This paper describes synthesis and photovoltaic studies of a series of new semiconducting polymers with alternating thieno[3,4-b]thiophene and benzodithiophene units. The physical properties of these polymers were finely tuned to optimize their photovoltaic effect. The substitution of alkoxy side chains to the less electron-donating alkyl chains or introduction of electron-withdrawing fluorine into the polymer backbone reduced the HOMO energy levels of polymers. The structural modifications optimized polymers' spectral coverage of absorption and their hole mobility, as well as miscibility with fulleride, and enhanced polymer solar cell performances. The open circuit voltage, V(oc), for polymer solar cells was increased by adjusting polymer energy levels. It was found that films with finely distributed polymer/fulleride interpenetrating network exhibited improved solar cell conversion efficiency. Efficiency over 6% has been achieved in simple solar cells based on fluorinated PTB4/PC(61)BM films prepared from mixed solvents. The results proved that polymer solar cells have a bright future.

A new low band gap semiconducting polymer, PTB1, was synthesized and found promising for solar energy harvesting. Simple polymer solar cells based on PTB1 and methanofullerene [6,6]-phenyl-C(71)-butyric acid methyl esters (PC(71)BM) exhibit a solar conversion efficiency of 5.6%. An external quantum efficiency of 67% and fill-factor of 65% are achieved, both of which are among the highest values reported for a solar cell system based on a low band gap polymer.

A regioregular conjugated oligomer (MF) and its polymer counterpart (PF) containing a thieno [3,4b]thiophene moiety have been developed. The existence of thieno [3,4-b]thiophene extends the absorption of the molecules to longer wavelengths and increases the current density of solar cell devices using these materials. The regioregularity of the polymers from the incorporation of regioregular oligothiophene fragments also enhances hole mobility. Consequently, the polymers show higher solar energy conversion efficiencies in bulk heterojunction (BHJ) solar cells than the low molecular weight oligomers. Spectroscopic and structural studies reveal that composite films prepared from the polymer exhibit a larger charge carrier density and smaller domain sizes for the electron donor and acceptor than the oligomer counterpart. These results rationalize the origin for the higher solar cell efficiency.

Electric-field-driven oxygen ion evolution in the metal/oxide heterostructures emerges as an effective approach to achieve the electric-field control of ferromagnetism. However, the involved redox reaction of the metal layer typically requires extended operation time and elevated temperature condition, which greatly hinders its practical applications. Here, we achieve reversible sub-millisecond and room-temperature electric-field control of ferromagnetism in the Co layer of a Co/SrCoO2.5 system accompanied by bipolar resistance switching. In contrast to the previously reported redox reaction scenario, the oxygen ion evolution occurs only within the SrCoO2.5 layer, which serves as an oxygen ion gating layer, leading to modulation of the interfacial oxygen stoichiometry and magnetic state. This work identifies a simple and effective pathway to realize the electric-field control of ferromagnetism at room temperature, and may lead to applications that take advantage of both the resistance switching and magnetoelectric coupling.

We compare two mechanisms that dominate the temperature-dependent changes in electronic structure for poly(3-hexylthiophene-2,5 diyl) (P3HT). Structural changes in the relative orientation and configuration of the aromatic ring backbone are observed to occur over a wide range in temperature and affect the local final state screening in photoemission. There are also changes in conductivity and carrier concentration at lower temperatures leading to altered long-range intramolecular screening of photoholes and final state effects that affect excitation spectroscopies including photoemission. For polyethylenedioxythiophene (PEDOT), temperature-dependent changes in the structure and configuration of the polymer backbone are not as significant, although temperature-dependent final state effects are observed.

Two different polymers, with large local electric dipoles, are compared: copolymers of polyvinylidene fluoride with trifluoroethylene [P(VDF-TrFE, 70%:30%)] and polymethylvinylidenecyanide (PMVC). While the different local point group symmetries play a key role, both crystalline polymers exhibit intra-molecular band structure, though the Brillouin zone critical points differ.

A series of copolymers based on thieno [3,4-b]thiophene and thiophene unit have been synthesized. By controlling the ratio of thieno [3,4-b]thiophene to alkyl thiophene in the copolymer composition, the electrooptic properties of the copolymers can be fine tuned. It was shown that the energy gap of copolymers narrowed when the content of thieno [3,4-b]thiophene increased, brought by the decrease in lowest unoccupied molecular orbital and increase in highest occupied molecular orbital energy levels. When these copolymers were blended with [6,6]-phenyl-C 61 -butyric acid methyl ester to form solar cell's active layer, an optimized copolymer composition was found that gave the best photovoltaic performance. † Part of the "Larry Dalton Festschrift".

Tai, Y.; Zharnikov, M.; and Dowben, Peter A., "Electronic structure and polymerization of a self-assembled monolayer with multiple arene rings" (2006 We find evidence of intermolecular interactions for a self-assembled monolayer ͑SAM͒ formed from a large molecular adsorbate, ͓1,1Ј;4Ј,1Љ-terphenyl͔-4,4Љ-dimethanethiol, from the dispersion of the molecular orbitals with changing wave vector k. With the formation self-assembled molecular ͑SAM͒ layer, the molecular orbitals hybridize to electronic bands, with indications of significant band dispersion of the unoccupied molecular orbitals. The electronic structure is also seen to be dependent upon temperature, and cross linking between the neighbor molecules, indicating that the electronic structure may be subtly altered by changes in molecular conformation and packing.