Cedric Klein

Structure/Function Relationships in Dyes for Solar Energy Conversion: A Two-Atom Change in Dye Structure and the Mechanism for Its Effect on Cell Voltage

Recombination between injected electrons and iodine limits the photovoltage in dye-sensitized solar cells (DSSCs). We have recently suggested that many new dye molecules, intended to improve DSSCs, can accelerate this reaction, negating the expected improvement (J. Am. Chem. Soc. 2008, 130, 2907). Here we study two dyes with only a two-atom change in the structure, yet which give different V(oc)s. Using a range of measurements we show conclusively that the change in V(oc) is due solely to the increase in the recombination rate. From the structure of the dyes, and literature values for iodine binding of similar compounds, we find that it is very likely that the change in V(oc) is due solely to the difference in iodine binding at the site of the two-atom change. Using the large amount of literature on iodine complexation, we suggest structures for dyes that might show improved V(oc).

Synthesis, Characterization, and DFT/TD-DFT Calculations of Highly Phosphorescent Blue Light-Emitting Anionic Iridium Complexes

Highly phosphorescent blue-light-emitting anionic iridium complexes (C4H9)4N[Ir(2-phenylpyridine)2(CN)2] (1), (C4H9)4N[Ir(2-phenyl-4-dimethylaminopyridine)2(CN)2] (2), (C4H9)4N[Ir(2-(2,4-difluorophenyl)-pyridine)2(CN)2] (3), (C4H9)4N[Ir(2-(2,4-difluorophenyl)-4-dimethylaminopyridine)2(CN)2] (4), and (C4H9)4N[Ir(2-(3,5-difluorophenyl)-4-dimethylaminopyridine)2(CN)2] (5) were synthesized and characterized using NMR, UV-vis absorption, and emission spectroscopy and electrochemical methods. In these complexes color and quantum yield tuning aspects are demonstrated by modulating the ligands with substituting donor and acceptor groups on both the pyridine and phenyl moieties of 2-phenylpyridine. Complexes 1-5 display intense photoluminescence maxima in the blue region of the visible spectrum and exhibit very high phosphorescence quantum yields, in the range of 50-80%, with excited-state lifetimes of 1-4 micros in acetonitrile solution at 298 K. DFT and time dependent-DFT calculations were performed on the ground and excited states of the investigated complexes to provide insight into the structural, electronic, and optical properties of these systems.

Stable ⩾8% efficient nanocrystalline dye-sensitized solar cell based on an electrolyte of low volatility

We demonstrate a ⩾8% efficient nanocrystalline dye-sensitized solar cell retaining over 98% of its initial performance after 1000 h of accelerated tests subjected to thermal stress at 80 °C in the dark. Device degradation was also negligible following 1000 h of visible light soaking at 60 °C. This high performance and stable device was realized by using a robust electrolyte of low volatility in conjunction with the amphiphilic ruthenium sensitizer [Ru(4,4′-dicarboxylic acid-2,2′-bipyridine)(4,4′-bis(p-hexyloxystyryl)-2,2′-bipyridine)(NCS)2], coded as K-19, which was grafted together with 1-decylphosphonic acid on the mesoporous titania film acting as photoanode.We demonstrate a ⩾8% efficient nanocrystalline dye-sensitized solar cell retaining over 98% of its initial performance after 1000 h of accelerated tests subjected to thermal stress at 80 °C in the dark. Device degradation was also negligible following 1000 h of visible light soaking at 60 °C. This high performance and stable device was realized by using a robust electrolyte of low volatility in conjunction with the amphiphilic ruthenium sensitizer [Ru(4,4′-dicarboxylic acid-2,2′-bipyridine)(4,4′-bis(p-hexyloxystyryl)-2,2′-bipyridine)(NCS)2], coded as K-19, which was grafted together with 1-decylphosphonic acid on the mesoporous titania film acting as photoanode.

White-light phosphorescence emission from a single molecule: application to OLED

A simple mononuclear cyclometallated iridium(iii) complex exhibits white photo- and electro- luminescence in the wavelength range from 440 to 800 nm, which originates from a single emitting excited state of mixed character.

Efficient blue light-emitting diodes based on a classical “push–pull” architecture molecule 4,4′-di-(2-(2,5-dimethoxyphenyl)ethenyl)-2,2′-bipyridine

A novel, highly blue luminescent molecule containing donor and acceptor groups, 4,4′-di-(2-(2,5-dimethoxyphenyl)ethenyl)-2,2′-bipyridine, that shows photoluminescence emission at 450 nm with 43% quantum yield is designed and synthesized. Time dependent-DFT calculations show an excellent correlation between theoretical and experimental absorption spectra, thus allowing for a detailed description of the electronic structure and assignment of the main absorption features. An optimized organic light-emitting diode based on a 4,4′-di-(2-(2,5-dimethoxyphenyl)ethenyl)-2,2′-bipyridine blue emitting layer, with a 4,4′,4″-tris(carbazol-9-yl)-triphenylamine) hole transporting layer, a 2,9-dimethyl-4.7-diphenyl-phenatroline hole blocking layer, and a tris(8-hydroxyquinoline)aluminium electron transport layer exhibited 2.1% quantum efficiency.

An ester-substituted iridium complex for efficient vacuum-processed organic light-emitting diodes

An orange-red-emitting iridium complex (N958) was prepared, and its photophysical and device-based characteristics were investigated. Despite N958 displaying quite poor photophysical properties in solution (acetonitrile), organic light-emitting diode (OLED) devices based on the complex exhibit an efficiency close to 10%.