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%.     

Comparison of Proton Acceptor and Proton Donor Properties of H2O and H2O2 in Organic Crystals of Drug-like Compounds: Peroxosolvates vs. Crystallohydrates

Two new peroxosolvates of drug-like compounds were synthesized and studied by a combination of X-ray crystallographic, Raman spectroscopic methods, and periodic DFT computations. The enthalpies of H-bonds formed by hydrogen peroxide (H₂O₂) as a donor and an acceptor of protons were compared with the enthalpies of analogous H-bonds formed by water (H₂O) in isomorphic (isostructural) hydrates. The enthalpies of H-bonds formed by H₂O₂ as a proton donor turned out to be higher than the values of the corresponding H-bonds formed by H₂O. In the case of H₂O₂ as a proton acceptor in H-bonds, the ratio appeared reversed. The neutral O∙∙∙H-O/O∙∙∙H-N bonds formed by the lone electron pair of the oxygen atom of water were the strongest H-bonds in the considered crystals. In the paper, it was found out that the low-frequency Raman spectra of isomorphous crystalline hydrate and peroxosolvate of N-(5-Nitro-2-furfurylidene)-1-aminohydantoin are similar. As for the isostructural hydrate and peroxosolvate of the salt of protonated 2-amino-nicotinic acid and maleic acid monoanion, the Raman spectra are different.     

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.     

Long-lived electronic-deformation excitations in a polyacetylene chain — the photoexcitation spectrum

It is observed that the photoexcitation efficiency of neutral long-lived states in a trans-polyacetylene chain increases with increasing photon energy of the excitation. The observed effect is given an interpretation according to which the energy of a photon above the optical absorption edge is added to the excitation of the vibrational subsystem, increasing sharply the probability that the chain relaxes into a long-lived deformed neutral state. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 765–770 (25 May 1998)     

Effect of branching on the physical and photovoltaic properties of donor–acceptor oligomers based on triphenylamine

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Threshold formation of an intermolecular charge transfer complex of a semiconducting polymer

It has been found that the formation of an intermolecular charge transfer complex in the ground electronic state between the model conjugated polymer (poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and the low-molecular-weight organic acceptor (2,4,7-trinitrofluorenone, TNF) occurs stepwise with an increase in the acceptor concentration in the blend as is observed in the optical absorption spectra of solutions. The threshold dependence of the absorption of the charge transfer complex is attributed to the stepwise change in the concentration of the charge transfer complexes, which is not explained by the standard model describing the optical characteristics of intermolecular charge transfer complexes. A kinematic model has been proposed to explain the threshold increase in the concentration of charge transfer complexes: at low acceptor concentrations, the charge transfer complex is formed primarily on the surface of a polymer coil, whereas as the acceptor fraction in the solution increases, TNF molecules penetrate inside the polymer coils, forming the charge transfer complex with the units of the polymer inside the coil.     

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.     

Atomic composition and stability of Langmuir–Blodgett monolayers based on siloxane dimer of quaterthiophene on the surface of polycrystalline gold

Physics of the Solid State - Atomic composition of monolayers based on siloxane dimer of quaterthiophene deposited by Langmuir–Blodgett technique on a silicon dioxide surface partially...