Kun Lu

Conjugated Polymer–Small Molecule Alloy Leads to High Efficient Ternary Organic Solar Cells

Ternary organic solar cells are promising candidates for bulk heterojunction solar cells; however, improving the power conversion efficiency (PCE) is quite challenging because the ternary system is complicated on phase separation behavior. In this study, a ternary organic solar cell (OSC) with two donors, including one polymer (PTB7-Th), one small molecule (p-DTS(FBTTH2)2), and one acceptor (PC71BM), is fabricated. We propose the two donors in the ternary blend forms an alloy. A notable averaged PCE of 10.5% for ternary OSC is obtained due to the improvement of the fill factor (FF) and the short-circuit current density (J(sc)), and the open-circuit voltage (V(oc)) does not pin to the smaller V(oc) of the corresponding binary blends. A highly ordered face-on orientation of polymer molecules is obtained due to the formation of an alloy structure, which facilitates the enhancement of charge separation and transport and the reduction of charge recombination. This work indicates that a high crystallinity and the face-on orientation of polymers could be obtained by forming alloy with two miscible donors, thus paving a way to largely enhance the PCE of OSCs by using the ternary blend strategy.

Synergistic Effect of Polymer and Small Molecules for High‐Performance Ternary Organic Solar Cells

A ternary blend system with two donors and one acceptor provides an effective route to improve the performance of organic solar cells. A synergistic effect of polymer and small molecules is observed in ternary solar cells, and the power conversion efficiency (PCE) of the ternary system (8.40%) is higher than those of binary systems based on small molecules (7.48%) or polymers (6.85%).

Flexible and Binder-Free Organic Cathode for High-Performance Lithium-Ion Batteries

Fabrication of a flexible organic electrode by growing polyimide nanoflakes on single-wall carbon nanotube films is presented. The flexible electrode exhibits high capacity and outstanding rate capability. This electrode is promising for the application in high-power flexible lithium-Ion batteries.

Solution‐Processed Solid Solution of a Novel Carbazole Derivative for High‐Performance Blue Phosphorescent Organic Light‐Emitting Diodes

Blue light: Incorporation of two fluorenyl rings into a phenyl group at the C9 position of fluorene builds a bulky and rigidly tetrahedral framework, which is functionalized by two carbazole groups. This molecule possesses excellent thermal and morphological stability, miscibility to the phosphorescent dopant, and high triplet energy, leading to narrow blue phosphorescent emission.

An organic cathode material based on a polyimide/CNT nanocomposite for lithium ion batteries

In this paper, a 3,4,9,10-perylenetetracarboxylic dianhydride/carbon nanotube (PTCDA/CNT) nanocomposite and its corresponding polymer nanocomposite poly(3,4,9,10-perylenetetracarboxylic dianhydride ethylene diamine)/carbon nanotube (PI/CNT) were produced, which could be used as organic cathode materials for lithium ion batteries. Compared with PTCDA, PTCDA/CNT exhibited an enhanced rate capability, and the capacity was increased from 10 mA h g−1 to 115 mA h g−1 at 2 C. Polymerization can further increase the cycling stability of organic cathode materials. The capacity of the polymer nanocomposite PI/CNT remained at 93% after 300 cycles under a current of 100 mA g−1, while the capacity of PTCDA/CNT was only 74% after 300 cycles. The improved electrochemical properties of these materials were ascribed to increased electronic conductivity of PTCDA due to the formation of composites with CNTs, and their decreased solubility in the electrolyte due to polymerization.

Oligomeric Donor Material for High‐Efficiency Organic Solar Cells: Breaking Down a Polymer

Dr. L. Yuan, Dr. J. Zhang, Dr. Y. Zhang, Dr. L. Zhu, Dr. K. Lu, Prof. Z. Wei National Center for Nanoscience and Technology Beijing 100190 , China E-mail: lvk@nanoctr.cn; weizx@nanoctr.cn Dr. L. Yuan, Prof. Z. Wei University of Chinese Academy of Sciences Beijing 100049 , China Dr. Y. Zhao, Prof. W. Yan Department of Environmental Science and Engineering Xi’an Jiaotong University Xi’an 710049 , China

Synthesis, Structures, and Properties of Fused Thiophenes for Organic Field‐Effect Transistors

