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Organic solar cells based on Poly (3-hexylthiophene) [6,6]-phenyl C61-butyric acid methyl ester (P3HT-PCBM) were fabricated in standard architecture by spin-coating on glass and on flexible polyethylene terephthalate (PET) substrates in ambient laboratory environment. In addition to the conventional DC characterization, impedance spectroscopy was used in order to study the capacitive behavior of the devices and obtain their electrical parameters. In combination with the electrical characterization methods, laser-beam-induced current (LBIC) measurements were used as a non-destructive method of mapping the photocurrent distribution and analyzing local device failures and macroscopic defects (shunts, dark spots, defects). The results of the study can be used to develop guidelines for the development and design of P3HT:PCBM solar cells in ambient environment.

In this study, some crucial parameters were determined of flexible polymer–organic solar cells prepared from an active layer blend of poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) mixed in 1:1 mass ratio and deposited from chlorobenzene solution by spin-coating on poly(ethylene terephthalate) (PET)/ITO substrates. Additionally, the positive effect of an electron transport layer (ETL) prepared from zinc oxide nanoparticles (ZnO np) on flexible photovoltaic elements’ performance and stability was investigated. Test devices with above normal architecture and silver back electrodes deposed by magnetron sputtering were constructed under environmental conditions. They were characterized by current-voltage (I–V) measurements, quantum efficiency, impedance spectroscopy, surface morphology, and time–degradation experiments. The control over morphology of active layer thin film was achieved by post-deposition thermal treatment at temperatures of 110–120 °C, which led to optimization of device morphology and electrical parameters. The impedance spectroscopy results of flexible photovoltaic elements were fitted using two R||CPE circuits in series. Polymer–organic solar cells prepared on plastic substrates showed comparable current–voltage characteristics and structural properties but need further device stability improvement according to traditionally constructed cells on glass substrates.

Bulk heterojunction organic solar cells based on active layer of PTB7-Fx (x = 0–100), conjugated block copolymer incorporating benzo[1,2-b:4,5-b′]dithiophene and partly fluorinated thieno[3,4-b]thiophene units, and fullerene derivatives as phenyl C61 and phenyl C71 butyric acid methyl esters sandwiched between a transparent anode of indium tin oxide, a hole conducting layer of either poly(ethylene dioxythiophene) : polystyrene sulfonate or magnetron-sputtered molybdenum oxide and evaporated aluminum cathodes were fabricated. Polymer-organic thin films were prepared at 1:1.5 mass ratio of the donor:acceptor mixture and deposited from dichlorobenzene solution of different concentrations by spin coating in ambient conditions. To control the active layer morphology, the films were subjected either to post-deposition treatments (annealing) at different temperatures or incorporation of an additive such as diiodooctane. Optical transmission, film surface topography and thickness measurements were used to characterize the active layer. Test devices with the architecture described above were prepared and their current–voltage characteristics, quantum efficiency and impedance spectra were measured and used to compare the different active layers, architectures and deposition sequences.

ZnO has been widely used as electron selective material in P3HT:PCBM organic solar cells with either conventional or inverted architecture in order to enhance the extraction of electrons and block the collection of holes at one electrode. In this work we investigate the influence of ZnO nanoparticles electron transport layer (ETL) on the performance and stability of P3HT:PCBM based organic solar cells with conventional architecture and magnetron sputtered back Ag contacts. Their stability in the dark and under real outdoor conditions was monitored by current-voltage measurements and impedance spectroscopy. The impedance spectra were taken as a function of applied bias under illumination in order to reveal more information about the degradation mechanisms taking place in the device.

Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic system compared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges. © T. Abu Hamed et al., published by EDP Sciences, 2018., European Cooperation in Science and Technology: MP1406, The authors are grateful for the financial support by the COST Action MP1406 “MultiscaleSolar.”

