Yingjie Zhao

Interfacial Synthesis of Conjugated Two-Dimensional N-Graphdiyne

We explored the interfacial synthesis of 2D N-graphdiyne films at the gas/liquid and liquid/liquid interfaces. Triazine- or pyrazine-based monomers containing ethynyl group were polymerized through the Glaser coupling reactions at interfaces. Several layered, highly ordered and conjugated 2D N-graphdiyne were obtained. Their structures were characterized by TEM, SEM, AFM, XPS, and Raman spectra. Thin films with minimum thickness of 4 nm could be prepared.

Efficient Hydrogen Production on a 3D Flexible Heterojunction Material

A novel heterojunction material, with electron-rich graphdiyne as the host and molybdenum disulfide as the catalytic center (eGDY/MDS), to produce ultraefficient hydrogen-evolution reaction (HER) at all pH values is described. It is a surprise that the metallic conductor combined from two semiconductor materials, eGDY and MDS, leads to optimal free energy (ΔGH ) and enhancement in the intrinsic HER catalytic performances. The calculated and experimental results indicate that eGDY/MDS shows greatly enhanced catalytic activities and high stabilities in both acidic and alkaline conditions; these approach the outstanding performances of the state-of-the-art noble-metal-based catalysts. The eGDY/MDS shows better activity than Pt/C in alkaline media and remarkable enhancement in photocurrent density. The high catalytic activity of eGDY/MDS originates from facilitated electronic transfer kinetics, high conductivity, more exposed catalytic active sites, and excellent mass transport.

Controllable Spatial Configuration on Cathode Interface for Enhanced Photovoltaic Performance and Device Stability

The molecular structure of cathode interface modification materials can affect the surface morphology of the active layer and key electron transfer processes occurring at the interface of polymer solar cells in inverted structures mostly due to the change of molecular configuration. To investigate the effects of spatial configuration of the cathode interfacial modification layer on polymer solar cells device performances, we introduced two novel organic ionic salts (linear NS2 and three-dimensional (3D) NS4) combined with the ZnO film to fabricate highly efficient inverted solar cells. Both organic ionic salts successfully decreased the surface traps of the ZnO film and made its work function more compatible. Especially NS4 in three-dimensional configuration increased the electron mobility and extraction efficiency of the interfacial film, leading to a significant improvement of device performance. Power conversion efficiency (PCE) of 10.09% based on NS4 was achieved. Moreover, 3D interfacial modification could retain about 92% of its initial PCE over 160 days. It is proposed that 3D interfacial modification retards the element penetration-induced degradation without impeding the electron transfer from the active layer to the ZnO film, which significantly improves device stability. This indicates that inserting three-dimensional organic ionic salt is an efficient strategy to enhance device performance.

Highly Conjugated Three-Dimensional Covalent Organic Frameworks Based on Spirobifluorene for Perovskite Solar Cell Enhancement

Highly conjugated three-dimensional covalent organic frameworks (3D COFs) were constructed based on spirobifluorene cores linked via imine bonds (SP-3D-COFs) with novel interlacing conjugation systems. The crystalline structures were confirmed by powder X-ray diffraction and detailed structural simulation. A 6- or 7-fold interpenetration was formed depending on the structure of the linking units. The obtained SP-3D-COFs showed permanent porosity and high thermal stability. In application for solar cells, simple bulk doping of SP-3D-COFs to the perovskite solar cells (PSCs) substantially improved the average power conversion efficiency by 15.9% for SP-3D-COF 1 and 18.0% for SP-3D-COF 2 as compared to the reference undoped PSC, while offering excellent leakage prevention in the meantime. By aid of both experimental and computational studies, a possible photoresponsive perovskite-SP-3D-COFs interaction mechanism was proposed to explain the improvement of PSC performance after SP-3D-COFs doping.

