Andriy Zhugayevych

Theoretical Description of Structural and Electronic Properties of Organic Photovoltaic Materials

We review recent progress in the modeling of organic solar cells and photovoltaic materials, as well as discuss the underlying theoretical methods with an emphasis on dynamical electronic processes occurring in organic semiconductors. The key feature of the latter is a strong electron-phonon interaction, making the evolution of electronic and structural degrees of freedom inseparable. We discuss commonly used approaches for first-principles modeling of this evolution, focusing on a multiscale framework based on the Holstein-Peierls Hamiltonian solved via polaron transformation. A challenge for both theoretical and experimental investigations of organic solar cells is the complex multiscale morphology of these devices. Nevertheless, predictive modeling of photovoltaic materials and devices is attainable and is rapidly developing, as reviewed here.

Inter‐Aromatic Distances in Geobacter Sulfurreducens Pili Relevant to Biofilm Charge Transport

Dr. H. Yan Department of Chemistry and Biochemistry Center for Polymers and Organic Solids University of California at Santa Barbara Santa Barbara , CA 93106 , USA C. Chuang, Dr. A. Zhugayevych, Dr. Sergei Tretiak Theoretical Division, Los Alamos National Laboratory Los Alamos , NM 87545 , USA E-mail: serg@lanl.gov Prof. F. W. Dahlquist Department of Chemistry and Biochemistry Department of Molecular Cellular, and Developmental Biology University of California at Santa Barbara Santa Barbara , CA 93106 , USA E-mail: dahlquist@chem.ucsb.edu Prof. G. C. Bazan Department of Chemistry and Biochemistry Department of Materials Center for Polymers and Organic Solids University of California at Santa Barbara Santa Barbara , CA 93106 , USA E-mail: bazan@chem.ucsb.edu

Tailored Electronic Structure and Optical Properties of Conjugated Systems through Aggregates and Dipole−Dipole Interactions

A series of PPVO (p-phenylene vinylene oligomer) derivatives with functional groups of varying electronegativity were synthesized via the Horner-Wadsworth-Emmons reaction. Subtle changes in the end group functionality significantly impact the molecular electronic and optical properties of the PPVOs, resulting in broadly tunable and efficient UV absorption and photoluminescence spectra. Of particular interest is the NO2-substituted PPVO which exhibits photoluminescence color ranging from the blue to the red, thus encompassing the entire visible spectrum. Our experimental study and electronic structure calculations suggest that the formation of aggregates and strong dipole-dipole solute-solvent interactions are responsible for the observed strong solvatochromism. Experimental and theoretical results for the NH2-, H-, and NO2-substituted PPVOs suggest that the stabilization of ground or excited state dipoles leads to the blue or red shift of the optical spectra. The electroluminescence (EL) spectra of H-, COOH-, and NO2-PPVO have maxima at 487, 518, and 587 nm, respectively, in the OLED device. This trend in the EL spectra is in excellent agreement with the end group-dependent PL spectra of the PPVO thin-films.

Polymorphism of Crystalline Molecular Donors for Solution-Processed Organic Photovoltaics

Using ab initio calculations and classical molecular dynamics simulations coupled to complementary experimental characterization, four molecular semiconductors were investigated in vacuum, solution, and crystalline form. Independently, the molecules can be described as nearly isostructural, yet in crystalline form, two distinct crystal systems are observed with characteristic molecular geometries. The minor structural variations provide a platform to investigate the subtlety of simple substitutions, with particular focus on polymorphism and rotational isomerism. Resolved crystal structures offer an exact description of intermolecular ordering in the solid state. This enables evaluation of molecular binding energy in various crystallographic configurations to fully rationalize observed crystal packing on a basis of first-principle calculations of intermolecular interactions.

Reversible facile Rb+ and K+ ions de/insertion in a KTiOPO4-type RbVPO4F cathode material

In this paper, we report on a novel RbVPO4F fluoride phosphate, which adopts the KTiOPO4 (KTP) type structure and complements the AVPO4F (A = alkali metal) family of positive electrode (cathode) materials for metal-ion batteries. RbVPO4F was synthesized via a freeze-drying assisted solid-state route and characterized via structural, computational and electrochemical methods. RbVPO4F represents the first example of reversible electrochemical Rb+ de/insertion in a crystalline oxypolyanionic framework. The electrochemical measurements on RbVPO4F in a three-electrode cell configuration in RbClO4-saturated propylene carbonate (PC) electrolyte revealed that the material exhibits reversible Rb+ de/insertion within the 0.4–1.3 V vs. Ag+/Ag potential range (∼3.9–4.8 V vs. K+/K) displaying rather high diffusion coefficients of (0.3–1.0) × 10−11 cm2 s−1 comparable to those of K+ in KVPO4F that supports reasonably fast ionic mobility in the KTP structure despite the large ionic radius of the Rb+ ions. The energy barriers of Rb+ ion transport are exceptionally low not exceeding 0.2 eV along the c-axis and correlating well with diffusion coefficients estimated using the DFT+U-NEB methodology and with the experimentally determined transport properties. These results suggest a new paradigm for the development of materials that support many monovalent ion reversible de/insertion processes in a single prototypical structural oxypolyanionic framework.