As emphasized in a recent review article (Chem. Rev. 2022, 122, 14180), organic solar cell (OSC) photoconversion efficiency has been rapidly evolving with results increasingly comparable to those of ...traditional inorganic solar cells. Historically, OSC performance improvement focused first on the morphology of P3HT:PC61BM solar cells then went through different stages to shift lately interest towards nonfullerene acceptors (NFAs) as a replacement of PC61BM acceptor (ACC) molecule. Here, we use density‐functional theory (DFT) and time‐dependent DFT to investigate four novel NFAs of A‐D‐A (acceptor‐donor‐acceptor) form derived from the recently synthesized IDIC‐4Cl (Dyes Pigm. 2019, 166, 196). Our level of theory is carefully evaluated for IDIC‐4Cl and then applied to the four novel NFAs in order to understand how chemical modifications lead to physical changes in cyclic voltammetry (CV) frontier molecular orbital energies and absorption spectra in solution. Finally we design and apply a new type of Scharber plot for NFAs based upon some simple but we think reasonable assumptions. Unlike the original Scharber plots where a larger DON band gap favors a larger PCE, our modified Scharber plot reflects the fact that a smaller ACC band gap may favor PCE by filling in gaps in the DON acceptor spectrum. We predict that only the candidate molecule with the least good acceptor A, with the highest frontier molecular orbital energies, and one of the larger CV lowest unoccupied molecular orbital (LUMO) − highest unoccupied molecular orbital (HOMO) gaps, will yield a PM6:ACC PCE exceeding that of the parent IDIC‐4Cl ACC. This candidate also shows the largest oscillator strength for the primary 1(HOMO, LUMO) charge‐ transfer transition and the largest degree of delocalization of charge transfer of any of the ACC molecules investigated here.
High performance nonfullerene acceptors based on the recently synthesized IDIC‐4CL, that can be used to build bulk heterojunction photovoltaic cells, with enhanced open circuit voltage.
Developing cost‐effective and high‐performance catalysts for oxygen evolution reaction (OER) is essential to improve the efficiency of electrochemical conversion devices. Unfortunately, current ...studies greatly depend on empirical exploration and ignore the inherent relationship between electronic structure and catalytic activity, which impedes the rational design of high‐efficiency OER catalysts. Herein, a series of bimetallic Ni‐based metal‐organic frameworks (Ni‐M‐MOFs, M = Fe, Co, Cu, Mn, and Zn) with well‐defined morphology and active sites are selected as the ideal platform to explore the electronic‐structure/catalytic‐activity relationship. By integrating density‐functional theory calculations and experimental measurements, a volcano‐shaped relationship between electronic properties (d‐band center and eg filling) and OER activity is demonstrated, in which the NiFe‐MOF with the optimized energy level and electronic structure situated closer to the volcano summit. It delivers ultra‐low overpotentials of 215 and 297 mV for 10 and 500 mA cm−2, respectively. The identified electronic‐structure/catalytic activity relationship is found to be universal for other Ni‐based MOF catalysts (e.g., Ni‐M‐BDC‐NH2, Ni‐M‐BTC, Ni‐M‐NDC, Ni‐M‐DOBDC, and Ni‐M‐PYDC). This work widens the applicability of d band center and eg filling descriptors to activity prediction of MOF‐based electrocatalysts, providing an insightful perspective to design highly efficient OER catalysts.
This work clearly demonstrates that the identified electronic‐structure/catalytic‐activity relationship can be utilized to comprehend and forecast oxygen evolution reaction activity changes induced by the substitution of transition‐metal heteroatoms (M = Fe, Co, Cu, Mn, and Zn) into Ni‐MOF, providing a general and clear path for a rational design of highly‐active and cost‐effective catalyst.