LiFe1−xMnxPO4 solid solutions in the whole concentration range (0 ≤ x ≤ 1) are obtained at 500 °C by a phosphate–formate precursor method. The method is based on the formation of homogeneous lithium–iron–manganese phosphate–formate precursors by freeze-drying of aqueous solutions containing Li(I), Fe(II), Mn(II), phosphate, and formate ions. Thermal treatment of the phosphate–formate precursors at temperatures at 500 °C yields nano-sized LiFe1−xMnxPO4 coated with carbon. The structure and the morphology of the LiFe1−xMnxPO4 compositions are studied by XRD, IR spectroscopy, and SEM analysis. The in situ formed carbon is analyzed by Raman spectroscopy. The electrochemical performance of LiFe1−xMnxPO4 is tested in model lithium cells using a galvanostatic mode. All LiFe1−xMnxPO4 compositions are characterized with an ordered olivine-type structure with a homogeneous Fe2+ and Mn2+ distribution in the 4c olivine sites. The morphology of LiFe1−xMnxPO4 consists of plate-like aggregates which are covered by in situ formed carbon. Inside the aggregates nano-sized isometric particles with narrow particles size distribution (between 60 and 100 nm) are visible. The structure of the deposited carbon presents a considerable disordered graphitic phase and does not depend on the Fe-to-Mn ratio. The solid solutions LiFe1−xMnxPO4 deliver a good reversible capacity due to the Fe2+/Fe3+ and Mn2+/Mn3+ redox-couples at 3.5 and 4.1 V, respectively.

Wavelength converters have been proposed as one of the ways to achieve higher efficiency in third generation solar cells. The idea is to shift the wavelength of the light absorbed by the solar cell to the spectral region where the device is most efficient. Higher energy photons are often absorbed unproductively near the front contact of the solar cells. By the application of photoluminescent materials these photons are transformed into longer wavelength ones, which contribute more effectively to the generated photocurrent. In this study the improvement that a wavelength converter containing Tb3+ ions can produce on the efficiency of a thin film silicon single junction solar cell under AM 1.5 solar radiation is assessed by model calculations. The absorption and emission of a specified number of Tb3+ ions in a fluoride glass layer or plate is calculated on the basis of literature data. It is presumed that such a plate is placed in front of the solar cell and modifies the solar spectrum falling on the cell. This modified solar spectrum is used to calculate the efficiency of two model solar cells, an amorphous silicon and a microcrystalline silicon one, using the program Afors-Het 2.2. The amount of Tb3+ ions per unit area in the wavelength converter layer is varied. In the best case the efficiency of the a-Si:H solar cell improves by 1% and that of the microcrystalline silicon cell by 2.3%, in comparison to that calculated with the unmodified AM 1.5 spectrum.

This work demonstrates the possibility for low-temperature Liquid-Phase Epitaxy (LPE) growth of lattice matched to GaAs substrate dilute nitride InGaAsN layers with good crystalline quality and high Hall electron mobility. X-ray microanalysis and X-ray diffraction methods have been used to determine the composition and crystalline quality of the grown InGaAsN layers. Surface roughness is examined by atomic force microscopy. N-related local vibration modes are observed by Raman scattering. The Hall electron mobility and free carrier concentration have been measured in the temperature range 80-300K by conventional Van der Pauw method.

This work reports the results from the synthesis of nanostructured ZnO thin films via electrochemical deposition on glass substrates coated with F doped SnO2. The influence of the deposition parameters on the properties of the obtained ZnO films was studied. The Raman spectra of the ZnO films contain the typical for ZnO vibrational bands. The scanning electron microscope micrographs demonstrate that the films consist of ZnO nanowires. Growing of ZnO in the conditions with addition of H2O2 in lower concentration and without flowing air results in larger grain formation. The ZnO layers demonstrate high diffuse reflection.

