Fosong Wang

Dithienocarbazole and Isoindigo based Amorphous Low Bandgap Conjugated Polymers for Efficient Polymer Solar Cells

Three highly rigid and planar low-bandgap conjugated polymers comprising alternate isoindigo and dithienocarbazole groups are synthesized for the fabrication of high performance polymer solar cells. Power conversion efficiencies of up to 7.2% for conventional devices and 8.2% for inverted devices are demonstrated.

Novel NIR-absorbing conjugated polymers for efficient polymer solar cells: effect of alkyl chain length on device performance

Three low bandgap conjugated polymers, i.e., PDTPBT-C8, PDTPBT-C6 and PDTPBT-C5, which consist of alternating N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole and 2,1,3-benzothiadiazole units and carry 1-octylnonyl, 1-hexylheptyl and 1-pentylhexyl as side chains, respectively, were synthesized. These polymers show strong absorption in the wavelength range of 600–900 nm with enhanced absorption coefficient as the length of alkyl chain decreases. The film morphology of the polymers and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-61 (PCBM) blends is also dependent on the alkyl chain length. As the length decreases, the film becomes more uniform and the domian size decreases from 400–900 nm for PDTPBT-C8 to ∼50 nm for PDTPBT-C5. Bulk heterojunction photovoltaic solar cells (PSCs) were fabricated based on the blend of the polymers and PCBM with a weight ratio of 1:3. The device performance is dramatically improved as the length of the side chain decreases, due to enhanced film absorption coefficient and improved film morphology. With the polymer PDTPBT-C5, which carries the shortest alkyl chain, power conversion efficiency (PCE) up to 2.80% has been achieved. This result indicates that optimizing the structure of the solublizing alkyl chain is also crucial for the design and synthesis of high performance PSC polymeric materials.

From Tunneling to Hopping: A Comprehensive Investigation of Charge Transport Mechanism in Molecular Junctions Based on Oligo(p-phenylene ethynylene)s

The charge transport mechanism of oligo(p-phenylene ethynylene)s with lengths ranging from 0.98 to 5.11 nm was investigated using modified scanning tunneling microscopy break junction and conducting probe atomic force microscopy methods. The methods were based on observing the length dependence of molecular resistance at single molecule level and the current-voltage characteristics in a wide length distribution. An intrinsic transition from tunneling to hopping charge transport mechanism was observed near 2.75 nm. A new transitional zone was observed in the long length molecular wires compared to short ones. This was not a simple transition between direct tunneling and field emission, which may provide new insights into transport mechanism investigations. Theoretical calculations provided an essential explanation for these phenomena in terms of molecular electronic structures.

Monodisperse Co-oligomer Approach toward Nanostructured Films with Alternating Donor-Acceptor Lamellae

A series of donor-acceptor (D-A) co-oligomers with oligo(fluorene-alt-bithiophene) and perylene diimide as donor and acceptor segments, respectively, have been designed and synthesized. They can self-assembly into alternating D-A lamellar nanostructured films with the periods depending on the molecular length. These films have been successfully used in fabrication of high-performance single-molecular solar cells with power conversion efficiency up to 1.50%.

Self-host blue-emitting iridium dendrimer with carbazole dendrons: nondoped phosphorescent organic light-emitting diodes.

A blue-emitting iridium dendrimer, namely B-G2, has been successfully designed and synthesized with a secondgeneration oligocarbazole as the dendron, which is covalently attached to the emissive tris[2-(2,4-difluorophenyl)-pyridyl]iridium(III) core through a nonconjugated link to form an efficient self-host system in one dendrimer. Unlike small molecular phosphors and other phosphorescent dendrimers, B-G2 shows a continuous enhancement in the device efficiency with increasing doping concentration. When using neat B-G2 as the emitting layer, the nondoped device is achieved without loss in efficiency, thus giving a state-of-art EQE as high as 15.3% (31.3 cdA1, 28.9 lmW1) along with CIE coordinates of (0.16, 0.29).

