Hongying Lv

New benzotrithiophene derivative with a broad band gap for high performance polymer solar cells

A new planar conjugated polymer, poly{benzo(1,2-b:3,4-b′:5,6-d′′)trithiophene-alt-4,4′-dihexyl-2,2′-bithiazole} (BTT-BTz), with a broad band gap and higher Voc based on benzotrithiophene and bithiazole units, was designed and synthesized. This copolymer possesses a deeper HOMO (−5.65 eV), and after 1,8-diiodoctane treatment, the power conversion efficiency of the photovoltaic device based on the BTT-BTz/PC71BM photoactive layer reaches 5.06% with 0.81 V of open-circuit voltage, 10.9 mA cm−2 of short-circuit current and 0.57 of fill factor, which is the highest one among the conjugated polymers based on BTT or BTz derivatives. This new conjugated copolymer seems a promising candidate for the application in tandem solar cells.

Side‐Chain Engineering for Enhancing the Thermal Stability of Polymer Solar Cells

An effective strategy of engineering side chains is proposed for enhancing solar-cell-device thermal stability. As the conjugated length of the side chains increases, the morphological stability of the blend film is enhanced. The thermal stability of corresponding devices is consequently improved.

Sol–gel transition of poly(3-hexylthiophene) revealed by capillary measurements: phase behaviors, gelation kinetics and the formation mechanism

π-Conjugated organogels of poly(3-hexylthiophene) (P3HT) are prepared via the addition of a marginal solvent, anisole, into solutions of P3HT. We initiate a novel and facile route to determine the gelation threshold of P3HT nanowire dispersions by capillary measurements. The effects of the P3HT concentration (c), anisole volume fraction (φ) and temperature (T) on the phase behaviors are discussed. A thermodynamic c–φ phase diagram is constructed, in which the P3HT dispersion is divided into four regions: solution, sol, sol–gel blend and gel. The concentration and solvent dependent sol–gel transition kinetics shows that the gelation process could be accelerated via increasing c and φ. The gelation temperature gives an exponential relationship with the concentration of P3HT and the anisole volume fraction. Morphological studies reveal the formation process and the topological structure of the P3HT microgel clusters. Based on the above results, a three-stage physical scenario for the sol–gel transition of P3HT dispersions is proposed.

Fluorinated low band gap copolymer based on dithienosilole-benzothiadiazole for high-performance photovoltaic device

A new fluorinated low band gap copolymer, poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-4,7-(5-fluoro-2,1,3-benzothiadiazole)] (PDTSBT-F), was designed and synthesized. The introduction of fluorine atom to a classical low band gap copolymer (PDTSBT) has a little influence on the polymer absorption spectrum and band gap, which was 1.48 eV for PDTSBT-F. However, the HOMO level was lowered to −5.17 eV for PDTSBT-F, the film crystallinity was improved, and PDTSBT-F showed higher charge carrier mobility than its non-fluorinated analogue (PDTSBT). For the PDTSBT-F/PC71BM device, a Jsc of 15.96 mA cm−2, a Voc of 0.70 V, and a FF of 0.60 were attained, resulting in a PCE of 6.70%. To the best of our knowledge, this is the highest value to date in devices based on copolymers with C-, Si- and Ge-bridged dithiophene as the electron-rich unit and benzothiadiazole derivatives as electron-deficient unit. A high PCE in combination with a wide absorption spectrum in the visible range could induce PDTSBT-F to be a potentially promising low band gap polymer for polymer solar cells.

Large interfacial area enhances electrical conductivity of poly(3-hexylthiophene)/insulating polymer blends

Semiconducting polymer/insulating polymer blends are promising materials for applications in organic optoelectronics. Here, two semiconducting polymer (SP)/insulating polymer (IP) blends, poly(3-hexylthiophene) (P3HT) and polystyrene (PS) or polyisoprene (PI), were prepared. The relationship between the electrical conductivity and the crystallinity/morphology of the P3HT/IP blends was systematically investigated. To prepare P3HT/IP blend films with different morphology, in particular the length-scale of phase separation, a P3HT/IP solution was obtained via mixing P3HT and IP solutions. The mixing homogeneity between P3HT and IP in the solution was controlled via tuning mixing time of the two solutions. The conductivity of the P3HT/IP blend film significantly increased with mixing time, as a consequence of decreased scale of phase separation between P3HT and IP. We therefore conclude that this enhanced conductivity of the blends is attributed to the large interfacial area between these two components of the blend, rather than crystallinity of P3HT, which presents a downward trend with increasing time. The relationship between the electrical properties and the interfacial area provides SP/IP blends with an important criterion both for scientific research and real application.

Manipulating superconductivity of 1T-TiTe2 by high pressure

Superconductivity of transition metal dichalcogenide 1T-TiTe2 under high pressure was investigated by first-principles calculations. Our results show that the superconductivity of 1T-TiTe2 exhibits very different behavior under hydrostatic and uniaxial pressure. The hydrostatic pressure is harmful to the superconductivity, while the uniaxial pressure is beneficial to the superconductivity. The superconducting transition temperature TC at ambient pressure is 0.73 K, and it reduces monotonously under the hydrostatic pressure to 0.32 K at 30 GPa, while TC increases dramatically under the uniaxial pressure along the c axis. The established TC of 6.34 K under the uniaxial pressure of 17 GPa, below which the structural stability is maintained, is above the liquid helium temperature of 4.2 K. The increase of the density of states at the Fermi level, the red-shift of the phonon density of states/Eliashberg spectral function F(ω)/α2F(ω), and the softening of the acoustic modes with pressure are considered as the main reasons that lead to the enhanced superconductivity under uniaxial pressure. In view of the previously predicted topological phase transitions of 1T-TiTe2 under the uniaxial pressure (Q. Zhang et al., Phys. Rev. B: Condens. Matter Mater. Phys., 2013, 88, 155317), we consider 1T-TiTe2 as a possible candidate in transition metal chalcogenides for exploring topological superconductivity.

Injectable shear-thinning hydrogels with enhanced strength and temperature stability based on polyhedral oligomeric silsesquioxane end-group aggregation

A strategy based on the physical association of polyhedral oligomeric silsesquioxane (POSS) end-groups was designed to reinforce shear-thinning hydrogels. Hydrogels made of the POSS-capped copolymer had significantly enhanced mechanical strength and thermal stability. This strategy provides a simple and effective method to improve the properties of shear-thinning hydrogels by tailoring the end-groups of a polymer.

Edge-controlled half-metallic ferromagnetism and direct-gap semiconductivity in ZrS2 nanoribbons

The electronic and magnetic properties of ZrS2 nanoribbons (NRs) are investigated based on first principles calculations. It is found that the ZrS2 NRs with armchair edges are all indirect band gap semiconductors without magnetism, and the band gap exhibits odd–even oscillation behavior with the increase of the ribbon width. For the NRs with zigzag edges, those with both edges S-terminated are nonmagnetic direct band gap semiconductors, and the gap decreases monotonically as a function of the ribbon width. However, the NRs with one edge S-terminated and the other edge Zr-terminated are ferromagnetic half-metals, while those with both edges Zr-terminated tend to be ferromagnetic half-metals when the width N ≥ 9. The magnetism of both systems mainly originates from the unsaturated edge Zr atoms. Depending on the different edge configurations and ribbon widths, the ZrS2 NRs exhibit versatile electronic and magnetic properties, making them promising candidates for applications in electronics and spintronics.