140 research outputs found
Novel Physical Vapor Deposition Approach to Hybrid Perovskites: Growth of MAPbI3 Thin Films by RF-Magnetron Sputtering
Solution-based methods represent the most widespread approach used to deposit
hybrid organic-inorganic perovskite films for low-cost but efficient solar
cells. However, solution-process techniques offer limited control over film
morphology and crystallinity, and most importantly do not allow sequential film
deposition to produce perovskite-perovskite heterostructures. Here the
successful deposition of CH3NH3PbI3 (MAPI) thin films by RF-magnetron
sputtering is reported, an industry-tested method to grow large area devices
with precisely controlled stoichiometry. MAPI films are grown starting from a
single-target made of CH3NH3I (MAI) and PbI2. Films are single-phase, with a
barely detectable content of unreacted PbI2, full surface coverage and
thickness ranging from less than 200 nm to more than 3 {\mu}m. Light absorption
and emission properties of the deposited films are comparable to as-grown
solution-processed MAPI films. The development of vapor-phase deposition
methods is of interest to advance perovskite photovoltaic devices with the
possibility of fabricating perovskite multijunction solar cells or multicolor
bright light-emitting devices in the whole visible spectrum
Stimulated and spontaneous four-wave mixing in silicon-on-insulator coupled photonic wire nano-cavities
We report on four-wave mixing in coupled photonic crystal nano-cavities on a
silicon-on-insulator platform. Three photonic wire cavities are side-coupled to
obtain three modes equally separated in energy. The structure is designed to be
self-filtering, and we show that the pump is rejected by almost two orders of
magnitudes. We study both the stimulated and the spontaneous four-wave mixing
processes: owing to the small modal volume, we find that signal and idler
photons are generated with a hundred-fold increase in efficiency as compared to
silicon micro-ring resonators
Demonstration of fluorescence enhancement: via Bloch surface waves in all-polymer multilayer structures
An all-polymer photonic structure constituted by a distributed Bragg reflector topped with an ultrathin fluorescent polymer film has been studied. A Bloch surface wave resonance has been exploited to improve pumping efficiency. A strongly polarization and angle dependent fluorescence signal is found with respect to the light pumping beam and the emitted wavelength. Matching the most favorable condition for the pump coupling and the collection geometry, the signal obtained from the structure appears to be two orders of magnitude larger than the one of the bare emitting film
Strong coupling between excitons in organic semiconductors and Bloch Surface Waves
We report on the strong coupling between the Bloch surface wave supported by
an inorganic multilayer structure and -aggregate excitons in an organic
semiconductor. The dispersion curves of the resulting polariton modes are
investigated by means of angle-resolved attenuated total reflection as well as
photoluminescence experiments. The measured Rabi splitting is 290 meV. These
results are in good agreement with those obtained from our theoretical model
2,5-Diisopropenylthiophene by Suzuki\u2013Miyaura cross-coupling reaction and its exploitation in inverse vulcanization: a case study
A novel thiophene derivative, namely 2,5-diisopropenylthiophene (DIT) was synthetized by Suzuki\u2013Miyaura
cross-coupling reaction (SMCCR). The influence of reaction parameters, such as temperature, solvent,
stoichiometry of reagents, role of the base and reaction medium were thoroughly discussed in view of
yield optimization and environmental impact minimization. Basic design of experiment (DoE) and
multiple linear regression (MLR) modeling methods were used to interpret the obtained results. DIT was
then employed as a comonomer in the copolymerization with waste elemental sulfur through a green
process, inverse vulcanization (IV), to obtain sulfur-rich polymers named inverse vulcanized polymers
(IVPs) possessing high refractive index (n z 1.8). The DIT comonomer was purposely designed to (i) favor
the IV process owing to the high reactivity of the isopropenyl functionalities and (ii) enhance the
refractive index of the ensuing IVPs owing to the presence of the sulfur atom itself and to the high
electronic polarizability of the p-conjugated thiophene ring. A series of random sulfur-rdiisopropenylthiophene (S-r-DIT) copolymers with sulfur content from 50 up to 90 wt% were
synthesized by varying the S/DIT feed ratio. Spectroscopic, thermal and optical characterizations of the
new IVPs were carried out to assess their main chemical\u2013physical feature
All-Polymer Photonic Microcavities Doped with Perylene Bisimide J-Aggregates
Thanks to exciting chemical and optical features, perylene bisimide (PBI) J-aggregates
are ideal candidates to be employed for high-performance plastic photonic devices.
