Oligomer studies on polymer photovoltaics

Solar cells based on polymers are an attractive alternative to silicon-based photovoltaics, because of their low cost and processing advantages. To increase the efficiency of polymer solar cells, however polymers are required that absorb light also in the near infrared part of the solar cells. The research described in this thesis aims to address some fundamental questions related to these so-called small band gap polymers. The method followed consists of the synthesis of small molecular model systems and detailed investigation of their properties by a variety of spectroscopic and electrochemical methods. In chapter 2, oligomers consisting of two cyclopentadithiophenes and different acceptor units are described. These oligomers were synthesized to investigate the influence of the type of acceptor unit on the band gaps and energy levels of small band gap polymers. It was found that oligomers having thiophene-based acceptors generally have lower HOMO and LUMO levels than oligomers having benzene-based acceptors. This will ultimately lead to lower voltages when these acceptor systems are applied in solar cells. No clear correlation was found between the acceptor strength and the singlet–triplet splitting energy. Chapters 3 to 5 deal with several series of donor–acceptor oligomers consisting of thiophene and thieno[3,4-b]pyrazine moieties. The series described in chapter 3 consists of oligomers formed by one, two or three thienopyrazines end capped with thiophene units. The effect of increasing the chain length of the systems with one or two thienopyrazines in the acceptor block is described in chapters 4 and 5. The optical and electrochemical properties of the series are evaluated both experimentally and theoretically. It is found that the dependence of these properties on the chain length is identical in all series. In literature, a number of possible causes for the small band gaps in this kind of systems are given, e.g. donor–acceptor effects and induction of a quinoid structure in the polymer chain. In the work described in this thesis, it is concluded that the main cause for the small band gaps in these systems is none of the previously mentioned possibilities. Rather, the strong acceptor and donor character of thienopyrazine (usually only regarded as a strong acceptor), combined with strong interactions between the neighboring thienopyrazine units, explains the observed small band gaps. Besides light absorption, charge separation and recombination processes are of crucial importance to photovoltaic cells. A detailed study of these processes in small band gap oligomer – fullerene triads is described in chapters 6 and 7. Triads containing oligomers using the thienopyrazine unit, described in previous chapters, are presented in chapter 6. In these systems very fast charge separation takes place close to the Marcus optimal region, followed by fast recombination in the inverted regime. Because of the short lifetime of the charge separated state, no recombination into triplet states could be observed. Systems using the diketopyrrolopyrrole unit in the oligomer part of the triads are described in chapter 7. Charge separation in these systems takes place in the Marcus normal regime, followed by recombination in the inverted regime. As the energy of the charge separated state is higher in these systems than in systems using the thienopyrazine unit, the lifetime of this state is long enough to allow intersystem crossing to the triplet state. Clear evidence for triplet recombination was observed in these systems. In the last chapter, the use of diketopyrrolopyrrole containing oligomers as acceptor materials in solar cells is explored. Although diketopyrrolopyrrole-containing polymers are normally used as donor materials, acceptor behavior was also present and solar cells were prepared consisting of polythiophene as the donor material and the oligomers as acceptor materials. The best device shows a power conversion efficiency of 0.31% in simulated solar light, with a photon to electron conversion efficiency of ~10% up to 700 nm. The efficiency seems to be limited by the coarse morphology of the blend

Search for Gravitational Waves Associated with Gamma-Ray Bursts during the First Advanced LIGO Observing Run and Implications for the Origin of GRB 150906B

We present the results of the search for gravitational waves (GWs) associated with γ-ray bursts detected during the first observing run of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO). We find no evidence of a GW signal for any of the 41 γ-ray bursts for which LIGO data are available with sufficient duration. For all γ-ray bursts, we place lower bounds on the distance to the source using the optimistic assumption that GWs with an energy of were emitted within the – Hz band, and we find a median 90% confidence limit of 71 Mpc at 150 Hz. For the subset of 19 short/hard γ-ray bursts, we place lower bounds on distance with a median 90% confidence limit of 90 Mpc for binary neutron star (BNS) coalescences, and 150 and 139 Mpc for neutron star–black hole coalescences with spins aligned to the orbital angular momentum and in a generic configuration, respectively. These are the highest distance limits ever achieved by GW searches. We also discuss in detail the results of the search for GWs associated with GRB 150906B, an event that was localized by the InterPlanetary Network near the local galaxy NGC 3313, which is at a luminosity distance of Mpc (z = 0.0124). Assuming the γ-ray emission is beamed with a jet half-opening angle , we exclude a BNS and a neutron star–black hole in NGC 3313 as the progenitor of this event with confidence >99%. Further, we exclude such progenitors up to a distance of 102 Mpc and 170 Mpc, respectively.United States National Science Foundation (NSF)Science and Technology Facilities Council (STFC) of the United KingdomMax-Planck-Society (MPS)State of NiedersachsenAustralian Research CouncilItalian Istituto Nazionale di Fisica Nucleare (INFN)French Centre National de la Recherche Scientifique (CNRS)Netherlands Organisation for Scientific ResearchCouncil of Scientific and Industrial Research of IndiaScience & Engineering Research Board (SERB), IndiaMinistry of Human Resource Development, IndiaSpanish Ministerio de Economía y CompetitividadConselleria d’Economia i CompetitivitatConselleria d’Educació Cultura i Universitats of the Govern de les Illes BalearsNational Science Centre of PolandEuropean CommissionRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceHungarian Scientific Research Fund (OTKA)Lyon Institute of Origins (LIO)National Research Foundation of KoreaIndustry CanadaProvince of OntarioBrazilian Ministry of ScienceFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Russian Foundation for Basic ResearchLeverhulme TrustMinistry of Science and Technology (MOST)Kavli FoundationNASA/NNX15AU74GRFBR/15-02-00532-iRFBR/16-29-13009-ofi-

