1,720,981 research outputs found
Excitation Density Dependence of Optical Oxygen Sensing in Poly(9,9-dioctylfluorene) Waveguides Showing Amplified Spontaneous Emission
Full text linkReversible oxygen induced emission quenching of both the Spontaneous Emission (SE) and the Amplified Spontaneous Emission (ASE) of poly(9,9-dioctylfluorene) waveguides is demonstrated. We show that ASE shows a stronger quenching than SE, up to about 6.2 times, but also a stronger decrease when the excitation density increases. We conclude that the fast increase of the ASE decay rate is the main process in determining the ASE detection sensitivity, limiting the potentiality of sensitivity improvement of ASE with respect to SE
Characterization by Confocal Laser Scanning Microscopy of the Phase Composition at Interfaces in Thick Films of Polymer Blends
Full text linkConfocal Laser Scanning Microscopy (CLSM) has been used as a fast, user-friendly, and noninvasive tool for characterizing
the phase composition differences at the substrate and air interfaces in thick films of polymer blends. A clearly different phase
composition at the blend/glass interface and at the blend/air interface has been detected. We show that PCBM preferentially
accumulates at the glass/blend interface, while P3HT preferentially accumulates at the blend/air interface, by comparing the
integrated signal intensity of the luminescence coming from both interfaces. Our results demonstrate that CLSM can be used
conveniently for the fast identification of a preferential phase segregation at interfaces in polymer blends. This is useful in the
research field on devices (like sensors or planar waveguides) that are based on very thick layers (thickness higher than 1 micron)
Organic lasers: fundamentals, developments, and applications
No full textIn the past 30 years, organic conjugated molecules received a lot of attention in research because of their unique combination of active properties typical of semiconductors and the technological appeal typical of plastic materials. Among the different applications proposed for organic materials, organic lasers are quickly approaching the performance required for application, while the research on novel active materials is still ongoing. The book presents the current state of the art of the understanding of the physics of optical gain in organic systems and provides a complete description of the most recent advances in organic lasers, including both the structures currently closest to application as well as the fascinating and unconventional systems. The chapters are written by authors with wide experience in the field. The book starts with the basic aspects of the optical gain process and then progressively introduces the most advanced research topics, discussing the state of the art of active material development and the physics and development of fascinating systems for organic lasers, such as random lasers and microcavities in strong coupling, and concludes with a description of the physics and technology of external cavity and distributed feedback lasers. The book is unique that it covers basic aspects, technological aspects, and systems still a subject of basic science research
Amplified Spontaneous Emission Optimization in Regioregular Poly(3-hexylthiophene) (rrP3HT):poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) Thin Films through Control of the Morphology
No full textThe maximization of the optical gain of organic active materials
is a crucial step in the development of organic lasers. In this paper we
demonstrate that the amplified spontaneous emission (ASE) of regio regularpoly(3-hexylthiophene) (rrP3HT):poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) thin films is strongly affected by the film morphology,
controlled by changing the solvent used for the spin-coating deposition. The
solvent variation results in ASE threshold changes of up to 8-fold due to the
variation in the uniformity of the two polymers mixing, determining the optical
gain, and the morphology uniformity, affecting the losses. Our results
demonstrate that the morphology optimization is a very important step in the
development of organic materials with high optical gai
Microscopic Investigation of the Excitons' Intermolecular Energy Migration in the β phase of Poly(9-9-Dioctyl Fluorene) by Confocal Laser Spectroscopy
Full text linkWe investigated, by confocal laser spectroscopy, the role of the microscopic morphology on the fluorescence spectra of poly(9,9-dioctylfluorene) (PF8) thin films self-doped by the PF8 β phase. We demonstrate the existence, on the micron scale, of different regions in the films, characterized by locally different fluorescence spectra. We show that the microscopic morphology irregularities lead to locally nonuniform β-phase density resulting in the switching on or off of the intermolecular energy migration within the β-phase excited-state distribution. This effect causes considerable local variation of the fluorescence spectra consisting of a progressive red shift (up to 26 meV) and a line width narrowing from about 70 (similar to the absorption one) down to 52 meV
On the homogeneity of the external quantum efficiency in a free OPV roll-to-roll flexible solar module
No full textWe present a microscopic characterization of an organic photovoltaic (OPV) module demonstrator, fabricated within the “freeOPV” project. The local properties of the module are discussed on different length scales, from the submicrometric to the centimeters one, inferring the module structure and the origin of the different contributions to the optical and photoelectrical spatial inhomogeneity. We show that the local external quantum efficiency (EQE) in the individual cells of the module exhibits typical variations within 6–8% of the peak value over about 0.4 mm2. Larger variations are observed when comparing different cells across the module surface, with differences in the EQE peak values up to 1.6 times. Our results suggest that the roll-to-roll OPV module performance can be further improved by optimizing the printing uniformity as well as the charge extraction efficiency of electrodes
On the correlation between morphology and Amplified Spontaneous Emission properties of a polymer: Polymer blend
Full text linkWe investigate the Amplified Spontaneous Emission (ASE) properties of a prototypical host-guest polymer polymer blend, namely poly(9,9-dioctylfluorene) (PF8) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) blend, with different concentration ratio. We show that the initial F8BT content increase causes an increase of the F8BT ASE threshold, even leading to ASE suppression for F8BT contents between 25% and 75%. ASE is then recovered upon further increase of the F8BT relative content. We demonstrate that the ASE properties of the PF8:F8BT are dominated by morphology effects, like submicrometric phase segregation, determining the net gain of the active waveguides
Study of the series resistance evolution in organic solar cells by use of the Lambert W function
No full textThe time evolution of the series resistance of bulk heterojunction solar cells realized and stored in inert atmosphere as well as in air has been monitored by fitting the experimental current vs. voltage characteristic to the analytical solution of the real diode equation obtained by means of the Lambert W function. The method allows to determine if and at what extent the standard one diode model can be used to acceptably describe the organic device in the field of a preliminary simple and fast evaluation of the series resistance evolution with time, without the need of complex and time consuming numerical fitting algorithms
South Italy local grapes cultivar as a source of natural sensitizers in Dye-sensitized Solar Cells
No full textWe show that anthocyanines extracted from 3 different local cultivar of grapes characteristic of the South Italian region named ''Salento'' can effectively act as nature-friendly and eco-sustainable sensitizers in Dye-sensitized Solar Cells (DSSC) type devices. The natural pigments have been extracted in a simple way by immersing both the whole fruits and the fruit epicarps in methanol and in an ultrasonic bath, without any further purification step. The measured open circuit voltage and the fill factors are among the best values reported in literature. We compare the effectiveness of the extraction process from fermented and from fresh grapes, showing that the devices realized starting from the fresh fruit epicarps perform slightly better than those realized starting from the fermented fruit. We correlate this behavior with an interaction of different dye molecules in the device
- …