International audience; Sodium manganates with nominal composition Na2/3MnO2 were prepared by solid state reaction between Na2CO3 and MnCO3 at 1000 °C. The composition and structure of NaxMnO2 were controlled by the rate of cooling from the temperature of preparation. This is a consequence of the capability of Na2/3MnO2 to accommodate over-stoichiometric Mn4+ ions up to 12.5%. Structural characterization was carried out by XRD powder diffractions, TEM analysis and Raman spectroscopy. The composition and oxidation state of manganese were determined by chemical analysis and magnetic susceptibility measurements. The manganese distribution in the layers was analysed using electron paramagnetic resonance (EPR) spectroscopy. By quenching from 1000 °C, the orthorhombic distorted modification is stabilized. A phase separation into orthorhombic and hexagonal modifications takes place when Na2/3MnO2 is slow cooled. The structure changes are concomitant with an increase in the oxidation state of Mn. The over-stoichiometric Mn4+ ions are accommodated in the hexagonal modification by creation of vacancies in the MnO2-layers.

In this work, thin-film heterojunction is prepared using ZnO and poly-Si thin films and its I-V characteristics are presented. ZnO thin films have been applied for device engineering in different heterostructures, as well. In this work, the I-V characteristics of a thin-film heterostructure n-ZnO/poly-Si are studied. The ZnO polycrystalline films are deposited by RF sputtering in an atmosphere of Ar on the surface of a p-type poly-Si layer. The poly-Si films are prepared on glass substrate by the method of aluminum-induced crystallization (AIC) from precursor layers of Al and a-Si:H. The Al and a-Si:H precursor films are deposited by magnetron sputtering on glass substrate. The a-Si :H film precursors contain 9 at% hydrogen. The isothermal annealing of the structure glass/Al/a-Si:H is performed in forming gas (N 2 + 5%H 2 ) in the temperature range of 530-550 °C for 7 and 21 h. The properties of the films are studied by X-ray diffraction (XRD), optical microscopy, optical transmission and reflection, and Raman spectroscopy. The I-V characteristics of the thin-films heterostructure n-ZnO/ poly-Si show diode behavior and ideality factor of 2.95.The structure exhibits photosensitivity under illumination.

We studied the degradation of different types of bulk heterojunction devices, in which the materials comprising the active layer and/or the materials used for the back electrode are varied. The devices are deposited on ITO covered glass and have the structure PEDOT:PSS/BHJ/Me, where PEDOT:PSS is the hole transport layer, BHJ (bulk heterojunction) is the active layer comprising a polymer donor (e.g. PTB7, PCDTBT) and a fullerene derivative acceptor (e.g. PC60BM, PC70BM) deposited by spin coating, Me is the metal back contact, which is either Ag or Al deposited by magnetron sputtering or thermal evaporation. The device performance was monitored after storage in the dark at ambient conditions by following the evolution of the J-V curve over time. Results of real conditions outdoor degradation studies are also presented. The stability of the different solar cell structures studied is compared.

Thin films of poly-Si on low cost substrates such as glass are attractive for thin film solar cells and other large-area electronic devices. The controlled and reproducible preparation of polycrystalline silicon thin films by aluminium-induced crystallisation (AIC) needs optimization of both the process of crystallisation and the deposition conditions of the precursor silicon and aluminium layers. In this work, the influence of the hydrogen concentration in the precursor amorphous silicon layer and the deposition temperature of the aluminium layer on the structural properties of poly-Si thin films obtained by AIC of un-hydrogenated (a-Si) and hydrogenated amorphous silicon films (a-Si:H) are studied. Stacks of glass/a-Si:H/Al were prepared for performing the AIC process. The aluminium and amorphous silicon films are deposited by rf magnetron sputtering. The hydrogen concentration in the a-Si:H films is varied from 0 to 18 at.%. The substrate temperature during a-Si (a-Si:H) deposition is kept constant at 250 °C. The Al film is deposited on top of the a-Si (a-Si:H). The deposition temperature of the aluminium films (T S Al ) is varied from room temperature (RT) to 500 °C. The samples are isothermally annealed in air at T an = 530 °C for 7 h. The structural properties of the poly-Si films are studied by Raman spectroscopy and optical microscopy. The results indicate that the hydrogen concentration in the precursor a-Si:H is a very important parameter. It is also observed that T S Al influences the structural properties of the poly-Si films. It is found that films with better crystalline structure are obtained when the a-Si:H precursor layers contain 9 at.% hydrogen and the aluminium deposition temperature is about 350 °C.

