| 1. |
- Cinquanta, Eugenio, et al.
(författare)
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Ultrafast THz Probe of Photoinduced Polarons in Lead-Halide Perovskites
- 2019
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Ingår i: Physical Review Letters. - 0031-9007. ; 122:16
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Tidskriftsartikel (refereegranskat)abstract
- We study the nature of photoexcited charge carriers in CsPbBr3 nanocrystal thin films by ultrafast optical pump-THz probe spectroscopy. We observe a deviation from a pure Drude dispersion of the THz dielectric response that is ascribed to the polaronic nature of carriers; a transient blueshift of observed phonon frequencies is indicative of the coupling between photogenerated charges and stretching-bending modes of the deformed inorganic sublattice, as confirmed by DFT calculations.
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| 2. |
- El-Zohry, Ahmed, et al.
(författare)
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Critical Role of Protons for Emission Quenching of Indoline Dyes in Solution and on Semiconductor Surfaces
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:39, s. 21346-21356
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Tidskriftsartikel (refereegranskat)abstract
- By combining time-correlated single photon counting (TCSPC) measurements, density functional theory (DFT), and time-dependent DFT (TD-DFT) calculations, we herein investigate the role of protons, in solutions and on semiconductor surfaces, for the emission quenching of indoline dyes. We show that the rhodanine acceptor moieties, and in particular the carbonyl oxygens, undergo protonation, leading to nonradiative excited-state deactivation. The presence of the carboxylic acid anchoring group, close to the rhodanine moiety, further facilitates the emission quenching, by establishing stable H-bond complexes with carboxylic acid quenchers, with high association constants, in both ground and excited states. This complexation favors the proton transfer process, at a low quencher concentration, in two ways: bringing close to the rhodanine unit the quencher and assisting the proton release from the acid by a partial-concerted proton donation from the close-by carboxylic group to the deprotonated acid. Esterification of the carboxylic group, indeed, inhibits the ground-state complex formation with carboxylic acids and thus the quenching at a low quencher concentration. However, the rhodanine moiety in the ester form can still be the source of emission quenching through dynamic quenching mechanism with higher concentrations of protic solvents or carboxylic acids. Investigating this quenching process on mesoporous ZrO2, for solar cell applications, also reveals the sensitivity of the adsorbed excited rhodanine dyes toward adsorbed protons on surfaces. This has been confirmed by using an organic base to remove surface protons and utilizing cynao-acrylic dye as a reference dye. Our study highlights the impact of selecting such acceptor group in the structural design of organic dyes for solar cell applications and the overlooked role of protons to quench the excited state for such chemical structures.
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| 3. |
- Minaev, Boris, et al.
(författare)
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Theoretical design of phosphorescence parameters for organic electro-luminescence devices based on iridium complexes
- 2009
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 358:3, s. 245-257
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Tidskriftsartikel (refereegranskat)abstract
- Tithe-dependent density functional theory with quadratic response methodology is used in order to calculate and compare spin-orbit coupling effects and the main mechanism of phosphorescence of the neutral Ir(ppy)(3) and cationic [Ir(bpy)(3)](3+) tris-iridium compounds, [Ir(ppy)(2)(bpy)](+) and [Ir(2-phenylpyridine)(2)(4,4'-tert-butyl-2,2'-bipyridine](+) complexes, including also the recently synthesised [Ir(2-phenylpyridine)(2)(4,4'-dimethylamino-2,2'-bipyridine](+) and [Ir(2,4-difluorophenylpyridine)(2)(4,4'-dimethylamino-2,2'-bipyridine](+) dyes, where ppy = 2-phenylpyridine and bpy = 2,2'-bipyridine ligands. Comparison with the symmetric, lighter and more studied [Ru(bpy)(3)](2+) and [Rh(bpy)(3)](3+) complexes is also resented. Variations in lifetimes for Ir(ppy)(3) and [Ir(bpy)(3)](3+) dyes as well as for the mixed cationic complexes are well reproduced by the quadratic response method. All the ortho-metalated iridium compounds exhibit strong phosphorescence, which is used in organic light-emitting diodes (OLEDs) to overcome the efficiency limit imposed by the formation of triplet excitons. The results from the first principle theoretical analysis of phosphorescence have helped to clarify the connections between the main features of electronic structure and the photo-physical properties of the studied heavy organometallic OLED materials.
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| 4. |
- Monti, Susanna, et al.