The ultrafast dynamics of photoexcited charge carriers in condensed matter systems play an important role in optoelectronics and solar energy conversion. Yet it is challenging to understand such ...multidimensional dynamics at the atomic scale. Combining the real‐time time‐dependent density functional theory with fewest‐switches surface hopping scheme, we develop time‐dependent ab initio nonadiabatic molecular dynamics (NAMD) code Hefei‐NAMD to simulate the excited carrier dynamics in condensed matter systems. Using this method, we have investigated the interfacial charge transfer dynamics, the electron–hole recombination dynamics, and the excited spin‐polarized hole dynamics in different condensed matter systems. The time‐dependent dynamics of excited carriers are studied in energy, real and momentum spaces. In addition, the coupling of the excited carriers with phonons, defects and molecular adsorptions are investigated. The state‐of‐art NAMD studies provide unique insights to understand the ultrafast dynamics of the excited carriers in different condensed matter systems at the atomic scale.
This article is categorized under:
Structure and Mechanism > Computational Materials Science
Molecular and Statistical Mechanics > Molecular Dynamics and Monte‐Carlo Methods
Electronic Structure Theory > Ab Initio Electronic Structure Methods
Software > Simulation Methods
The non adiabatic molecular dynamics have been used to investigate the excited carrier dynamics and their couplings with complex environment in condensed matter systems.
Every day, density‐functional theory (DFT) is routinely applied to computational modeling of molecules and materials with the expectation of high accuracy. However, in certain situations, popular ...density‐functional approximations (DFAs) have the potential to give substantial quantitative, and even qualitative, errors. The most common class of error is delocalization error, which is an overarching term that also encompasses the one‐electron self‐interaction error. In our opinion, its resolution remains the greatest outstanding challenge in DFT development. In this paper, we review the history of delocalization error and provide several complimentary conceptual pictures for its interpretation, along with illustrative examples of its various manifestations. Approaches to reduce delocalization error are discussed, as is its interplay with other shortcomings of popular DFAs, including treatment of non‐bonded repulsion and neglect of London dispersion.
This article is categorized under:
Electronic Structure Theory > Density Functional Theory
Delocalisation error can be rationalized in terms of three different theoretical underpinnings: fractional charge, exchange holes and electron self‐interaction. Delocalisation error causes numerous problems in the DFT field including band‐gap lowering, charge smearing, and spuriously low energy barriers.
The intrinsic spins and their correlations are the least understood characteristics of fission fragments from both theoretical and experimental points of view. In many nuclear reactions, the emerging ...fragments are typically excited and acquire an intrinsic excitation energy and an intrinsic spin depending on the type of the reactions and interaction mechanism. Both the intrinsic excitation energies and the fragments' intrinsic spins and parities are controlled by the interaction mechanism and conservations laws, which lead to their correlations and determines the character of their deexcitation mechanism. We outline here a framework for the theoretical extraction of the intrinsic spin distributions of the fragments and their correlations within the fully microscopic real-time density-functional theory formalism and illustrate it on the example of induced fission of ^{236}U and ^{240}Pu, using two nuclear energy density functionals. These fission fragment intrinsic spin distributions display new qualitative features previously not discussed in literature. Within this fully microscopic framework, we extract for the first time the intrinsic spin distributions of fission fragments of ^{236}U and ^{240}Pu as well as the correlations of their intrinsic spins, which have been debated in literature for more than six decades with no definite conclusions so far.
Supramolecular helices that arise from the self-assembly of small organic molecules via non-covalent interactions play an important role in the structure and properties of the corresponding ...materials. Here we study the supramolecular helical aggregation of oligo(phenyleneethynylene) monomers from a theoretical point of view, always guiding the studies with experimentally available data. In this way, by systematically increasing the number of monomer units, optimized n-mer geometries are obtained along with the corresponding absorption and circular dichroism spectra. For the geometry optimizations we use density functional theory together with the B3LYP-D3 functional and the 6–31G** basis set. For obtaining the spectra we resort to time-dependent density functional theory using the CAM-B3LYP functional and the 3–21G basis set. These combinations of density functional and basis set were selected after systematic convergence studies. The theoretical results are analyzed and compared to the experimentally available spectra, observing a good agreement.
PDF
