Non-steady state operation of polymer/TiO2 photovoltaic devices

We present data on the initial period of operation of Gilch-route NMH-PPV/TiO2 composite solar cells (CSCs) which show that during this period the CSCs operate in a non-steady state regime. The behavior is complex and may include a gradual rise of the open circuit voltage (V-oc) and of the short-circuit current density (J(sc)) with time, a passage through a maximum of either or both parameters, and even a sign reversal. The mechanisms most probably contributing to the transient processes are: i) diffusion driven redistribution of charges resulting in the build up of a quasi steady state charge density profile across the device; ii) photo-doping resulting in a relatively slow increase of the average charge carrier concentration and consequently of the conductivity of the device. The latter is responsible for a strong decrease in V-oc, and is evidenced by the significant increase in dark current after device illumination

Nanocomposite titanium dioxide/polymer photovoltaic cells: effects of TiO2 microstructure, time and illumination power.

Nanocomposite titanium dioxide/polymer photovoltaic cells have been fabricated using poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEHPPV). Two different types of titanium dioxide were used, one synthesized using a sol-gel method, the other was a commercial paste. The crystal structure, porosity and absorption spectra of the titanium dioxide layers were measured, and the titanium dioxide synthesized using the sol-gel method had a much lower level of anatase. The photovoltaic properties of the ITO/TiO2/MEHPPV/Au cells, which were similar for both types of TiO2, were measured as a function of illumination power and compared with equivalent circuit models. A simple equivalent circuit model incorporating a diode, two resistances and a light induced current was inconsistent with the illumination - dependent data and was improved by adding an illumination dependent shunt resistance. A very long lived, photo-induced increase in dark current was observed, which could not be explained by a polymer degradation mechanism or an increase in temperature under illumination, but was more likely to be due to trapped charge

Genome-wide linkage analysis of 972 bipolar pedigrees using single-nucleotide polymorphisms.

Because of the high costs associated with ascertainment of families, most linkage studies of Bipolar I disorder (BPI) have used relatively small samples. Moreover, the genetic information content reported in most studies has been less than 0.6. Although microsatellite markers spaced every 10 cM typically extract most of the genetic information content for larger multiplex families, they can be less informative for smaller pedigrees especially for affected sib pair kindreds. For these reasons we collaborated to pool family resources and carried out higher density genotyping. Approximately 1100 pedigrees of European ancestry were initially selected for study and were genotyped by the Center for Inherited Disease Research using the Illumina Linkage Panel 12 set of 6090 single-nucleotide polymorphisms. Of the ~1100 families, 972 were informative for further analyses, and mean information content was 0.86 after pruning for linkage disequilibrium. The 972 kindreds include 2284 cases of BPI disorder, 498 individuals with bipolar II disorder (BPII) and 702 subjects with recurrent major depression. Three affection status models (ASMs) were considered: ASM1 (BPI and schizoaffective disorder, BP cases (SABP) only), ASM2 (ASM1 cases plus BPII) and ASM3 (ASM2 cases plus recurrent major depression). Both parametric and non-parametric linkage methods were carried out. The strongest findings occurred at 6q21 (non-parametric pairs LOD 3.4 for rs1046943 at 119 cM) and 9q21 (non-parametric pairs logarithm of odds (LOD) 3.4 for rs722642 at 78 cM) using only BPI and schizoaffective (SA), BP cases. Both results met genome-wide significant criteria, although neither was significant after correction for multiple analyses. We also inspected parametric scores for the larger multiplex families to identify possible rare susceptibility loci. In this analysis, we observed 59 parametric LODs of 2 or greater, many of which are likely to be close to maximum possible scores. Although some linkage findings may be false positives, the results could help prioritize the search for rare variants using whole exome or genome sequencing

A polygenic burden of rare disruptive mutations in schizophrenia.

Schizophrenia is a common disease with a complex aetiology, probably involving multiple and heterogeneous genetic factors. Here, by analysing the exome sequences of 2,536 schizophrenia cases and 2,543 controls, we demonstrate a polygenic burden primarily arising from rare (less than 1 in 10,000), disruptive mutations distributed across many genes. Particularly enriched gene sets include the voltage-gated calcium ion channel and the signalling complex formed by the activity-regulated cytoskeleton-associated scaffold protein (ARC) of the postsynaptic density, sets previously implicated by genome-wide association and copy-number variation studies. Similar to reports in autism, targets of the fragile X mental retardation protein (FMRP, product of FMR1) are enriched for case mutations. No individual gene-based test achieves significance after correction for multiple testing and we do not detect any alleles of moderately low frequency (approximately 0.5 to 1 per cent) and moderately large effect. Taken together, these data suggest that population-based exome sequencing can discover risk alleles and complements established gene-mapping paradigms in neuropsychiatric disease

