Influence of dendronization on spectral diffusion and aggregation in conjugated polymers

Dendronization has previously been suggested as a means of controlling the level of intermolecular interactions in macromolecular and polymeric compounds. We therefore studied the spectral relaxation dynamics of dendronized and non- dendronized polyfluorenes at different temperatures. Dendronization strongly affects inhomogeneous spectral broadening, resulting in a blue-shift and broadening of the otherwise narrow vibronic progression of polyfluorene at low temperature. Using gated spectroscopy we are able to identify emissive keto defects on isolated chains of both dendronized and non-dendronized polymers, along with a strong aggregation band in the solid state. Surprisingly, the emission from chemical and structural defects is found to be stronger in the case of the dendronized material. The observation of aggregate emission in dendronized polyfluorenes suggests that aggregation in these materials does not occur through linear π-stacking, but rather through electronic interactions at point contacts between chains introduced by structural kinks along the backbone

Control of the molecular geometry and nanoscale morphology in perylene diimide based bulk heterojunctions enables an efficient non-fullerene organic solar cell

Herein we present the design of three perylene diimide (PDI) derivatives with different molecular geometries; namely the monomeric PDI1, the bay-linked PDI2 dimer, and the bay-linked PDI4 tetramer with a 9,9'-spirobifluorene core that are utilized as electron acceptors in non-fullerene organic solar cells (OSCs). In all cases the PTB7-Th polymer is used as the electron donor. Among the three PTB7-Th: PDI systems, the highest power conversion efficiency (PCE) is obtained by the PDI4-based OSC device that exhibits a maximum PCE = 6.44% followed by the PDI2-based (PCE = 5.32%) and PDI1-based (PCE = 2.48%) devices. The detailed study of the photoluminescence quenching, morphology and temperature-dependent charge transport properties of the three systems reveal that the highest PCE of PTB7-Th: PDI4 is a consequence of the three-dimensional (3D) molecular architecture of PDI4 that tunes energetic disorder in the PDI phase and contributes to the improvement of electron transport. Transient photovoltage characterization experiments further identify that the actual effect coming from the 3D molecular geometry of the PDI4 acceptor on PCE is the minimization of non-geminate charge recombination losses. This study provides updated guidelines for optimizing further the molecular structure of 3D small molecular electron acceptors that can be used in highly efficient non-fullerene OSCs.1121Nsciescopu

Up-conversion photoluminescence in polyfluorene doped with metal (II)-octaethyl porphyrins

The up-conversion photoluminescence (PL) in films of polyfluorene (PF) doped with metallated porphyrins is reported for the first time. The dependence of the up-conversion process on the pump laser intensity and wavelength, the central metal moiety of the dopants, and the temperature is presented. Up-conversion emission is observed at pump intensities as low as 2 kW cm(-2). Comparison of the PF integral PL intensities after laser excitation by 532, 543, and 405 nm enables the discussion of the energy-transfer mechanism and the efficiency of the process

A avaliação da aprendizagem na licenciatura em matemática: o que dizem documentos, professores e alunos?

Tese (doutorado) - Pontifícia Universidade Católica de São Paulo, Programa de Estudos Pós-Graduados em Educação Matemática, São Paulo, 2017.Este estudo investiga como vem sendo abordada a avaliação da aprendizagem em cursos de licenciatura, tanto como prática quanto como elemento curricular constituinte da formação docente. A pesquisa buscou investigar o que dizem documentos, professores e alunos sobre a avaliação da aprendizagem na licenciatura em matemática. A relevância do estudo reside na importância da avaliação como elemento central nos processos de ensino e de aprendizagem e no reduzido número de pesquisas sobre o tema. Os referenciais teóricos foram buscados em Fernandes, em Lopes e Silva e em Arredondo e Diago e complementados por Hoffmann e Luckesi. Numa abordagem qualitativa de pesquisa, foram analisados os projetos político-pedagógicos de cursos de licenciatura em matemática de cinco universidades federais, uma de cada região geográfica do país, bem como os planos de ensino dos componentes curriculares dessas licenciaturas, limitados aos disponibilizados pelas instituições. Foram também realizadas entrevistas semiestruturadas com 10 professores e 10 alunos de cada um desses cursos e com dois pesquisadores da área de avaliação da aprendizagem, num total de 102 participantes. Para tratamento dos dados, utilizaram-se elementos da análise de conteúdo, conforme descrita por Bardin. A análise dos dados evidenciou que: na organização de quatro das licenciaturas pesquisadas não há espaço reservado à avaliação da aprendizagem como componente curricular; o tema é tratado de forma superficial, tanto pelos professores formadores (o que também foi apontado pelos licenciandos entrevistados) quanto nos documentos consultados; um número inexpressivo de referências bibliográficas listadas nos documentos analisados versa sobre avaliação da aprendizagem; o desempenho dos licenciandos é avaliado quase sempre por meio de provas, listas de exercícios, trabalhos e seminários, revelando uma concepção de avaliação como mera verificação da aprendizagem; são os professores da área de Educação, de modo geral, que concebem e praticam uma avaliação da aprendizagem com características de avaliação formativa. Assim, este estudo levantou importantes elementos para reflexão e para eventuais mudanças das práticas de avaliação de professores formadores, visando dar maior destaque à avaliação da aprendizagem como elemento curricular constituinte da formação inicial do futuro professor de matemática da educação básica.Abstract : This study investigated how the assessment of learning is being focused in teaching certification programs, both as a practice and curricular element of teacher training. Content derived from documents and teachers and students interviewed on the assessment of learning in teaching certification in mathematics was investigated. The relevance of the study lies in the importance of assessment as a central element in the teaching and learning processes and in the current dearth of studies on the subject. The theoretical approaches for the study were based on Fernandes, Lopes and Silva, and Arredondo and Diago and complemented by Hoffmann and Luckesi. This qualitative study analyzed the political-pedagogic projects of teaching certification courses in mathematics of five federal universities, one from each geographic region of Brazil, along with the teaching plans for curriculum components of these courses, as provided by the institutions. Semi-structured interviews were also conducted involving 10 teachers and 10 students from each of the courses plus two researchers from the learning assessment area, giving a total of 102 participants. Data treatment was performed using elements of content analysis, as per Bardin, revealing that no space was dedicated to the assessment of learning as a curricular component in the structure of four of the teaching certification courses studied; the subject was only touched upon, both by teacher trainers (also cited by students interviewed) and in the documents consulted; scant bibliographic references listed in the documents analyzed addressed the assessment of learning; the performance of trainee teachers was only assessed based on exams, lists of exercises, studies, and seminars, evidencing a concept of assessment of mere checking of learning; generally, teachers from the education area conceive and practice the assessment of learning based on formative assessment. Therefore, this study yielded important elements for reflection and change in student assessment practices among trainee teachers, with a focus on the assessment of learning as a constituent element of the curriculum in the training of future teachers of mathematics in basic education