Tests of General Relativity with GW150914

The LIGO detection of GW150914 provides an unprecedented opportunity to study the two-body motion of a compact-object binary in the large-velocity, highly nonlinear regime, and to witness the final merger of the binary and the excitation of uniquely relativistic modes of the gravitational field. We carry out several investigations to determine whether GW150914 is consistent with a binary black-hole merger in general relativity. We find that the final remnant's mass and spin, as determined from the low-frequency (inspiral) and high-frequency (postinspiral) phases of the signal, are mutually consistent with the binary black-hole solution in general relativity. Furthermore, the data following the peak of GW150914 are consistent with the least-damped quasinormal mode inferred from the mass and spin of the remnant black hole. By using waveform models that allow for parametrized general-relativity violations during the inspiral and merger phases, we perform quantitative tests on the gravitational-wave phase in the dynamical regime and we determine the first empirical bounds on several high-order post-Newtonian coefficients. We constrain the graviton Compton wavelength, assuming that gravitons are dispersed in vacuum in the same way as particles with mass, obtaining a 90%-confidence lower bound of 1013 km. In conclusion, within our statistical uncertainties, we find no evidence for violations of general relativity in the genuinely strong-field regime of gravity. © 2016 The American Physical Societ

First targeted search for gravitational-wave bursts from core-collapse supernovae in data of first-generation laser interferometer detectors

We present results from a search for gravitational-wave bursts coincident with two core-collapse supernovae observed optically in 2007 and 2011. We employ data from the Laser Interferometer Gravitational-wave Observatory (LIGO), the Virgo gravitational-wave observatory, and the GEO 600 gravitational-wave observatory. The targeted core-collapse supernovae were selected on the basis of (1) proximity (within approximately 15 Mpc), (2) tightness of observational constraints on the time of core collapse that defines the gravitational-wave search window, and (3) coincident operation of at least two interferometers at the time of core collapse. We find no plausible gravitational-wave candidates. We present the probability of detecting signals from both astrophysically well-motivated and more speculative gravitational-wave emission mechanisms as a function of distance from Earth, and discuss the implications for the detection of gravitational waves from core-collapse supernovae by the upgraded Advanced LIGO and Virgo detectors. © 2016 The American Physical Societ

GW150914: First results from the search for binary black hole coalescence with Advanced LIGO

On September 14, 2015, at 09∶50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) simultaneously observed the binary black hole merger GW150914. We report the results of a matched-filter search using relativistic models of compact-object binaries that recovered GW150914 as the most significant event during the coincident observations between the two LIGO detectors from September 12 to October 20, 2015 GW150914 was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203000 years, equivalent to a significance greater than 5.1 σ. © 2016 The American Physical Societ

Comprehensive all-sky search for periodic gravitational waves in the sixth science run LIGO data

We report on a comprehensive all-sky search for periodic gravitational waves in the frequency band 100–1500 Hz and with a frequency time derivative in the range of [−1.18,+1.00]×10−8  Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our galaxy. This search uses the data from the initial LIGO sixth science run and covers a larger parameter space with respect to any past search. A Loosely Coherent detection pipeline was applied to follow up weak outliers in both Gaussian (95% recovery rate) and non-Gaussian (75% recovery rate) bands. No gravitational wave signals were observed, and upper limits were placed on their strength. Our smallest upper limit on worst-case (linearly polarized) strain amplitude h0 is 9.7×10−25 near 169 Hz, while at the high end of our frequency range we achieve a worst-case upper limit of 5.5×10−24. Both cases refer to all sky locations and entire range of frequency derivative values. © 2016 The American Physical Societ