A series of fused thiophenes composed of fused alpha-oligothiophene units as building blocks, end-capped with either styrene or 1-pentyl-4-vinylbenzene groups, has been synthesized through Stille coupling reactions. The compounds have been fully characterized by means of (1)H NMR spectrometry, high-resolution mass spectrometry, and elemental analysis. The molecules present a trans-trans configuration between their double bonds, which has been verified and confirmed by Fourier-transform infrared spectroscopy and single-crystal X-ray diffraction analysis. The X-ray crystal structures showed pi-pi overlap and sulfur-sulfur interactions between the adjacent molecules. The decomposition temperatures were all found to be above 300 degrees C, indicating that compounds of this series possess excellent thermal stability. The fact that no phase transition occurs at low temperature indicates that they should be well-suited for application in devices. Moreover, they possess low HOMO energy levels, based on cyclic voltammetry measurements, and suitable energy gaps, as determined from their thin-film UV/Vis spectra. Thin-film X-ray diffraction analysis and atomic force microscopy revealed high crystallinity on supporting substrates. In addition, as the substrate temperature has a significant influence on the morphology and the degree of crystallinity, the device performance could be optimized by varying the substrate temperature. These materials were found to exhibit optimal field-effect performance, with a mobility of 0.17 cm(2) V(-1) s(-1) and an on/off ratio of 10(5), at a substrate temperature of 70 degrees C.

Large-Area Polyimide/SWCNT Nanocable Cathode for Flexible Lithium-Ion Batteries.

A large-area flexible polymer electrode is fabricated using a new type of polyimide/single-walled carbon nanotube (SWCNT) nanocable composite. SWCNTs serve as the current collector and conductive network, and polyimide nanoparticles anchored on carbon nanotubes act as active materials. The electrode shows superior rate performance, good cycling stability, and high flexibility.

Phenyl-substituted fluorene-dimer cored anthracene derivatives: highly fluorescent and stable materials for high performance organic blue- and white-light-emitting diodes

A new series of highly fluorescent blue-emitting materials based on fluorene and anthracene hybrids are designed and synthesized for organic light-emitting diodes (OLEDs). These materials feature a phenyl-substituted fluorene dimer as a bulky and rigid core and anthracene as a functional active group. The novel use of a phenyl-substituted fluorene dimer as building skeleton to design functional molecules is reported for the first time. The thermal, photophysical, electrochemical, and electroluminescent (EL) properties are presented, as well as combined density functional study of their geometry and electronic structure. These compounds show excellent thermal resistance with high glass transition temperature (Tg) in the range 159–257 °C, thermal decomposition temperature (Td) 441–495 °C, and high fluorescent quantum yield (ΦF = 0.61–0.96, relative to 9,10-diphenylanthracene) as well as good film-forming and morphological stability. Remarkably, high-performance blue OLEDs are also fabricated in a simple three-layer device architecture using these compounds as emissive layer with luminance efficiency of 2.2–5.1 cd A−1 as a non-doped blue emitter and even higher efficiency of up to 13.6 cd A−1 and maximum external quantum efficiency 4.8% is obtained when doped a blue fluorescent dye, 4,4′-(1E,1′E)-2,2′(biphenyl-4,4′diyl)bis(ethane-2,1-diyl)bis(N,N-dip-tolyaniline) (DPAVBi). Furthermore, we fabricate highly efficient fluorescent white OLEDs employing an interesting emission in the longer wavelength of one of our compound combined with DPAVBi emission to achieve stable white light emission in a binary blend single emissive layer with high efficiency of 14.8 cd A−1 (5.3 lm W−1) and maximum brightness of 50248 cd m−2.

Acceptor End‐Capped Oligomeric Conjugated Molecules with Broadened Absorption and Enhanced Extinction Coefficients for High‐Efficiency Organic Solar Cells

Acceptor end-capping of oligomeric conjugated molecules is found to be an effective strategy for simultaneous spectral broadening, extinction coefficient enhancement, and energy level optimization, resulting in profoundly enhanced power conversion efficiencies (of 9.25% and 8.91%) compared to the original oligomers. This strategy is effective in overcoming the absorption disadvantage of oligomers and small molecules due to conjugation limitation.