Li-Min Xiao

Highly efficient and stable organic sensitizers with duplex starburst triphenylamine and carbazole donors for liquid and quasi-solid-state dye-sensitized solar cells

Two new D–D–π–π–A type stable organic sensitizers, DT3 and DW3, were successfully synthesized for dye-sensitized solar cells (DSSCs). DT3 displayed η values of 10.03% and 8.05% in liquid and quasi-solid-state DSSCs, respectively, under standard global 1.5 solar conditions, offering an example achieving the highest efficiency to date in quasi-solid-state DSSCs based on pure organic dyes.

Starburst triarylamine based dyes bearing a 3,4-ethylenedioxythiophene linker for efficient dye-sensitized solar cells.

Starburst triarylamine-based organic dyes (D1, D2, and D3) have been synthesized. For the three designed dyes, the starburst triarylamine group, thiophene (or 3,4-ethylenedioxythiophene), and cyanoacetic acid take the role of electron donor, π-conjugation bridge, and electron acceptor, respectively. These compounds are characterized by photophysical, electrochemical, and theoretical computational methods. Nanocrystalline TiO2-based dye-sensitized solar cells were fabricated using these molecules as light-harvesting sensitizers. The overall efficiencies of the sensitized cells range from 5.48 to 6.15%. It was found that the introduction of the EDOT group in D3 bathochromically extended the absorption spectra, resulting in a leap in the photovoltaic performance in comparison to D2. Incorporation of a hydrophobic carbazole-containing segment at D2 relative with D1 retarded the electron transfer from TiO2 to the oxidized dye or electrolyte, leading to an increase of electron lifetime.

A multifunctional poly-N-vinylcarbazole interlayer in perovskite solar cells for high stability and efficiency: a test with new triazatruxene-based hole transporting materials

The hydrophobic and conductive polymer poly-N-vinylcarbazole (PVK) has been successfully utilized as a multifunctional interlayer between perovskite and the hole transporting material (HTM) for highly stable and efficient perovskite solar cells (PSCs) for the first time. The very thin PVK interlayer can not only protect the perovskite structure from moisture and degradation, but also modulate the interface to reduce charge recombination and promote hole transportation simultaneously. Benefited by coupling this PVK-protection method with the molecular design of an economical and synthetically facile triazatruxene-based HTM (SP-12) featuring good stability, planarity and hole mobility, a reliable power conversion efficiency of 18.8% has been achieved, which is superior to that using the well-studied spiro-OMeTAD (16.9%), demonstrating a promising fabrication approach to efficient and long-term stable PSCs.

Stable organic dyes based on the benzo[1,2-b:4,5-b′]dithiophene donor for efficient dye-sensitized solar cells

Two novel arylamine-free organic compounds (CYF1 and CYF2) incorporating a substituted benzo[1,2-b:4,5-b′]dithiophene unit as the electron donor were synthesized and used as sensitizers for dye-sensitized solar cells (DSSCs). The relationship between the chemical structure and photovoltaic performance was investigated. A higher molar absorption coefficient, longer electron lifetime, and larger adsorption amount were observed for sensitizer CYF1, which contains a single π bridge and anchoring unit, compared with CYF2 with twin π bridges and anchoring units. As a result, under standard global AM 1.5 solar conditions, the device based on CYF1 sensitizer gave a higher conversion efficiency of 8.02% than that based on CYF2. This is the highest value for amine-free organic sensitizers with no strong donor units. Moreover, the CYF1- and CYF2-sensitized DSSCs exhibited excellent stability under 1000 W m2 light soaking at 60 °C for 600 h. This is the first example of organic sensitizers based on benzo[1,2-b:4,5-b′]dithiophene donors for efficient dye-sensitized solar cells.

Regio- and Enantioselective Photodimerization within the Confined Space of a Homochiral Ruthenium/Palladium Heterometallic Coordination Cage

The photoinduced regio- and enantioselective coupling of naphthols and derivatives thereof is achieved in the confined chiral coordination space of a RuII metalloligand based cage. The racemic or enantiopure cages encapsulate naphthol guests, which then undergo a regiospecific 1,4-coupling, rather than the normal 1,1-coupling, to form 4-(2-hydroxy-1-naphthyl)-1,2-napthoquinones; moderate stereochemical control is achieved with homochiral cages. The photoreactions proceed under both aerobic and anaerobic conditions but through distinct pathways that nevertheless involve the same radical intermediates. This unusual dimerization constitutes a very rare example of asymmetric induction in biaryl coupling by making use of coordination cages with dual functionality-photoredox reactivity and stereoselectivity.

