Guankui Long

A Series of Simple Oligomer-like Small Molecules Based on Oligothiophenes for Solution-Processed Solar Cells with High Efficiency

A series of acceptor-donor-acceptor simple oligomer-like small molecules based on oligothiophenes, namely, DRCN4T-DRCN9T, were designed and synthesized. Their optical, electrical, and thermal properties and photovoltaic performances were systematically investigated. Except for DRCN4T, excellent performances were obtained for DRCN5T-DRCN9T. The devices based on DRCN5T, DRCN7T, and DRCN9T with axisymmetric chemical structures exhibit much higher short-circuit current densities than those based on DRCN6T and DRCN8T with centrosymmetric chemical structures, which is attributed to their well-developed fibrillar network with a feature size less than 20 nm. The devices based on DRCN5T/PC71BM showed a notable certified power conversion efficiency (PCE) of 10.10% under AM 1.5G irradiation (100 mW cm(-2)) using a simple solution spin-coating fabrication process. This is the highest PCE for single-junction small-molecule-based organic photovoltaics (OPVs) reported to date. DRCN5T is a rather simpler molecule compared with all of the other high-performance molecules in OPVs to date, and this might highlight its advantage in the future possible commercialization of OPVs. These results demonstrate that a fine and balanced modification/design of chemical structure can make significant performance differences and that the performance of solution-processed small-molecule-based solar cells can be comparable to or even surpass that of their polymer counterparts.

Small Molecules Based on Benzo(1,2-b:4,5-b')dithiophene Unit for High-Performance Solution-Processed Organic Solar Cells

Small molecules, namely, DCAO(3)TBDT and DR(3)TBDT, with 2-ethylhexoxy substituted BDT as the central building block and octyl cyanoacetate and 3-ethylrhodanine as different terminal units with the same linkage of dioctyltertthiophene, have been designed and synthesized. The photovoltaic properties of these two molecules as donors and fullerene derivatives as the acceptors in bulk heterojunction solar cells are studied. Among them, DR(3)TBDT shows excellent photovoltaic performance, and power conversion efficiency as high as 7.38% (certified 7.10%) under AM 1.5G irradiation (100 mW cm(-2)) has been achieved using the simple solution spin-coating fabrication process, which is the highest efficiency reported to date for any small-molecule-based solar cells. The results demonstrate that structure fine turning could cause significant performance difference and with that the performance of solution-processed small-molecule solar cells can indeed be comparable with or even surpass their polymer counterparts.

Porous 3D graphene-based bulk materials with exceptional high surface area and excellent conductivity for supercapacitors

Until now, few sp2 carbon materials simultaneously exhibit superior performance for specific surface area (SSA) and electrical conductivity at bulk state. Thus, it is extremely important to make such materials at bulk scale with those two outstanding properties combined together. Here, we present a simple and green but very efficient approach using two standard and simple industry steps to make such three-dimensional graphene-based porous materials at the bulk scale, with ultrahigh SSA (3523 m2/g) and excellent bulk conductivity. We conclude that these materials consist of mainly defected/wrinkled single layer graphene sheets in the dimensional size of a few nanometers, with at least some covalent bond between each other. The outstanding properties of these materials are demonstrated by their superior supercapacitor performance in ionic liquid with specific capacitance and energy density of 231 F/g and 98 Wh/kg, respectively, so far the best reported capacitance performance for all bulk carbon materials.

High‐Performance Solar Cells using a Solution‐Processed Small Molecule Containing Benzodithiophene Unit

A conjugated small molecule containing a benzodithiophene unit shows high performance in bulk heterojunction (BHJ) solar cells. Using the simple solution spinning process, a high PCE is achieved by employing this molecule as the donor in BHJ solar cells.

Graphene - a promising material for organic photovoltaic cells.

