Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

Aggregation-Induced Emission: Together We Shine, United We Soar!

Dye-sensitized solar cell (DSSC) provides credible alternative concept for inorganic solid-state photovoltaic devices. The conversion efficiency of DSSC is mainly based on the dye coated on the porous semiconductor TiO2 film. The use of natural dyes in solar cells is a promising development to this technology because it cuts down the high cost of noble metals and chemical synthesis. Therefore, this type of solar cell has attracted considerable attention from the academic and industrial communities. Numerous kinds of pigments, such as anthocyanin, carotenoid, chlorophyll, and flavonoid, extracted from various plant components, such as leaves, fruits, and flowers, have been tested as sensitizers. The photostability of the DSSC sensitizer material must be capable of undergoing many redox cycles without decomposition, and must also have the ability to carry attachment groups, such as phosphonate or carboxylate, to promptly graft it to the TiO2 oxide. This paper highlights and discusses the development of natural dye photosensitizers and the mechanisms affecting the dye stability.

Review on the development of natural dye photosensitizer for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) based on organic dyes adsorbed on oxide semiconductor electrodes, such as TiO(2), ZnO, or NiO, which have emerged as a new generation of sustainable photovoltaic devices, have attracted much attention from chemists, physicists, and engineers because of enormous scientific interest in not only their construction and operational principles, but also in their high incident-solar-light-to-electricity conversion efficiency and low cost of production. To develop high-performance DSSCs, it is important to create efficient organic dye sensitizers, which should be optimized for the photophysical and electrochemical properties of the dyes themselves, with molecular structures that provide good light-harvesting features, good electron communication between the dye and semiconductor electrode and between the dye and electrolyte, and to control the molecular orientation and arrangement of the dyes on a semiconductor surface. The aim of this Review is not to make a list of a number of organic dye sensitizers developed so far, but to provide a new direction in the epoch-making molecular design of organic dyes for high photovoltaic performance and long-term stability of DSSCs, based on the accumulated knowledge of their photophysical and electrochemical properties, and molecular structures of the organic dye sensitizers developed so far.

Photophysical and Electrochemical Properties, and Molecular Structures of Organic Dyes for Dye‐Sensitized Solar Cells

Gel-nanocomposites are rapidly emerging functional advanced materials having widespread applications in materials and biological sciences. Herein, we review syntheses, properties, and applications of various gel-nanocomposites assembled from different metal-based nanoparticles or nanocarbons [fullerene, carbon nanotubes (CNTs), and graphenes] with tailor-made supramolecular (small molecular) or polymeric physical organogels and hydrogels. Dynamic supramolecular self-assembly of gelators prove to be excellent hosts for the incorporation of these dimensionally different nanomaterials. Thus, gel-nanocomposites doped with preformed/in situ synthesized nanoparticles show magnetic or near-infrared-responsive, catalytic or antibacterial properties. Fullerene-based gel-nanocomposites show applications in organic solar cells. Gel-nanocomposites based on CNTs and graphenes and their functionalized (covalent/noncovalent) analogues find interesting properties including electrical conductivity, viscoelasticity, therma...

Soft-Nanocomposites of Nanoparticles and Nanocarbons with Supramolecular and Polymer Gels and Their Applications.

Dye-sensitized solar cells (DSSCs) are fabricated using low-cost materials and a simple fabrication process; these advantages make them attractive candidates for research on next generation solar cells. In this type of solar cell, dye-sensitized metal oxide electrodes play an important role for achieving high performance since the porous metal oxide films provide large specific surface area for dye loading and the dye molecule possesses broad absorption covering the visible region or even part of the near-infrared (NIR). Recently, metal-free sensitizers have made great progress and become the most potential alternatives. This review mainly focuses on recent progress in metal-free sensitizers for applications in DSSCs. Besides, we also briefly report DSSCs with near-infrared (NIR) organic sensitizers, which provide the possibility to extend the absorption threshold of the sensitizers in the NIR region. Finally, special consideration has been paid to panchromatic engineering, co-sensitization, a key technique to achieve whole light absorption for improving the performance of DSSCs.

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Recent progress in organic sensitizers for dye-sensitized solar cells

Fluorenylvinylenes bridged triphenylamine-based dyes with enhanced performance in dye-sensitized solar cells

Synthesis of dendritic triphenylamine derivatives for dye-sensitized solar cells

Cyanostyrene-based D–π–A type conjugated compounds bearing triphenylamine units (G1, G1-N and G2) have been synthesized. By tuning the conjugated skeleton and the electron withdrawing ability of the acceptor, green, orange and red light emitters were achieved. It is interesting that although their emissions in solutions were weak, we observed strong emission in solid states. For example, the ΦF of the dendritic molecule G2 in powder reached 0.67, which was more than 20 times of that in THF. The single crystal X-ray diffraction data revealed that the intermolecular H-bonds of C–H⋯O, C–H⋯N and C–H⋯π led to the increased rigidity of the molecular skeleton, which would restrict the intramolecular rotation, yielding high ΦF in solid states. These AIE compounds may become candidates for emitting materials.

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Aggregation-induced emission of triphenylamine substituted cyanostyrene derivatives

A series of new star-shaped monodisperse conjugated truxene derivatives bearing oligo(fluorene-vinylene) arms (Tr-OFVn, n = 1, 2, 3, 4) have been synthesized. It is found that the conjugation of the oligomers can be extended with prolonging the arms. Notably, the branched oligomers Tr-OFVn without strong donor and acceptor units exhibit two-photon absorption properties, and the two-photon absorption cross sections (δmax) increase with increasing the number of fluorene-vinylene units in the arms. The maximum value of δmax reaches 8073 GM for compound Tr-OFV4, which made it one of the most competitive compounds with enhanced TPA cross section. It provides a new platform for exploiting strong TPA compounds, in which the extended π-conjugated systems are involved in the absence of strong donor and acceptor units.

Synthesis of star-shaped monodisperse oligo(9,9-di-n-octylfluorene-2,7-vinylene)s functionalized truxenes with two-photon absorption properties

A D–π–A–π–D carbazole derivative (PCQ) with a quinoxaline moiety was designed and synthesized. Its photophysical properties in solution were studied. Moreover, PCQ was found to be a highly efficient gelator toward various apolar and polar organic solvents with the critical gelation concentrations (CGCs) as low as 0.06 wt/vol%. Spectral studies and molecular dynamic stimulation revealed that the intermolecular H-bonds and π–π stacking interactions might be responsible for guiding the self-assembly processes and the gel formation. Interestingly, PCQ could construct two-component gel with fullerene derivative driven by intermolecular hydrogen bonds. Moreover, the two-component gel film could generate photocurrent under light irradiation, indicating photo-induced electron transfer from the PCQ aggregate to the fullerene derivative.

Xin Zhao

Papers

Fluorenylvinylenes bridged triphenylamine-based dyes with enhanced performance in dye-sensitized solar cells

Synthesis of dendritic triphenylamine derivatives for dye-sensitized solar cells

Aggregation-induced emission of triphenylamine substituted cyanostyrene derivatives

Synthesis of star-shaped monodisperse oligo(9,9-di-n-octylfluorene-2,7-vinylene)s functionalized truxenes with two-photon absorption properties

Two-component gel of a D–π–A–π–D carbazole donor and a fullerene acceptor