Synthetic Two-dimensional Organic Structures

Synthetic two-dimensional (2D) polymers have totally different topology structures compared with traditional linear or branched polymers. The peculiar 2D structures bring superior properties. Although, from linear to 2D polymers, the study of these new materials is still in its infancy, they already show potential applications especially in optoelectronics, membranes, energy storage and catalysis, etc. In this review, we summarize the recent progress of the 2D materials from three respects: (1) Chemistry—different types of polymerization reactions or supramolecular assembly to construct the 2D networks were described; (2) Preparation methods—surface science, crystal engineering approaches and solution synthesis were introduced; (3) Functionalization and some early applications.

Ultrafastly Interweaving Graphdiyne Nanochain on Arbitrary Substrates and Its Performance as a Supercapacitor Electrode

A moderate method is first developed here for superfast (in seconds) growth of an ultrafine graphdiyne (GDY) nanochain on arbitrary substrates in the atmosphere. This is an environmentally friendly and metal-catalyst-free method, efficiently eliminating extraneous contaminations for the carbon materials. The seamless GDY coating on any substrates demonstrates that an all-carbon GDY possesses outstanding controllability and processability, perfectly compensating for the drawbacks of prevailing all-carbon materials. After the decoration of 3D GDY nanostructures, the substrates become superhydrophobic with contact angles high up to of 148° and can be used as outstanding frameworks for storing organic pollution. Because of the reasonable porous and 3D continuous features, the as-prepared samples can be applied as high-performance binder-free supercapacitor electrodes with high area capacitance of up to 53.66 mF cm -2, prominent power performance, and robust long-term retention (99% after 1300 cycles).

Preparation of N-Graphdiyne Nanosheets at Liquid/Liquid Interface for Photocatalytic NADH Regeneration

Two-dimensional (2D) N-graphdiyne (N-GDY) nanosheets containing different number of N were synthesized by polymerization of triazine, pyrazine, and pyridine-based monomers at liquid/liquid interface. The configurations and nanostructures of N-GDY were well-characterized. The wettability changed to more hydrophilic as the N contents increased. The collected N-GDY was further employed as metal-free photocatalyst for NADH regeneration. The catalytic performance was related with the N content in the graphdiyne. The N3-GDY demonstrated the best activity. This strategy provided a new promising platform of designing unique 2D N-GDY with tunable performance in biorelated catalysis.

Graphdiyne-Doped P3CT-K as an Efficient Hole-Transport Layer for MAPbI3 Perovskite Solar Cells

Here we reported the doping of graphdiyne in P3CT-K in MAPbI3 perovskite solar cells as hole-transport materials. The doping could improve the surface wettability of P3CT-K, and the resulting perovskite morphology was improved with homogeneous coverage and reduced grain boundaries. Simultaneously, it increased the hole-extraction mobility and reduced the recombination as well as improved the performance of devices. Therefore, a high efficiency of 19.5% was achieved based on improved short-circuit current and fill factor. In addition, hysteresis of the J- V curve was also obviously reduced. This work paves the way for the development of highly efficient perovskite solar cells.

Controlled Synthesis of a Three-Segment Heterostructure for High-Performance Overall Water Splitting

Developing earth-abundant, highly active, and robust electrocatalysts capable of both oxygen and hydrogen evolution reactions is crucial for the commercial success of renewable energy technologies. Here we demonstrate a facile and universal strategy for fabricating transition metal (TM) sulfides by controlling the atomic ratio of TM precursors for water splitting in basic media. Density functional theory calculations reveal that the incorporation of Fe/Co can significantly improve the catalytic performance. The optimal material exhibits extremely small overpotentials of 208 mV for oxygen evolution and 68 mV for hydrogen evolution at 10 mA cm-2 with robust long-term stability. The optimized material was used as bifunctional electrodes for overall water splitting, which delivers 10 mA cm-2 at a very low cell voltage of 1.44 V with robust stability over 80 h at 100 mA cm-2 without degradation, much better than the combination of Pt and RuO2 as benchmark catalysts. The excellent water-splitting performance sheds light on the promising potential of such sulfides as high activity and robust stable electrodes.