In situ syntheses of semiconducting nanoparticles in conjugated polymer matrices and their application in photovoltaics

Hybrid solar cells based on conjugated polymers and inorganic semiconducting nanoparticles combine beneficial properties of organic and inorganic semiconductors and are, therefore, an exciting alternative to pure organic or inorganic solar cell technologies. Several approaches for the fabrication of hybrid solar cells are already elaborated and explored. In the last years routes have emerged, where the nanoparticles are prepared directly in the matrix of the conjugated polymer. Here, the conjugated polymer prevents the nanoparticles from excessive growth and thereby makes additional capping agents obsolete. This review focuses on in situ preparation methods of inorganic semiconducting nanoparticles in conjugated polymers in view of applications in hybrid solar cells. The details, advantages and disadvantages of the different in situ methods are critically examined and put in comparison to the classical route where pre-synthesized nanoparticles are used. Various key factors influencing the solar cell performance as well as future strategies for increasing the overall efficiency of hybrid solar cells prepared via in situ routes are discussed

Polymer/Nanocrystal Hybrid Solar Cells: Influence of Molecular Precursor Design on Film Nanomorphology, Charge Generation and Device Performance

In this work, molecular tuning of metal xanthate precursors is shown to have a marked effect on the heterojunction morphology of hybrid poly(3-hexylthiophene-2,5-diyl) (P3HT)/CdS blends and, as a result, the photochemical processes and overall performance of in situ fabricated hybrid solar cells. A series of cadmium xanthate complexes is synthesized for use as in situ precursors to cadmium sulfide nanoparticles in hybrid P3HT/CdS solar cells. The formation of CdS domains is studied by simultaneous GIWAXS (grazing incidence wide-angle X-ray scattering) and GISAXS (grazing incidence small-angle X-ray scattering), revealing knowledge about crystal growth and the formation of different morphologies observed using TEM (transmission electron microscopy). These measurements show that there is a strong relationship between precursor structure and heterojunction nanomorphology. A combination of TAS (transient absorption spectroscopy) and photovoltaic device performance measurements is used to show the intricate balance required between charge photogeneration and percolated domains in order to effectively extract charges to maximize device power conversion efficiencies. This study presents a strong case for xanthate complexes as a useful route to designing optimal heterojunction morphologies for use in the emerging field of hybrid organic/inorganic solar cells, due to the fact that the nanomorphology can be tuned via careful design of these precursor materials

Further caries decline in Swiss recruits from 1996 to 2006

Swiss army recruits (N = 606) from the army base at Thun were dentally examined with a standardized method in the year 2006. The results were compared with those of previous surveys (1985 and 1996). The mean DM6FT-value in the year 2006 was 3.11, whereas in 1996 it had been clearly higher (4.95). This corresponds to a caries decline of 37%. The observed caries decline can only partly be explained. Recruits, who were smokers, showed an increased caries experience. Recruits of the German-speaking part of Switzerland who had profited from oral health lessons by oral health instructors in Kindergarten and primary schools did not differ in caries experience from recruits of the French-speaking part of Switzerland

Effect of thermal annealing on the structure and microstructure ofTiO2 thin films

Nanostructured TiO2 thin films have been prepared through chemical route using sol-gel and spin coating techniques. The deposited films were annealed in the temperature range 400–1000°C for 1 h. The structure and microstructure of the annealed films were characterized by GAXRD, micro-Raman spectroscopy and AFM. The as-deposited TiO2 thin films are found to be amorphous. Micro-Raman and GAXRD results confirm the presence of the anatase phase and absence of the rutile phase for films annealed up to 700°C. The diffraction pattern of the film annealed at 800 to 1000°C contains peaks of both anatase and rutile reflections. The intensity of all peaks in micro-Raman and GAXRD patterns increased and their width (FWHM) decreased with increasing annealing temperature, demonstrating the improvement in the crystallinity of the annealed films. Phase transformation at higher annealing temperature involves a competition among three events such as : grain growth of anatase phase, conversion of anatase to rutile and grain growth of rutile phase. AFM image of the as-deposited films and annealed films indicated exponential grain growth at higher temperature.Effect of thermal annealing on the structure and microstructure ofTiO2 thin films Haripriya Rath1*, S Anand2, M Mohapatra2, Priyadarshini Dash1, T Som3, U P Singh4 and N C Mishra1 1Department of Physics, Utkal University, Bhubaneswar-751 004, Orissa, India 2Institute of Minerals and Materials Technology, Bhubaneswar-751 013, Orissa, India 3Institute of Physics, Bhubaneswar-751 005, Orissa, India 4KIIT University, Bhubaneswar-751 024, Orissa, India E-mail : [email protected] of Physics, Utkal University, Bhubaneswar-751 004, Orissa, India 2Institute of Minerals and Materials Technology, Bhubaneswar-751 013, Orissa, India 3Institute of Physics, Bhubaneswar-751 005, Orissa, India 4KIIT University, Bhubaneswar-751 024, Orissa, India 1Department of Physics, Utkal University, Bhubaneswar-751 004, Orissa, India 2Institute of Minerals and Materials Technology, Bhubaneswar-751 013, Orissa, India 3Institute of Physics, Bhubaneswar-751 005, Orissa, India 4KIIT University, Bhubaneswar-751 024, Orissa, Indi