Directly comparing GW150914 with numerical solutions of Einstein's equations for binary black hole coalescence

We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic models, because for all simulations—including sources with two independent, precessing spins—we perform comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all the quadrupolar and octopolar modes. Consistent with the posterior distributions reported by Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)] (at the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing simulations. Follow-up simulations performed using previously estimated binary parameters most resemble the data, even when all quadrupolar and octopolar modes are included. Comparisons including only the quadrupolar modes constrain the total redshifted mass Mz∈[64  M⊙−82  M⊙], mass ratio 1/q=m2/m1∈[0.6,1], and effective aligned spin χeff∈[−0.3,0.2], where χeff=(S1/m1+S2/m2)·L^/M. Including both quadrupolar and octopolar modes, we find the mass ratio is even more tightly constrained. Even accounting for precession, simulations with extreme mass ratios and effective spins are highly inconsistent with the data, at any mass. Several nonprecessing and precessing simulations with similar mass ratio and χeff are consistent with the data. Though correlated, the components’ spins (both in magnitude and directions) are not significantly constrained by the data: the data is consistent with simulations with component spin magnitudes a1,2 up to at least 0.8, with random orientations. Further detailed follow-up calculations are needed to determine if the data contain a weak imprint from transverse (precessing) spins. For nonprecessing binaries, interpolating between simulations, we reconstruct a posterior distribution consistent with previous results. The final black hole’s redshifted mass is consistent with Mf,z in the range 64.0  M⊙−73.5  M⊙ and the final black hole’s dimensionless spin parameter is consistent with af=0.62–0.73. As our approach invokes no intermediate approximations to general relativity and can strongly reject binaries whose radiation is inconsistent with the data, our analysis provides a valuable complement to Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)]. © 2016 The American Physical Societ

Search for transient gravitational waves in coincidence with short-duration radio transients during 2007-2013

We present an archival search for transient gravitational-wave bursts in coincidence with 27 single-pulse triggers from Green Bank Telescope pulsar surveys, using the LIGO, Virgo, and GEO interferometer network. We also discuss a check for gravitational-wave signals in coincidence with Parkes fast radio bursts using similar methods. Data analyzed in these searches were collected between 2007 and 2013. Possible sources of emission of both short-duration radio signals and transient gravitational-wave emission include starquakes on neutron stars, binary coalescence of neutron stars, and cosmic string cusps. While no evidence for gravitational-wave emission in coincidence with these radio transients was found, the current analysis serves as a prototype for similar future searches using more sensitive second-generation interferometers. © 2016 The American Physical Societ

Observing gravitational-wave transient GW150914 with minimal assumptions

The gravitational-wave signal GW150914 was first identified on September 14, 2015, by searches for short-duration gravitational-wave transients. These searches identify time-correlated transients in multiple detectors with minimal assumptions about the signal morphology, allowing them to be sensitive to gravitational waves emitted by a wide range of sources including binary black hole mergers. Over the observational period from September 12 to October 20, 2015, these transient searches were sensitive to binary black hole mergers similar to GW150914 to an average distance of ∼600  Mpc. In this paper, we describe the analyses that first detected GW150914 as well as the parameter estimation and waveform reconstruction techniques that initially identified GW150914 as the merger of two black holes. We find that the reconstructed waveform is consistent with the signal from a binary black hole merger with a chirp mass of ∼30  M⊙ and a total mass before merger of ∼70  M⊙ in the detector frame. © 2016 The American Physical Societ

GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs

We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1 Ma™ during the first and second observing runs of the advanced gravitational-wave detector network. During the first observing run (O1), from September 12, 2015 to January 19, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November 30, 2016 to August 25, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, four of which we report here for the first time: GW170729, GW170809, GW170818, and GW170823. For all significant gravitational-wave events, we provide estimates of the source properties. The detected binary black holes have total masses between 18.6-0.7+3.2 Mâ™ and 84.4-11.1+15.8 Mâ™ and range in distance between 320-110+120 and 2840-1360+1400 Mpc. No neutron star-black hole mergers were detected. In addition to highly significant gravitational-wave events, we also provide a list of marginal event candidates with an estimated false-alarm rate less than 1 per 30 days. From these results over the first two observing runs, which include approximately one gravitational-wave detection per 15 days of data searched, we infer merger rates at the 90% confidence intervals of 110-3840 Gpc-3 y-1 for binary neutron stars and 9.7-101 Gpc-3 y-1 for binary black holes assuming fixed population distributions and determine a neutron star-black hole merger rate 90% upper limit of 610 Gpc-3 y-1. © 2019 authors. Published by the American Physical Society