Thin films of silica containing 0.15 at.% Eu and 3.5 to 7 at.% Na were prepared by sol–gel chemistry and annealed at 600 ° C in air, then submitted to ion–exchange treatments in NaNO3 : AgNO3 for studying the effect of the plasmon resonance of Ag nanoparticles on the excitation of Eu3+ ions. When excited at other wavelengths in the UV other than that corresponding to the 7F0–5L6 transitions of the Eu3+ ions, the yield of the 5D0–7F2 emission is increased by a factor of the order of 10 in films containing Ag particles with respect to that in non-exchanged films.

We have investigated the various types of instability phenomena in μc-Si:H solar cells prepared by HWCVD under conditions close to the transition to amorphous growth, resulting in compact material, and other cells containing a high crystalline volume fraction of material with a pronounced porosity. It was found that light-induced degradation is most pronounced for material with some amorphous volume fraction while highly crystalline material is stable under illumination. On the other hand, we have observed a strong degradation of the current–voltage (J–V) parameters after treatment in de-ionized water of the cells with highly crystalline i-layers, while cells with compact i-layer material show very little changes.

Thin films of silica containing silver nanoclusters have been deposited by magnetron co-sputtering followed by thermal annealing. Laser modification of the mean cluster size was performed using the fourth harmonic of a Nd:YAG laser with energies of between 35 and 125 mJ/cm2. The mean size of the clusters was estimated from the shape of the plasmon resonance band in the optical absorption spectra with the help of a computer simulation based on the Mie theory in static approximation. It was found that laser treatment with fluences above a certain threshold leads to a reduction of the mean size of the clusters and this reduction is greater for greater fluences. After a long treatment with the same fluence the effect saturates. The final mean size of the clusters after saturation depends only on the laser fluence and not on the initial mean cluster size. When lower laser fluences were used it was possible after laser annealing to return the mean cluster size to its initial value by thermal annealing. In this way by using a combination of laser treatment and thermal annealing a predetermined mean cluster size could be achieved. The mechanism of laser-induced cluster-size modification is discussed.

Thin films of high-quality polycrystalline silicon (poly Si) on different substrates are of interest for manufacturing thin film transistors, solar cells, and image sensors. In this study, we present the results of an investigation of poly Si films on glass, formed by nickel-induced crystallization. The process is based on isothermal annealing in air at 550 and 560 °C of co-sputtered Ni+Si films deposited on glass at different substrate temperatures, with and without the application of an electric field to the films. The poly Si films were investigated by Raman spectroscopy and Rutherford back-scattering. It was established that the substrate temperature and the Ni-concentration in the precursor amorphous Si+Ni films are important parameters for nickel-induced crystallization.

The formation of high-quality polycrystalline silicon (poly-Si) on low cost substrates has important applications in the development of thin film solar cells, transistors, image sensors, etc. In this study, we present the results of an investigation of poly-Si and poly-SiGe films on glass, formed by aluminum induced crystallization (AIC). The process is based on the isothermal annealing at temperatures between 500 and 540 °C of co-sputtered Si+Al, Si+Ge or sputtered a-Si films on glass, with and without thermally evaporated or sputtered Al film. The crystallized films were investigated by Raman spectroscopy, optical microscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Raman spectra demonstrate the crystalline structure of the poly-Si and poly-SiGe films prepared by AIC. The grain sizes of the poly-Si films estimated from the SEM and optical microscopy images are up to 25 μm for the different annealing conditions.

Thin films (d∼200 nm) of hydrogenated amorphous silicon carbide (a-SiC:H), deposited by RF reactive magnetron sputtering, have been ion implanted with high doses (D=1016–1017 cm−2) of Ga+ as the implant species. The increased disorder and additional structural modification of a-SiC:H, induced by the implantation of Ga+, results in a considerable change of the optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies in the results obtained by optical transmission and reflection measurements and as derived from photo-thermal-deflection spectroscopy results. This shift may be attributed both to additional defect introduction and to accompanying structural modification effects, as confirmed by optical absorption measurements in the infra-red region and by Raman spectroscopy results.