Exploring polymer/nanoparticle hybrid solar cells in tandem architecture

Tandem solar cells offer the possibility to significantly enhance solar cell performance through harvesting a broader part of the solar spectrum by using complementary absorbing materials. We report on tandem solar cells, with at least one polymer/nanoparticle hybrid layer as absorber material, in which the nanoparticles are prepared in situ by thermal decomposition of metal xanthates directly in the polymer matrix. In a first series, we investigated a hybrid-organic tandem solar cell, with a hybrid solar cell consisting of the silafluorene containing low band gap polymer PSiF-DBT and copper indium sulphide (CIS) nanoparticles as the bottom cell, and a low band gap polymer (PTB7)/fullerene derivative (PC61BM) organic solar cell as the top cell in order to study different recombination layers. Tandem devices with open circuit voltages nearly reaching the sum of the individual cells have been realised. The short circuit current is equal to the value of the hybrid single cell and a fill factor above 50% is obtained, leading to power conversion efficiencies of about 4.1%. Furthermore, the first results on hybrid-hybrid tandem solar cells consisting of two PSiF-DBT/CIS solar cells are presented. Although the preparation of these double hybrid devices is challenging because of the necessity of two thermal annealing steps, the resulting multilayer stack reveals smooth and homogeneous layers with sharp interfaces. The first working hybrid-hybrid tandem solar cells still exhibited 81% of the sum of the open circuit voltages of the single junction solar cells. © 2013 The Royal Society of Chemistry

Evaporative Cooling of a Guided Rubidium Atomic Beam

We report on our recent progress in the manipulation and cooling of a magnetically guided, high flux beam of $^{87}{\rm Rb}$ atoms. Typically $7\times 10^9$ atoms per second propagate in a magnetic guide providing a transverse gradient of 800 G/cm, with a temperature $\sim550$ $\mu$K, at an initial velocity of 90 cm/s. The atoms are subsequently slowed down to $\sim 60$ cm/s using an upward slope. The relatively high collision rate (5 s$^{-1}$) allows us to start forced evaporative cooling of the beam, leading to a reduction of the beam temperature by a factor of ~4, and a ten-fold increase of the on-axis phase-space density.Comment: 10 pages, 8 figure

Weiterer Kariesrückgang bei Schweizer Rekruten von 1996 bis 2006

Rekruten der Rekrutenschule Thun (N = 606) wurden im Jahr 2006 mit einer standardisierten Methode zahnmedizinisch untersucht. Die Resultate wurden mit denjenigen aus früheren Erhebungen (1985 und 1996) verglichen. Der DM6FT-Wert betrug im Jahr 2006 im Durchschnitt 3,11; im Jahr 1996 lag er noch deutlich höher (4,95). Dies entspricht einem Kariesrückgang von 37%. Der beobachtete Kariesrückgang konnte nur zum Teil erklärt werden. Rekruten, die rauchten, zeigten einen erhöhten Kariesbefall. Rekruten aus der Deutschschweiz, die in Kindergarten und Primarschule von Schulzahnpflege- Instruktorinnen betreut worden waren, unterschieden sich im Kariesbefall nicht von den Rekruten aus der Romandie

Tissue-selective expression of a conditionally-active ROCK2-estrogen receptor fusion protein

The serine/threonine kinases ROCK1 and ROCK2 are central mediators of actomyosin contractile force generation that act downstream of the RhoA small GTP-binding protein. As a result, they have key roles in regulating cell morphology and proliferation, and have been implicated in numerous pathological conditions and diseases including hypertension and cancer. Here we describe the generation of a gene-targeted mouse line that enables CRE-inducible expression of a conditionally-active fusion between the ROCK2 kinase domain and the hormone-binding domain of a mutated estrogen receptor (ROCK2:ER). This two-stage system of regulation allows for tissue-selective expression of the ROCK2:ER fusion protein, which then requires administration of estrogen analogues such as tamoxifen or 4-hydroxytamoxifen to elicit kinase activity. This conditional gain-of-function system was validated in multiple tissues by crossing with mice expressing CRE recombinase under the transcriptional control of cytokeratin14 (K14), murine mammary tumor virus (MMTV) or cytochrome P450 Cyp1A1 (Ah) promoters, driving appropriate expression in the epidermis, mammary or intestinal epithelia respectively. Given the interest in ROCK signaling in normal physiology and disease, this mouse line will facilitate research into the consequences of ROCK activation that could be used to complement conditional knockout models