NMDA receptors are selectively partitioned into complexes and supercomplexes during synapse maturation

How neuronal proteomes self-organize is poorly understood because of their inherent molecular and cellular complexity. Here, focusing on mammalian synapses we use blue-native PAGE and ‘gene-tagging’ of GluN1 to report the first biochemical purification of endogenous NMDA receptors (NMDARs) directly from adult mouse brain. We show that NMDARs partition between two discrete populations of receptor complexes and B1.5MDa supercomplexes. We tested the assembly mechanism with six mouse mutants, which indicates a tripartite requirement of GluN2B, PSD93 and PSD95 gate the incorporation of receptors into B1.5MDa supercomplexes, independent of either canonical PDZ-ligands or GluN2A. Supporting the essential role of GluN2B, quantitative gene-tagging revealed a fourfold molar excess of GluN2B over GluN2A in adult forebrain. NMDAR supercomplexes are assembled late in postnatal development and triggered by synapse maturation involving epigenetic and activity-dependent mechanisms. Finally, screening the quaternary organization of 60 native proteins identified numerous discrete supercomplexes that populate the mammalian synapse

Quantitative ATR-IR analysis of anisotropic polymer films: Extraction of optical constants

In a series of three papers we present the results of surface structure analysis of anisotropic polymer films using ATR-IR spectroscopy. In the first paper, the methodology for quantitative ATR-IR analysis of optically biaxial polymer films of orthorhombic symmetry is outlined, and results are presented of the first stage of the analysis - the extraction of the anisotropic optical constants of the films. Attention is drawn to the necessity that adequate sample/ATR-IR crystal contact is achieved in order to measure the correct reflectivity spectra of the sample/crystal interface and therefore obtain the correct (n, k) spectra of the analyzed film. The anisotropic absorption index spectra of PET and isotactic polypropylene films are presented in the 1800-670 and 1400-800 cm-1 range, respectively, along with the ATR-IR spectra from which the optical constants have been calculated. The extraction of all three principal absorption index spectra of PET films allowed us to examine the optical anisotropy of PET films formed by uniaxial-planar and biaxial drawing. The uniaxial-planar films are strongly optically biaxial, whereas the biaxially drawn films have similar properties in the film plane, which are very different from those along the film thickness direction. These differences in optical anisotropy are related to the difference in chain orientation induced during uniaxial-planar and biaxial deformation of PET films and to the anisotropy of the PET monomer unit

Quantitative ATR-IR analysis of anisotropic polymer films: Surface structure of commercial PET

A commercial PET film has been characterized using variable-angle ATR-IR spectroscopy to create a depth profile of the surface. The anisotropic optical constants (n, k) of the film were extracted from the reflectivity spectra assuming that the depth region probed at each angle of incidence is homogeneous. The refractive index n, absorption index k, and absorption coefficient K spectra of the film were then employed to calculate the trans / gauche content of PET and the extent of trans conformer orientation as a function of depth of penetration. The trans-PET content of the commercial film we analyzed changes from 78% at a depth of penetration of 0.4 μm to 61% at a depth of penetration of 1.1 μm. Results of the orientational analysis of the film are presented, and problems specific to ATR-IR spectroscopy in such analysis are also discussed. © 2005 American Chemical Society

Time evolution of photoconductivity in TiO2 electrodes fabricated by a sol gel method

We report here on the time evolution of photoconductivity under continuous illumination in nanocrystalline TiO2 samples prepared by a sol gel method, and also on the conductivity decay once the illumination is switched off. We observe strong dependence of the photoconductivity on the illumination intensity for both processes. It is found that the conductivity decay after high-intensity illumination is slower than after low-intensity illumination, and we have attempted to explain these experimental results using a model involving hole trapping-detrapping processes

Intensity-dependent relaxation of photoconductivity in nanocrystalline titania thin films

We have discovered that the initial rate of the post-illumination decay of photoconductivity in nanocrystalline Ti O2 depends on the intensity of the illumination. The phenomenon is described by hole detrapping processes affected by electrostatic interactions between the trapped holes, and screening of these interactions by free electrons. The analysis allows determination of both the electron concentration and the electron mobility. In our materials, the value of electron mobility μ ≈ 10-6 cm2 V-1 s-1, in good agreement with results obtained by other methods. © 2006 The American Physical Society