The sensitization of the infrared luminescence of Er ions by Si clusters is studied in oxide films derived from tetraethoxysilane and triethoxysilane gels, doped chemically or by ion implantation with Er and/or Si. No quenching of the luminescence by impurities and structural defects is observed with respect to ion-implanted silica, and a maximum enhancement is observed in the SiO1.5 suboxide formed from triethoxysilane. The segregation of erbium silicide or oxide, depending on the synthesis procedure, deactivates the Er ions when their concentration exceeds 1 at % or the temperature of annealing is above 1050 °C.

The transformations induced by ion irradiation in films of polycarbosilane and gels derived from tetraethoxysilane, methyltriethoxysilane and triethoxysilane have been studied. Hydrogen is released selectively under the effect of electronic excitations at a rate depending on the probability of H radicals to combine for forming molecules inside the film. The radiolysis efficiency of C—H bonds is the lowest and that of Si—H bonds the highest. Beside the conversion of the polymeric structure into an amorphous ceramic, ion irradiation induces the precipitation of C or Si clusters, according to the precursor, leading to a noticeable luminescence in the visible. This precipitation has been put into evidence for the first time by energy filtered electron microscopy.

a-Si 1− x C x :H thin films doped with different concentrations of Tb have been deposited by magnetron co-sputtering. The carbon content in the films is varied in order to change the optical gap. RBS analysis shows that Tb is homogeneously distributed in the bulk. Optical absorption spectra in the visible are studied and changes in the optical gap and the defect absorption with increasing Tb concentration are observed. The laser excited photoluminescence (PL) of the films is studied after annealing at 300°C in Ar atmosphere. It consists of a broad band covering the whole visible spectrum. The position of the PL band does not change when the carbon content in the films is increased from 10 to 25 at%. It is tentatively assigned to the Tb 3+ impurity.

Ag nanoclusters in a SiO2 matrix prepared by RF magnetron co-sputtering and subsequent irradiation with heavy 4.5 MeV Au+ ions were formed. The refractive index and optical absorption spectra of the films were studied. The method of the disappearing diffraction pattern was used for the refractive index determination. The refractive index enhances with increasing Ag concentration, as expected from the light scattering theory. SiO2:Ag thin films exhibit a plasmon resonance in the visible region. In the as-deposited films the Ag nanoclusters are less than 1 nm and are formed during the deposition. The intensity of the plasmon peak is low. After irradiation with 4.5 MeV Au+ ions the intensity of the peak increases and the peak becomes narrower. The TEM study shows that this is related to the change in the size of the Ag nanoclusters.

Precipitation of silver clusters in silica is achieved by different methods: ion implantation, ion beam mixing of superimposed layers and ion irradiation of films deposited by means of co-sputtering or sol-gel technique. Main features of the nanoparticles depending on the preparation method are investigated by TEM. The optical extinction resonance of these clusters is analysed in terms of sizes and interaction between the clusters on the basis of calculations. We found that resonances in sputtered and gel films with low metal concentrations are well described by plasmon polaritons in isolated clusters and calculations based on Mie theory allow the study of their growth under irradiation. This theory is not appropriate to describe the optical response of silver clusters in silica implanted with Ag concentrations higher than 5 at.% or in ion beam mixed films, because of the interaction between clusters. Using an effective medium model, it is demonstrated that the random dispersion of clusters in implantation films causes fluctuations and, on average, an increase of the clusters polarization. On the contrary, the particular arrangement of the clusters with a bimodal size distribution in ion beam mixed films induces a screening effect between the clusters of largest size.

The luminescence properties of erbium-doped silicon offer exciting potential applications in optoelectronics. Although the optical and structural properties of this material have been studied extensively, there have been no prior examinations of the transport properties. In this paper, results from photo-thermal deflection spectroscopy (PDS) and from the study of transient photocurrents (TPC) in rf sputtered a-Si:H films doped with different concentrations of Er are presented. It is shown that films with and without Er feature a broad distribution of localised states. Incorporation of Er does not significantly influence the concentration or energy distribution of shallow states, but increases the sub-gap optical absorption associated with deeper states. The transient photocurrent remains detectable to times of at least 0.1 s, without evidence of significant carrier losses by recombination. This suggests that the transport properties are adequate for electroluminescent device applications.