(författare)
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Theoretical Investigation of Adsorption, Dynamics, Self-Aggregation, and Spectroscopic Properties of the D102 Indoline Dye on an Anatase (101) Substrate
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:5, s. 2787-2796
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Tidskriftsartikel (refereegranskat)abstract
- A coherent account of adsorption modes, dynamics, self aggregation, and spectroscopic properties of an indoline organic dye adsorbed on TiO2 anatase (101) substrates is reported. The study is performed by combining reactive molecular dynamics (reaxFF) simulations with time-dependent density functional theory calculations, and the reliability of the results is assessed through comparison with theoretical and experimental data available in the literature. The use of a theoretical multilevel approach has proven to be crucial to gain a deep understanding, at an atomistic level, of the morphology and electronic properties of dye-sensitized heterogeneous interfaces. A realistic description of the functionalized anatase (101) interface, where a variety of binding modes are present, has been achieved by means of extensive molecular dynamics simulations of the adsorption of dye clusters made of different molecular units on medium/large size TiO2 anatase slabs. Our results disclose that the main driving forces toward formation of ordered surface aggregates are pi stacking and T-shaped interactions between the aromatic rings of the donor moiety of the molecules, as well as the tendency to maximize the anchoring points with the surface. The dye aggregates were found to be organized in domains, characterized by a different orientation of the packing units, and, in the high coverage limit, presenting a certain degree of short-to-medium range order.
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| 5. |
- Suo, Jiajia, et al.
(författare)
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Multifunctional sulfonium-based treatment for perovskite solar cells with less than 1% efficiency loss over 4,500-h operational stability tests
- 2024
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Ingår i: Nature Energy. - : NATURE PORTFOLIO. - 2058-7546.
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Tidskriftsartikel (refereegranskat)abstract
- The stabilization of grain boundaries and surfaces of the perovskite layer is critical to extend the durability of perovskite solar cells. Here we introduced a sulfonium-based molecule, dimethylphenethylsulfonium iodide (DMPESI), for the post-deposition treatment of formamidinium lead iodide perovskite films. The treated films show improved stability upon light soaking and remains in the black alpha phase after two years ageing under ambient condition without encapsulation. The DMPESI-treated perovskite solar cells show less than 1% performance loss after more than 4,500 h at maximum power point tracking, yielding a theoretical T80 of over nine years under continuous 1-sun illumination. The solar cells also display less than 5% power conversion efficiency drops under various ageing conditions, including 100 thermal cycles between 25 degrees C and 85 degrees C and an 1,050-h damp heat test. Suo et al. show that sulfonium-based molecules afford formamidinium lead iodide perovskites protection against environmental stress factors, improved phase stability and solar cells retaining efficiency over 4,500-h operational stability tests.
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| 6. |
- Suo, Jiajia, et al.
(författare)
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Surface Reconstruction Engineering with Synergistic Effect of Mixed-Salt Passivation Treatment toward Efficient and Stable Perovskite Solar Cells
- 2021
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Ingår i: Advanced Functional Materials. - : John Wiley & Sons. - 1616-301X .- 1616-3028. ; 31:34
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Tidskriftsartikel (refereegranskat)abstract
- Surface passivation treatment is a widely used strategy to resolve trap-mediated nonradiative recombination toward high-efficiency metal-halide perovskite photovoltaics. However, a lack of passivation with mixture treatment has been investigated, as well as an in-depth understanding of its passivation mechanism. Here, a systematic study on a mixed-salt passivation strategy of formamidinium bromide (FABr) coupled with different F-substituted alkyl lengths of ammonium iodide is demonstrated. It is obtained better device performance with decreasing chain length of the F-substituted alkyl ammonium iodide in the presence of FABr. Moreover, they unraveled a synergistic passivation mechanism of the mixed-salt treatment through surface reconstruction engineering, where FABr dominates the reformation of the perovskite surface via reacting with the excess PbI2. Meanwhile, ammonium iodide passivates the perovskite grain boundaries both on the surface and top perovskite bulk through penetration. This synergistic passivation engineer results in a high-quality perovskite surface with fewer defects and suppressed ion migration, leading to a champion efficiency of 23.5% with mixed-salt treatment. In addition, the introduction of the moisture resisted F-substituted groups presents a more hydrophobic perovskite surface, thus enabling the decorated devices with excellent long-term stability under a high humid atmosphere as well as operational conditions.