Gravure printing for three subsequent solar cell layers of inverted structures on flexible substrates

Inverted organic photovoltaic devices have been fabricated by gravure printing on a flexible substrate. In order to enable printing of multiple layers sequentially, a systematic study of wetting behaviour of each layer in the device is performed. Successful wetting of a hydrophobic P3HT:PCBM surface by a hydrophilic PEDOT:PSS ink is achieved with the addition of a surfactant/alcohol to the PEDOT:PSS ink and with oxygen plasma treatment. We are therefore able to print titanium oxide, poly(3-hexylthiophene) (P3HT) blended with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) and poly-3,4-ethylenedioxythiophene: poly(styrene sulphonic acid) (PEDOT:PSS). As result we get for three printed layers a 0.6% power conversion efficiency. © 2010 Elsevier B.V. All rights reserved

Enhanced operational stability of the up-conversion fluorescence in films of palladium-porphyrin end-capped poly(pentaphenylene)

Up-conversion photoluminescence in a blue-emitting polymer doped with porphyrin macrocycles has been investigated and the component distribution of this system has been optimised. Covalent binding of the porphyrins to the polymer was implemented to decrease the separation of the dopant and matrix molecules, as well as dopant aggregation. The result is an up-conversion process with highly enhanced efficiency and operational stability (see picture; I=intensity). (Graph Presented) © 2005 Wiley-VCH Verlag GmbH & Co. KGaA

Gravure Printing Inverted Organic Solar Cells: The Influence of Ink Properties on Film Quality and Device Performance

We investigate the relationship between processing parameters and the device performance of gravure printed organic solar cells. Ink viscosity, surface energy and surface roughness are studied to optimise the printing process. Surfactants, additives and surface modification by plasma cleaning are utilised to achieve homogeneous printing of multilayer OPV device architectures. It is found that use of high boiling point solvents with high solubilities leads to a desirable surface morphology. The use of a printed metal oxide electrode within the inverted structure leads to devices with lifetimes exceeding those of devices in standard structures without the need for encapsulation. © 2012 Elsevier B.V

Triplet–Triplet Annihilation-Induced Up-Converted Delayed Luminescence in Solid-State Organic Composites: Monitoring Low-Energy Photon Up-Conversion at Low Temperatures

Hitherto, the role of the enhanced intermolecular interactions and the effect of lowering the temperature on the process of triplet-triplet annihilation-induced up-converted delayed luminescence in solid-state composites systems have remained controversial. Here we address these issues by performing temperature-dependent time-integrated and time-gated luminescence spectroscopic studies on the model photon up-converting solid composite comprising the (2,3,7,8,12,13,17,18-octaethyl-porphyrinato) PtII (PtOEP) sensitizer, mixed with the blue-light emitting 9,10 diphenyl anthracene (DPA) activator. Atomic force microscopy imaging and photoluminescence (PL) spectra confirm that the strength of intermolecular interactions in the DPA:PtOEP system can be tuned by keeping the composite either in its binary or in its ternary form with the use of the optically inert matrix of polystyrene (PS). By diluting DPA:PtOEP in PS, the concentration of the DPA excimeric and the PtOEP triplet dimer quenching sites is reduced and the lifetime of the DPA up-converted PL signal is prolonged to the microsecond time scale. By lowering the temperature to 100 K, the DPA up-converted luminescence intensity increases by a factor of 3, and this is attributed to the increased energetic disorder of the DPA excited states in the PS:DPA:PtOEP ternary system. These findings provide useful guidelines for the fabrication of efficient solid-state photon up-converting organic layers. © 2014 American Chemical Society