Molecular-Scale Interface Engineering of Nanocrystalline Titania by Co-adsorbents for Solar Energy Conversion

The use of mixed self-assembled monolayers, combining hydrophobic co-adsorbents with the sensitizer, has been demonstrated to enhance the efficiency of dye-sensitized solar cells (DSCs). Herein, the influence of the anchoring groups of the co-adsorbents on the performance of the DSCs is carefully examined by selecting two model molecules: neohexyl phosphonic acid (NHOOP) and bis-(3,3-dimethyl-butyl)-phosphinic acid (DINHOP). The effect of these co-adsorbents on the photovoltaic performance (JV curves, incident photon-to-electron conversion efficiency) is investigated. Photoelectron spectroscopy and electrochemical impedance spectroscopy are performed to assess the spatial configuration of adsorbed dye and co-adsorbent molecules. The photoelectron spectroscopy studies indicate that the ligands of the ruthenium complex, containing thiophene groups, point out away from the surface of TiO2 in comparison with the NCS group

Captured by Evil: The Idea of Corruption in Law

Corruption is one of the most powerful words in the English language. When it comes to the treatment of corruption by law, however, corruption is a troubled concept. With increasing recognition of the costs of corruption for economic development, democratic governance, international aid programs, and other world goals, attempts to articulate what this destructive force is have led to an avalanche of theoretical writing. In the last fifteen years, corruption has been variously defined as the violation of law, a public servant\u27s breach of public duty, an agent\u27s betrayal of a principal\u27s interests, the pursuit of secrecy, the denial of equality in political influence, and other ways. In the end, however, all of these efforts fall short. Corruption is more than law-breaking: it is more than breaching public duties. To say that A is a thief or that A has breached his duty is not to say that A is corrupt. The latter is far more powerful, far more emotional, far more essential than the others. It is more than secrecy, or the denial of equal opportunity. It is a searing indictment, somehow, not only of A\u27s act but of A\u27s character. It is a statement not only of what A has done, but of what A has become. Corruption is, I argue, a far more powerful idea than these existing legal understandings have articulated: it is the idea of capture by evil, the possession of the individual by evil, in law. Just as we once believed in corruption of the blood in American law, which decreed that offspring of those who had committed crimes were believed to be irrevocably tainted by their parents\u27 depravity, so we still retain - through the idea of corruption - the belief that individual evil extends beyond acts of wrongdoing, or the denial of equal opportunity, or breach of the public trust. It is this idea of corruption, I argue - the idea of capture by evil - that, although unarticulated, drives our understandings of corruption in law. It drives our understanding of corrupt judges, who, once corrupt, we believe will act so in every case. It drives our understanding of campaign finance reform, where we fear deep corruption of the process from the occurrence of corrupt acts. It drives our understanding of corruption as a systemic effect and systemic influence, which presents institutional dangers that are greater than other crimes, and that requires purgation rather than simple law enforcement. This Article explores this deeper understanding of corruption, its impacts in areas such as judicial corruption and campaign finance reform, and its implications for the principle of the rule of law

Photocurrent Spectra and Fast Kinetic Studies of P3HT/PCBM Mixed with a Dye for Photoconversion in the Near-IR Region

Photoconversion properties are demonstrated for a device based on a small dye molecule, absorbing light in the near-IR region, mixed with two organic charge transport materials and together forming a dye-sensitized organic bulk heterojunction. The organic dye molecule, phthalocyanine (1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine), mixed with a blend of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C-61 (PCBM), shows a photoconversion spectrum extended more than 150 nm toward longer wavelengths, as compared to a device without such dye sensitization. In the dye-sensitized region of the photoconversion spectrum the maximum infernal quantum efficiency was estimated to 40%. With higher dye concentrations the internal quantum efficiency decreases. Transient laser spectroscopy measurements show that after excitation of the dye there is an electron transfer from the dye to PCBM and a subsequent hole transfer from the dye to P3HT, which results in a long-lived (P3HT(+)/dye/PCBM-) charge-separated state