Solution-Processable Carbazole-Based Conjugated Dendritic Hosts for Power-Efficient Blue-Electrophosphorescent Devices

A novel class of hosts suitable for solution processing has been developed based on a conjugated dendritic scaffold. By increasing the dendron generation, the highest occupied molecular orbital (HOMO) energy level can be tuned to facilitate hole injection, while the triplet energy remains at a high level, sufficient to host high-energy-triplet emitters. A power-efficient blue-electrophosphorescent device based on H2 is presented.

Novel hole-transporting materials based on 1,4-bis(carbazolyl)benzene for organic light-emitting devices

Novel hole-transporting molecules containing 1,4-bis(carbazolyl)benzene as a central unit and different numbers of diphenylamine moieties as the peripheral groups have been synthesized and characterized. These compounds are thermally stable with high glass transition temperatures of 141–157 °C and exhibit chemically reversible redox processes. Their amorphous state stability and hole transport properties can be significantly improved by increasing the number of diphenylamine moieties in the outer part and by controlling the symmetry of the carbazole-based molecules. These compounds can be used as good hole-transporting materials for organic electroluminescent (EL) devices. The device performance based on tri- and tetra-substituted carbazole derivatives is comparable to that of a typical 4,4′-bis[N-(1-naphthyl)-N-phenylamino] biphenyl (NPB)-based device.

Design of star-shaped molecular architectures based on carbazole and phosphine oxide moieties: towards amorphous bipolar hosts with high triplet energy for efficient blue electrophosphorescent devices

With a carbazole moiety as the electron donor and a phosphine-oxide moiety as the electron acceptor, two novel star-shaped bipolar hosts, 4,4′,4″-tri(N-carbazolyl)triphenylphosphine oxide (TCTP) and 3,6-bis(diphenylphosphoryl)-9-(4′-(diphenylphosphoryl)phenyl)carbazole (TPCz), have been designed and synthesized. Their topology structure differences are that the phosphine-oxide moiety is located in the molecular centre and the periphery for TCTP and TPCz, respectively. The star-shaped architecture imparts them with high decomposition temperatures (Td: 497 °C for TCTP and 506 °C for TPCz) and results in the formation of a stable amorphous glassy state (Tg: 163 °C for TCTP and 143 °C for TPCz), while the phosphine oxide linkage ensures the disrupted conjugation and the high triplet energy (>3.0 eV). In addition, both TCTP and TPCz possess a bipolar transporting capability. However, TCTP mostly transports holes and TPCz primarily conducts electrons. On the basis of appropriate device configurations, high performance blue electrophosphorescent devices with comparable efficiency (35.0–36.4 cd A−1, 15.9–16.7%) have been realized using TCTP and TPCz as the host for the blue phosphor, respectively. Compared with the unipolar host, 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA, 15.9 cd A−1, 7.8%), the efficiency is improved by more than two-fold. As far as the obtained state-of-the-art performance is concerned, we think that these novel materials should provide an avenue for the design of amorphous bipolar hosts with high triplet energy used for blue PhOLEDs on a star-shaped scaffold.

3D Nanocomposite Architectures from Carbon‐Nanotube‐Threaded Nanocrystals for High‐Performance Electrochemical Energy Storage

Better electrode architecture: spherical assemblies of electrochemically active nanocrystals threaded with carbon nanotubes are made using a simple solvation-induced-assembly process. This architecture provides the composites with mechanical robustness, effective ion- and electron-transport pathways, enabling the fabrication of electrodes with high rate, high capacity, and long cycling stability.

A Novel, Bipolar Polymeric Host for Highly Efficient Blue Electrophosphorescence: a Non‐Conjugated Poly(aryl ether) Containing Triphenylphosphine Oxide Units in the Electron‐Transporting Main Chain and Carbazole Units in Hole‐Transporting Side Chains

A novel, bipolar polymeric host based on a poly(aryl ether) containing phosphine oxide units in the electron-transporting main chain and carbazole units in the hole-transporting side chains is designed and synthesized for blue electrophosphorescence. This polymeric host possesses a bipolar character and a high E(T) of 2.96 eV. The efficiency of blue-emitting PhPLEDs based on this polymeric host doped with Flrpic reaches 23.3 cd A(-1) (EQE = 10.8%).