The difficulty to infiltrate solid-state hole semiconductors within micron-thick porous titania films is one of the major limiting factors for the achievement of efficient solid-state dye-sensitized ...solar cells. It was already shown that through the ordered interconnected pores of an inverse opal, the large surface area of several microns thick titania film can be easily decorated with a dye and filled with a solid-state hole semiconductor. In this paper, we show that ordered inverse opal mesoporous thick films of TiO
2 with these characteristics can be obtained by using a slurry of monodispersed polystyrene spheres and a titania-lactate precursor deposited by the doctor blade technique. The mechanism of formation of the inverse opal is also discussed.
Silk fibroin (SF) is a natural biocompatible material that can be integrated in a variety of photonic systems and optoelectronics: i.e. organic lasing from dye-doped nano-structured silk film. In ...this context, biological incorporation of doping molecules into SF by means of feeding silk worms with dyes to their diet could be an innovative and eco-sustainable approach to obtain doped SF substrates, thus avoiding additional chemical processes and post-treatments of the protein solution. In the present work, we demonstrated that SF regenerated solutions and films containing rhodamine B (RhB) could be successfully obtained from the cocoons of Bombyx mori fed with a RhB-added diet (RhB-md-SF). Comparative analyses of optical and vibration characteristics of the RhB-md-SF solution and films with those of white SF blended with RhB (RhB-d-SF) revealed significant differences, suggesting that the silkworm's metabolism could be involved in the binding mechanism of SF with RhB. In conclusion, we observed that the doping diet is a promising method for the green fabrication of SF-based optically active materials, and it opens novel routes for silk-based biophotonics.
A novel approach to increase the efficiency of solid-state Gratzel solar cells is presented. Large surface, titania inverse opal films is prepared, and used in fabricating solid-state dye sensitised ...organic-inorganic hybrid Gratzel solar cells. The ordered interconnected cavities forming the microporous structure allow an easy and desired penetration of both the dye and the solid-state hole conductor material favouring the intimate contact of both these elements through the whole depth of the titania. These cells show much higher efficiency as compared to solid-state Gratzel cells prepared, in twin procedures, by conventional method using nanocrystalline TiO2 films.
The Raman spectra of the charge-ordered manganite Pr0.65Ca0.35MnO3 were studied as functions of temperature and excitation energy and compared to magnetic moment and electrical conductivity ...behaviors. Both the charge ordering ( T(co) approximately 225 K) and the antiferromagnetic transitions ( T(N) approximately 175 K) affect the spectral shape and intensity, indicating strong charge-lattice and spin-lattice couplings. Below T(co) a transition from dynamic Jahn-Teller distortions to a collective static distortion takes place. A change of the spectra is observed on increasing the excitation energy above 2.5 eV and it is attributed to a resonant polaron excitation.
Organic light-emitting diodes (OLEDs) are nowadays one of the most attractive devices based on organic semiconductors due to their successful application in the display technology. ...Electroluminescence in OLEDs is mainly governed by the fluorescence from excited singlet states, which have large transition probabilities providing the major radiative pathway. The “forbidden” triplet state emission can be activated by increasing spin–orbit coupling via dye doping. The singlet–triplet exciton formation statistics is usually given by 1:3 partition due to the quantum constrains.
Injection of carriers with finite spin polarisation should influence and modify the recombination statistics and can be used for tuning of the device efficiency. In this context, the development of a new class of electrodes able to guarantee both efficient charge and spin injection becomes of paramount importance. We show that strongly spin polarised colossal magnetoresistance manganite La
0.7Sr
0.3MnO
3 (LSMO) can successfully substitute conventional ITO electrodes in OLEDs. Highly transparent, metallic and ferromagnetic LSMO layers were used in combination with standard Al and spin polarised Co top electrodes. Electrical and optical characterisations of the OLEDs with spin polarised electrodes indicate the applicability of the new manganite electrodes for organic light-emitting devices.
Electroluminescence in organic semiconductors strongly depends on the relative population of singlet and triplet excitonic states, i.e. on the carrier spin statistics. In conventional organic ...light-emitting diodes (OLED) the optical emission is usually based on fluorescence from excited singlet states, while triplet states provide phosphorescent radiation. Radiative emission from singlet excitons has a very large transition probability providing the main radiative pathway. Quantum constraints determine the statistics of singlet–triplet exciton formation from charge recombination to a 1:3 partition. Controlling the spin statistics by injecting carriers with the desired spin polarisation would open the way to enhance a chosen electronic transition and therefore increase the device efficiency.
We show that spin polarised materials can successfully replace conventional electrodes in OLEDs. Electrical and optical characterisations of Alq
3/TPD based OLEDs for both normal and spin polarised electrodes are presented. Epitaxial thin films of the manganite La
0.7Sr
0.3MnO
3 were used as spin polarised hole injectors, while iron and cobalt films were used as spin polarised electron injectors. The results are a first step towards the fabrication of devices where the light emission can be tuned by controlling the spin injection.
Ferroelectric molecular compounds present great advantages for application in electronics because they combine high polarization values, comparable to those of inorganic materials, with the ...flexibility and low-cost properties of organic ones. However, some limitations to their applicability are related to the high crystallinity required to deploy ferroelectricity. In this article, highly ordered ferroelectric patterned thin films of diisopropylammonium bromide have been successfully fabricated by a lithographically controlled wetting technique. Confinement favors the self-organization of ferroelectric crystals, avoiding the formation of polymorphs and promoting the long-range orientation of crystallographic axes. Patterned structures present high stability, and the polarization can be switched to be arranged in stable domain pattern for application in devices.
We report on the growth of magnetite films directly on thin layers of organic semiconductors by means of an electron beam ablation method. The deposition was performed at room temperature in a ...reactive plasma atmosphere. Thin films show ferromagnetic (FM) hysteresis loops and coercive fields of hundreds of Oersted. Micro Raman analysis indicates no presence of spurious phases. The morphology of the magnetite film is strongly influenced by the morphology of the underlayer of the organic semiconductor. These results open the way for the application of magnetite thin films in the field of organic spintronics.
Thin films made of organic semiconductors (α-sexithiophene, PDAS and PBAS) have been printed and the impact on morphology studied by optical, atomic force and electron microscopy. Surfaces in contact ...with the stamp during printing undergo a change towards smoother and more ordered material at the macromolecular scale. Interdigitated nanoelectrodes to be used as source and drain in TFTs have been made and printed down to 100 nm. PDAS and PBAS can be printed at room temperature and preserve their printed feature provided they are cross-linked afterwards.
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