However, they generally tend to form - stacked H-aggregates that are unsuitable for
implementation in polymer resonant cavities. In this work, we demonstrate the efficient
compatibilization of a tailored perylene bisimide forming robust J-aggregated
supramolecular polymers into amorphous polypropylene. The new nanocomposite was
then implemented into an all-polymer planar microcavity which provides strong and
directional spectral redistribution of the J-aggregate photoluminescence, owing to a
strong modification of the photonic states. A systematic analysis of the photoemitting
processes, including photoluminescence decay and quantum yields, shows that the
optical confinement in the polymeric microcavity does not introduce any additional nonradiative
de-excitation pathways to those already found in the J-aggregate
nanocomposite film and pave the way to PBI-based high-performance plastic photonic
devices
All-Polymer Microcavities for the Fluorescence Radiative Rate 2 Modification of a Diketopyrrolopyrrole Derivative
Controlling the radiative rate of emitters with 6 macromolecular photonic structures promises flexible devices with 7 enhanced performances that are easy to scale up. For instance, radiative rate enhancement empowers low-threshold lasers, while rate suppression affects recombination in photovoltaic and photochemical processes. However, claims of the Purcell effect with polymer structures are controversial, as the low dielectric contrast typical of suitable polymers is commonly not enough to provide the necessary confinement. Here we show all-polymer planar microcavities with photonic band gaps tuned to the photoluminescence of a diketopyrrolopyrrole derivative, which allows a change in the fluorescence lifetime. Radiative and nonradiative rates were disentangled systematically by measuring the external quantum efficiencies and comparing the planar microcavities with a series of references designed to exclude any extrinsic effects. For the first time, this analysis shows unambiguously the dye radiative emission rate variations obtained with macromolecular dielectric mirrors. When different0 waveguides, chemical environments, and effective refractive index effects in the structure were accounted for, the change in the radiative lifetime was assigned to the Purcell effect. This was possible through the exploitation of photonic structures made of polyvinylcarbazole as a high-index material and the perfluorinated Aquivion as a low-index one, which produced the largest dielectric contrast ever obtained in planar polymer cavities. This characteristic induces the high confinement of the radiation electric field within the cavity layer, causing a record intensity enhancement and the steering the radiative rate. Current limits and requirements to achieve the full control of radiative rates with polymer planar microcavities are also addressed
Results on MOVPE SiGeSn deposition for the monolithic integration of III-V and IV elements in multi-junction solar cells
Abstract In order to produce a step forward towards the monolithic integration of III-V and IV compounds in multijunction solar cells, a first assessment of SiGeSn deposition in a metal organic vapour phase epitaxy (MOVPE) chamber also used for III-V growth has been carried out. The study brings insights on several aspects of the MOVPE SiGeSn growth in order to get a better control of SiGeSn composition and to obtain epitaxial layers with improved morphology. In particular, it is shown that the gas source Si2H6 is more influenced by the growth temperature compared to GeH4 and SnCl4, moreover, its competition with SnCl4 makes it difficult to incorporate Si in SiGeSn, as SnCl4 partial pressure is increased. SiGeSn morphology is shown to be strongly dependent on temperature, As carry-over and growth rate. A new growth model is introduced in order to explain the importance of the adatom bond lengths in inhibiting tin segregation when SiGeSn is grown at relatively high growth temperatures (>480 °C). In order to investigate the photovoltaic behaviour of SiGeSn, a single-junction GaAs/InGaP/SiGeSn/Ge functional device has been manufactured and characterized by external quantum efficiency (EQE) and current-voltage measurements. The experimental and the simulated EQE show the higher absorption coefficient of SiGeSn with respect to Ge, which allows using SiGeSn layers with a thickness three times lower than Ge to produce the same photovoltaic current
Plasmonic Structures for Sensing and Emitting Devices
We report on the study of a plasmonic nanostructure that could be adopted as platform for emitting and sensing applications. Several devices have been prepared and characterized by atomic force microscopy (AFM) and Fourier transform micro-reflectance (FT- pR) techniques. In addition, a modelling via finite-difference time-domain (FDTD) simulations have been developed in order to interpret the morphological shape and the optical response of the considered structures. Until now, remarkable performances as surface plasmon resonance (SPR) based optical sensor have been founded. Moreover, we are performing preliminary trials in order to establish a coupling between photoluminescence (PL) features of suitable emitters with respect to the plasmonic resonances
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