Synthesis and photovoltaic properties of new donor-acceptor benzodithiophene-containing copolymers

Four new alternating narrow band-gap copolymers containing benzodithiophene, 4,8-dithiophen-2-yl-benzo[1,2-c;4,5-c′-bis[1,2,5]thiadiazole, 4,9-bis(thiophen-2-yl)-6,7-di(2-ethylhexyl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline, 5,8-dibromo-2,3-bis(5-octylthiophen-2-yl)quinoxaline, and 4,7-bis(5-bromothiophen-2-yl)benzo[1,2,5] thiadiazole units are synthesized under Stille reaction conditions. The structures, molecular masses, and physical properties of the copolymers are studied via ¹H NMR spectroscopy, GPC, cyclic voltammetry, and thermomechanical and thermogravimetric analyses. The polymers show solubility and a broad absorption region (with the band gap in the range from 0.81 to 1.53 eV). All of the polymers are photostable in air, and their levels of the highest occupied molecular orbital vary from ?4.98 to ?5.30 eV. Polymer solar cells based on these copolymers as donors and fullerene PC₆₀BM as an acceptor show open-circuit voltages in the range 0.16–0.61 V, and the efficiencies of the devices are in the range 0.02–0.49%.     

Synthesis of new conjugated copolymers containing 4,8-bis(dodecyloxy)benzo[1,2-b:4,5-b′]dithiophene/5,7-bis(3,4-diethylthien-2-yl)-2,3-diphenylthieno[3,4-b]pyrazine and 4,8-bis(dodecyloxy)benzo[1,2-b:4,5-b′]dithiophene/4,6-di(3,4-diethylthien-2-yl)-thieno[3,4-c][1,2,5]thiadiazole derivatives for photovoltaic applications

Two new donor-acceptor narrow-band-gap photovoltaic copolymers containing various electron-acceptor functional groups, such as thienopyrazine and thienodithiazole derivatives, are synthesized under the conditions of the Suzuki polycondensation reaction and characterized via ¹H NMR spectroscopy and GPC. The optical, electrochemical, and photovoltaic properties of the polymers are examined in detail. Both copolymers have good solubilities, high thermal stabilities, broad absorption regions (350–950 nm), relatively low levels of the highest occupied molecular orbital (?5.01 and ?5.02 eV for polymers I and II, respectively), and narrow band gaps (1.31 and 1.41 eV, respectively). Photovoltaic devices based on a polymer-II-PC₆₀BM (1: 3, wt/wt) mixture under AM 1.5 irradiation of 100 mV/cm² exhibit a power-conversion efficiency of ～0.29%, a short-circuit current of 1.45 mA/cm², an open-circuit voltage of V _oc = 0.67 V, and a fill factor of 0.30. These results are evidence that thienopyrazine functional groups are attractive as electron-acceptor building blocks in organic electronics.     

Parametric vibrations of cylindrical shells subject to geometrically nonlinear deformation: multimode models

The nonlinear parametric vibrations of cylindrical shell are described by the Donnell–Mushtari–Vlasov equations. The motions are represented as a mode expansion. Discretization is performed using the Bubnov–Galerkin method. The describing-function method is used to study traveling waves and nonlinear normal modes in systems with and without dissipation     

Synthesis of n-type conjugated polymers for bulk heterojunction solar cells

A new conjugated alternating donor-acceptor copolymer is synthesized from perylene diimide and the benzodithiophene derivative via the Suzuki reaction. Temperatures corresponding to the 10% weight loss of the copolymer in air and argon are 336 and 362°C. The copolymer is soluble in common organic solvents. The maxima of absorption spectra of the copolymer in chloroform solution and thin films are at 456 and 567 and at 444 and 567 nm, respectively. The optical band gap, as calculated from the onset of the absorption spectrum, is 1.74 eV, and the electrochemical band gap is 1.89 eV. The energies of HOMO and LUMO derived from the onset of the first oxidation and reduction potential of the cyclic voltamperogram are ?5.97 and ?4.08 eV. It is found that the solar cell with copolymer-to-poly(3-hexylthiophene) = 1: 1 features the best characteristics: The open circuit voltage is 0.54 V, the short circuit current is 0.976 mA/cm², the fill factor is 0.397, and the efficiency is 0.14%. The conjugated polymer based on perylene diimide belongs to the class of n-type polymers and shows promise as an acceptor material for all-polymer bulk heterojunction solar cells.     

Methods and computer codes for nuclear systems calculations

Some numerical methods for reactor cell, sub-critical systems and 3D models of nuclear reactors are presented. The methods are developed for steady states and space-time calculations. Computer code TRIFON solves space-energy problem in (X, Y) systems of finite height and calculates heterogeneous few-group matrix parameters of reactor cells. These parameters are used as input data in the computer code SHERHAN solving the 3D heterogeneous reactor equation for steady states and 3D space-time neutron processes simulation. Modification of TRIFON was developed for the simulation of space-time processes in sub-critical systems with external sources. An option of SHERHAN code for the system with external sources is under development.      

Approximation by Piecewise Constant Functions on a Square

In this paper we consider several algorithms for approximating functions defined on the unit square I = [0,1]² and ranging in $\mathbb{R}^2 $ . We use functions of zeroth-order Lagrange spline type as the approximation apparatus. They differ from the standard Lagrange splines on the plane by the rule for choosing grid lines according to which the spline is constructed; namely, a set of one-dimensional splines is used instead of a family of parallel lines determining the interpolation nodes.     

New narrow-band-gap conjugated copolymers based on benzodithiophene: Synthesis and photovoltaic properties

Four new alternating narrow-band-gap copolymers based on benzodithiophene are synthesized under conditions of the Stille reaction. In comparison to benzodithiophene homopolymers, all these copolymers show good solubility in common organic solvents and broad absorption in the visible spectrum of sunlight. The band gaps of the polymer films, as estimated from the cyclic voltammetry data, vary within 1.34–2.28 eV, and the position of the highest occupied molecular orbital lies in the range 4.99–5.72 eV. The values of the open-circuit voltage and the efficiency of polymer solar cells based on the copolymers are within 0.22–0.65 V and 0.02–0.48%, respectively.     

Synthesis, photophysical, and electrochromic properties of new triarylamino-containing polyphenylquinoxalines

New triarylamino-containing bis(α-diketones) are synthesized. On the basis of these compounds, a series of electrochromic organosoluble polyphenylquinoxalines with glass-transition temperatures of 224–315°C are prepared. All polymers intensively fluoresce in solutions and thin films with maxima at 535–600 and 530–560 nm, respectively. Cyclic voltammograms of polyphenylquinoxalines exhibit reversible redox properties in the range E _1/2 = 0.92–1.25 eV. It is shown that, after 15 cycles, all polymers preserve high stability and reversibility of electrochromic characteristics, but their color changes from yellow (neutral form) to wine red (oxidized form).