Photoelectrochemical properties of nano- to microstructured ZnO electrodes

The photoelectrochem. properties of ZnO electrodes were studied in the near-UV region. Studies were carried out on electrodes with different morphologies, porosities, and film thicknesses to probe the influence of these parameters on the photoelectrochem. characteristics. The highest incident photon-to-current conversion efficiencies of 90 and 30% for illumination through the conducting substrate and directly on the ZnO, resp., were obtained with a 8 μm thick ZnO film consisting of 150 nm spherical particles. For this system, no significant decrease in the photocurrent due to addn. of iodine or oxygen to the electrolyte was found. The electron losses from the conduction band of the ZnO electrodes are restricted to the zone of charge-carrier generation

Energy level alignment in TiO2/dipole-molecule/P3HT interfaces

Controlling the energy levels at the interface between an inorg. and an org. material is of importance to improve the properties in devices based on such hybrid interfaces, and can be obtained by the incorporation of dipole mols. between the materials. In this report interfaces contg. TiO2, a dipole mol. (benzoic acid or 4-nitrobenzoic acid) and a polymer, poly(3-hexylthiophene) (P3HT) were investigated using high kinetic energy photoelectron spectroscopy. The authors could successfully measure through all materials in the fully assembled systems, and thereby exptl. quantify the dipole induced change in the energy level alignment of the polymer and the TiO2

Determination of the electronic density of states at a nanostructured TiO2/Ru-dye/electrolyte interface by means of photoelectron spectroscopy

Photoelectron spectroscopy is used to measure the electronic d. of states in the band gap region of a nanostructured TiO2 film. Such nanostructured films are used in dye-sensitized solar cells, and a plain TiO2 film as well as a dye-sensitized film were examd. To simulate the electrolyte effect on the energy levels at the oxide/dye/electrolyte interface in a solar cell, the d. of states in the band gap region for an electrochem. prepd. TiO2 film inserted with Li+ was measured. The distribution and chem. nature of electron trap states in the band gap and the energy matching between the LUMO level of the adsorbed dye, cis-bis(4,4'-dicarboxy-2,2'-bipyridine)-bis(isothiocyanato)ruthenium(II), and the TiO2 conduction band edge are discussed

Spatial microheterogeneity in the valence band of mixed halide hybrid perovskite materials

The valence band of lead halide hybrid perovskites with a mixed I/Br composition is investigated using electronic structure calculations and complementarily probed with hard X-ray photoelectron spectroscopy. In the latter, we used high photon energies giving element sensitivity to the heavy lead and halide ions and we observe distinct trends in the valence band as a function of the I : Br ratio. Through electronic structure calculations, we show that the spectral trends with overall composition can be understood in terms of variations in the local environment of neighboring halide ions. From the computational model supported by the experimental evidence, a picture of the microheterogeneity in the valence band maximum emerges. The microheterogeneity in the valence band suggests that additional charge transport mechanisms might be active in lead mixed halide hybrid perovskites, which could be described in terms of percolation pathways

Electronic structure of electrochemically Li-inserted TiO2 studied with synchrotron radiation electron spectroscopies

The electronic properties were studied of TiO2 and electrochem. Li-inserted TiO2 using synchrotron radiation photoelectron spectroscopy and x-ray absorption spectroscopy (XAS) in conjunction with resonant photoelectron spectroscopy. Core level (Ti 2p) and valence level spectra show the presence of Ti3+ states in LixTiO2. The x values detd. from core level peak intensities were found to be directly correlated to the inserted amt. of Li+ detd. electrochem. The x-dependent width of the Ti 2p peaks is consistent with a two-phase regime at intermediate x values. Resonant photoelectron spectroscopy at the Ti 2p edge was performed for TiO2 and Li0.5TiO2 to delineate the Ti4+ and Ti3+ contributions to the XAS spectrum