摘要： Photoluminescence excitation (PLE) spectroscopy was used to investigate the optical properties of the recently discovered 3364.3 meV antimony-related donor bound exciton (D0X) in zinc oxide. By suitable control of the growth conditions, we achieved samples in which the Sb-related donor emission was the dominant near-bandgap luminescence feature. Resonant excitation using a tunable UV source enabled the observation of the two electron transitions of the donor bound exciton, enabling the direct determination of the binding energy of the Sb donor at 42:2 + 0:5 meV, the lowest value yet reported for a donor in this material. The two electron transitions exhibit an unusual blue shift with increasing temperature, which is explained in terms of thermalization of excited states of the D0X initial state. The D0X excited states were probed by PLE and follow the trends of conventional shallow group III donors such as Al, Ga, and In.
关键词： binding energy,two electron transitions,shallow donor state,Photoluminescence excitation spectroscopy,Sb doped ZnO
更新于2025-09-09 09:28:46
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Excitonic complexes in anisotropic atomically thin two-dimensional materials: Black phosphorus and
摘要： The effect of anisotropy in the energy spectrum on the binding energy and structural properties of excitons, trions, and biexcitons is investigated. To this end we employ the stochastic variational method with a correlated Gaussian basis. We present results for the binding energy of different excitonic complexes in black phosphorus (bP) and TiS3 and compare them with recent results in the literature when available, for which we find good agreement. The binding energies of excitonic complexes in bP are larger than those in TiS3. We calculate the different average interparticle distances in bP and TiS3 and show that excitonic complexes in bP are strongly anisotropic whereas in TiS3 they are almost isotropic, even though the constituent particles have an anisotropic energy spectrum. This is also confirmed by the correlation functions.
关键词： biexciton,TiS3,binding energy,black phosphorus,trion,anisotropy,stochastic variational method,exciton
更新于2025-09-09 09:28:46