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| 7. |
- Xie, Zhen
(författare)
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High Resolution Tip-Enhanced Raman Images of Single Molecules from First Principles Simulations
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the precise control of spatially confined plasmon (SCP), tip-enhanced Raman spectroscopy (TERS) has achieved sub-nanometer resolution, leading to the chemical and physical characterization of the single molecule by optical Raman images. In the high resolution TERS measurements, the SCP spatial distribution generates the position-dependent Raman images. The position dependence challenges the conventional response theory, because the assumption of interactions between the molecule and the uniform electromagnetic field does not hold anymore. Moreover, as an emerging technology, potential applications of high resolution TERS are required to be fully explored. In this thesis, the developed theory for modeling high resolution Raman images is presented. By taking a series of typical molecular systems as examples, we theoretically predict some fine applications of single-molecule TERS.The first part of the thesis introduces the development of Raman spectroscopy and images. To achieve the final target of single molecule characterization, high spatial resolution single-molecule TERS is established and improved. As a nondestructive measuring tool, Raman imaging technology offers the means to study single molecules with unprecedented spatial resolution.The high resolution Raman images theory with detailed derivations is given in the second part of the thesis. The key factor is to take the inhomogeneous spatial distribution of SCP field into account, when we construct the interaction Hamiltonian between the localized light field and the molecule. This makes the numerical simulations of Raman images feasible.Other parts of the thesis give some theoretical predictions for potential applications of the emerging Raman imaging technology. Specifically, resonance Raman images can visualize the geometric changes of a single molecule switch and the intramolecular structure in real space. Since the localized plasmonic field can affect the electron transition, the excited quantum states can thus be effectively manipulated. This breaks down the intrinsic spatial selection rule imposed in conventional spectra. In addition, an effective linear response algorithm is used to simulate nonresonance Raman images. The unique superiority of spatial vibration resolution from non-resonance cases provides rich information about the single molecule. By constructing images from different vibrational modes, the spatial chemical distribution within a single molecule can be visualized. All these findings will facilitate fine applications of the emerging TERS technology in the coming years.
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| 8. |
- Yang, Bowen, et al.
(författare)
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A universal ligand for lead coordination and tailored crystal growth in perovskite solar cells
- 2024
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry. - 1754-5692 .- 1754-5706. ; 17:4, s. 1549-1558
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Tidskriftsartikel (refereegranskat)abstract
- Chemical environment and precursor-coordinating molecular interactions within a perovskite precursor solution can lead to important implications in structural defects and crystallization kinetics of a perovskite film. Thus, the opto-electronic quality of such films can be boosted by carefully fine-tuning the coordination chemistry of perovskite precursors via controllable introduction of additives, capable of forming intermediate complexes. In this work, we employed a new type of ligand, namely 1-phenylguanidine (PGua), which coordinates strongly with the PbI2 complexes in the perovskite precursor, forming new intermediate species. These strong interactions effectively retard the perovskite crystallization process and form homogeneous films with enlarged grain sizes and reduced density of defects. In combination with an interfacial treatment, the resulted champion devices exhibit a 24.6% efficiency with outstanding operational stability. Unprecedently, PGua can be applied in various PSCs with different perovskite compositions and even in both configurations: n-i-p and p-i-n, highlighting the universality of this ligand.
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| 9. |
- Zhou, Yang, et al.
(författare)
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How Photogenerated I2 Induces I-Rich Phase Formation in Lead Mixed Halide Perovskites
- 2023
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095.
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Tidskriftsartikel (refereegranskat)abstract
- Bandgap tunability of lead mixed halide perovskites (LMHPs) is a crucial characteristic for versatile optoelectronic applications. Nevertheless, LMHPs show the formation of iodide-rich (I-rich) phase under illumination, which destabilizes the semiconductor bandgap and impedes their exploitation. Here, it is shown that how I-2, photogenerated upon charge carrier trapping at iodine interstitials in LMHPs, can promote the formation of I-rich phase. I-2 can react with bromide (Br-) in the perovskite to form a trihalide ion I2Br- (I delta--I delta+-Br delta-), whose negatively charged iodide (I delta-) can further exchange with another lattice Br- to form the I-rich phase. Importantly, it is observed that the effectiveness of the process is dependent on the overall stability of the crystalline perovskite structure. Therefore, the bandgap instability in LMHPs is governed by two factors, i.e., the density of native defects leading to I-2 production and the Br- binding strength within the crystalline unit. Eventually, this study provides rules for the design of chemical composition in LMHPs to reach their full potential for optoelectronic devices.
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