As a promising two-dimensional nanomaterial with outstanding electronic, optical, thermal, and mechanical properties, graphene has been proposed for many applications. In this Progress Report we summarize and discuss comprehensively the advances made so far for applications of graphene in organic photovoltaic (OPV) cells, including that for transparent electrodes, active layers and interfaces layer in OPV. It is concluded that graphene may very likely play a major role in new developments/improvements in OPVs. The future studies for this area are proposed to focus on the following: i) improving the conductivity without comprising the transparency as a transparent electrode material; ii) controlling the sheet sizes, band structure and surface morphology for use as a electron acceptor material, and iii) controlling and improving the functionalization and compatibility with other materials as interface layer material.

Controlling the Effective Surface Area and Pore Size Distribution of sp2 Carbon Materials and Their Impact on the Capacitance Performance of These Materials

A series of sp(2) carbon materials with different specific surface area (SSA) and controlled pore size distribution (PSD) were synthesized at large scale through a facile and low-cost method. The SSA and PSD of these carbon materials were controlled by using different carbon sources and preparation methods. With different total and effective SSA (E-SSA) and PSD, the impacts on their capacitance performance were investigated thoroughly, which demonstrated that both E-SSA and PSD played the most important roles in their capacitance performance. Furthermore, theoretical modeling was performed, and the results are in agreement with the experimental results for the influence of E-SSA and PSD on their capacitance performance. Based on these, a general model using the slit/cylindrical NL-DFT approach is proposed for the estimation of the specific capacitance of sp(2) carbon materials, which offers a simple but reliable method to predict the capacitance performance of these materials, thus speeding up the design and screening of the materials for high-performance supercapacitor and other surface area related devices.

A perylene diimide (PDI)-based small molecule with tetrahedral configuration as a non-fullerene acceptor for organic solar cells

In this paper, a new perylene diimide (PDI)-based acceptor Me-PDI4 with tetrahedral configuration (or 3D) has been synthesized and characterized. Solution-processed organic solar cells (OSCs) based on Me-PDI4 have been investigated and our results show that the device performance can reach as high as 2.73%. Our new design with tetrahedral configuration (or 3D) could be an efficient approach to increase the PCE of OSCs with non-fullerene acceptors.

Synthesis, Structure, and Air‐stable N‐type Field‐Effect Transistor Behaviors of Functionalized Octaazanonacene‐8,19‐dione

Increasing the length of N-heteroacenes or their analogues is highly desirable because such materials could have great potential applications in organic electronics. In this report, the large π-conjugated N-heteroquinone 6,10,17,21-tetra-((triisopropylsilyl)ethynyl)-5,7,9,11,16,18,20,22-octaazanonacene-8,19-dione (OANQ) has been synthesized and characterized. The as-prepared OANQ shows high stability under ambient conditions and has a particularly low LUMO level, which leads to it being a promising candidate for air-stable n-type field-effect transistors (FETs). In fact, FET devices based on OANQ single crystals have been fabricated and an electron mobility of up to 0.2 cm(2) V(-1) s(-1) under ambient conditions is reported. More importantly, no obvious degradation was observed even after one month. Theoretical calculations based on the single crystal are consistent with the measured mobility.

Efficient solution processed bulk-heterojunction solar cells based a donor–acceptor oligothiophene

A solution processed small molecule with low band gap, dicyanovinyl-substituted oligothiophene (DCN7T), was used as the donor in bulk heterojunctions solar cells and a power conversion efficiency of 2.45% has been obtained for the device using simply spin-coating without special treatment.

Pushing Up Lithium Storage through Nanostructured Polyazaacene Analogues as Anode

According to the evidence from both theoretical calculations and experimental findings, conjugated ladder polymers containing large π-conjugated structure, a high number of nitrogen heteroatoms, and a multiring aromatic system, could be an ideal organic anode candidate for lithium-ion batteries (LIBs). In this report, we demonstrated that the nanostructured polyazaacene analogue poly(1,6-dihydropyrazino[2,3g]quinoxaline-2,3,8-triyl-7-(2H)-ylidene-7,8-dimethylidene) (PQL) shows high performance as anode materials in LIBs: high capacity (1750 mAh g(-1), 0.05C), good rate performance (303 mAh g(-1), 5C), and excellent cycle life (1000 cycles), especially at high temperature of 50 °C. Our results suggest nanostructured conjugated ladder polymers could be alternative electrode materials for the practical application of LIBs.