Multichromophoric di-anchoring sensitizers incorporating a ruthenium complex and an organic triphenyl amine dye for efficient dye-sensitized solar cells

Multichromophoric dye-sensitized solar cells (DSSCs) based on the dual sensitization with a metal–organic combinatorial dye comprised of a ruthenium complex and an organic triphenyl amine dyad have been constructed, which convert light into electrical energy with a higher power conversion efficiency and incident-photon-to-current efficiency than the devices made of individual inorganic and organic dyes.

Dye‐Sensitized Solar Cells with Improved Performance using Cone‐Calix[4]Arene Based Dyes

Three cone-calix[4]arene-based sensitizers (Calix-1-Calix-3) with multiple donor-π-acceptor (D-π-A) moieties are designed, synthesized, and applied in dye-sensitized solar cells (DSSCs). Their photophysical and electrochemical properties are characterized by measuring UV/Vis absorption and emission spectra, cyclic voltammetry, and density functional theory (DFT) calculations. Calix-3 has excellent thermo- and photostability, as illustrated by thermogravimetric analysis (TGA) and dye-aging tests, respectively. Importantly, a DSSC using the Calix-3 dye displays a conversion efficiency of 5.48 % in under standard AM 1.5 Global solar illumination conditions, much better than corresponding DSSCs that use the rod-shaped dye M-3 with a single D-π-A chain (3.56 %). The dyes offer advantages in terms of higher molar extinction coefficients, longer electron lifetimes, better stability, and stronger binding ability to TiO2 film. This is the first example of calixarene-based sensitizers for efficient dye-sensitized solar cells.

Novel phenanthroline-based ruthenium complexes for dye-sensitized solar cells: enhancement in performance through fluoro-substitution

Three new ruthenium sensitizers [Ru(H2dcbpy)(LX)(NCS)2] [H2dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine, and LX = 2-(4-fluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (RuLF), 4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-N,N-dimethylaniline (RuLN), or 2-(4-methylphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (RuLC)], have been designed and synthesized. Under standard global AM 1.5 solar conditions, the device using the RuLF sensitizer gave a conversion efficiency of 7.28%, compared to 7.50% optimized for the N719 dye. The power-conversion efficiency of RuLF is 24% and 66% higher than those of RuLN and RuLC, respectively, due to a remarkable fluoro-substitution effect. The origins of this effect have been thoroughly investigated by spectroscopic, electrochemical, and density functional theory (DFT) studies. Our results show the fluoro-substitution serves as the key factor for improving the device performance, the role of which is to increase the dye density on TiO2, alter the molecular packing, and tune the electron donating property. These findings may provide an alternative strategy for the design of a new type of ruthenium sensitizer by the introduction of C–F bonds to the auxochromic ligand to improve the device performance.

Fluorescent calix[4]arene chemosensor for acidic and basic amino acids in pure aqueous media

A modified calix[4]arene based receptor 2, conjugated with four bithiophene–cyanoacrylic acid groups, not only recognizes acidic amino acids (Asp and Glu) by quenching fluorescence, but also shows highly selective sensing for basic amino acids (Lys and Arg) by turning on fluorescence in sodium phosphate buffer solution without any organic solvent. The UV-Vis spectroscopy binding analysis and ESI-MS studies indicate that the above complexes have a 1 : 1 stoichiometry. 1H NMR and molecular modeling studies suggest a supramolecular complex structure like the relationship between a lid and cup, but not a typical host-guest relationship of the cavity. A plausible mechanism involving intramolecular charge transfer (ICT) is proposed.

Performance Improvement for Dye-sensitized Solar Cells with Cone-calix[4]arene Based Dyes

Invited for the cover of this issue is the group of Jun-Min Liu and Cheng-Yong Su at Sun Yat-Sen University. The image shows that cone-calix[4]arene-based dye flowers can develop in the field of dye-sensitized solar cells as sunflowers thrive under sunshine. The Full Paper itself is available at 10.1002/cssc.201402401