Thin amorphous and polycrystalline tungsten oxide films were prepared by chemical vapour deposition at atmospheric pressure from a metalorganic precursor - tungsten hexacarbonyl. The dependence of the structural and optical properties of tungsten oxide films on the technological conditions has been investigated by XRD, Raman spectroscopy and spectroscopic ellipsometry.

Porous silicon (PS) is studied by stepwise peeling of the surface layer to clarify the non-uniformity in the photoluminescence (PL) and correlate it with the in-depth chemical bonding and structure of the 30 μm thick layer. The PL intensity grows by an order of magnitude after the peeling off of the first 10 μm and decreases five times in the next 5 μm while the peak maximum position shifts from 730 to 800 nm. X-ray photoelectron spectroscopy (XPS) measurements show that Si–Si and Si–O bonds are present both on the surface and below, and the preferential oxidation state of silicon changes from 3+ and 4+ on the surface to 1+ and 2+ below 10 μm. Using Raman spectroscopy silicon nanocrystals are shown to exist. Their mean size can be estimated at about 3 nm. These results show that the strongest PL comes from a region in the PS layer where silicon nanocrystallites are surrounded by oxides with a low level of oxidation and not from the strongly oxidized surface layer.

Thin films of polysiloxanes and polycarbosilanes with various substituents were converted into SiOC and SiC ceramics by irradiation with ions of increasing masses. The transformation kinetics as a function of the ion dose was assessed by means of ion beam analyses (RBS, NRA, ERDA), compaction measurements, spectroscopies of infrared absorption and Raman scattering. The kinetics depends strongly on the linear density of electronic excitations. The formed radicals tend to react with the atmosphere after irradiations when this density is too low for permitting their combination into crosslinks. Part of the C atoms segregate into clusters with a noticeable degree of tetragonal hybridization, varying with the nature of side groups in the polymeric precursor. This precipitation affords to the films interesting properties: (1) a strong yellow photoluminescence, within a given range of ion doses where the quantum dots of C are not too coarse or too numerous; (2) at higher doses, a hardness reaching that of amorphous SiC and three times that of films converted by heat treatment at 1000–1200°C (as evidenced by nanoindentation tests); (3) a greatly improved thermochemical stability.

We have studied the photoluminescence (PL) of inorganic polymers submitted to irradiations with increasing fluences of energetic He, C or Au ions and correlated the changes in luminescence spectra to structural transformations, evidenced by means of ion beam analyses, Raman, FTIR and spectroscopic ellipsometry. The films exhibit a strong yellow emission when the energy transferred by the ions to electron shells of target atoms is within a given range of 20 to 60 eV/atom. For this optimal amount of ionizations, the precipitation of quantum dots made of free carbon becomes noticeable. The vanishing of the luminescence for larger energy transfers is attributed to the percolation or growth of these dots, combined with a subcritical depletion in the H content of the surrounding SiO 1.5 C x : H y matrix.

A method of preparation of thin (1000 A) porous silicon layers by chemical etching of c-Si in HF:HNO 3 :H 2 O=1:3:5 solution is reported wherein a thin Al film is deposited by evaporation on the silicon surface prior to etching. The method is characterized by no “incubation” period to the onset of the stain etching. The reaction between Al and HNO 3 produces the required holes for the very fast start of the chemical etching of Si. Using Al patterns deposited through a mask or prepared by photolithography it is possible to achieve selective formation of porous silicon. The porous silicon layers exhibit visible photoluminescence and when prepared on p-type c-Si and a shallow p–n c-Si homojunction the resulting heterostructures also display electroluminescence and photovoltaic properties. © 1997 Elsevier Science S.A.

A correlation between the photoluminescence, chemical bonds and structure of c-Si subjected to electrochemical and laser induced chemical etching has been obtained by X-ray photoelectron spectroscopy, IR spectroscopy and Raman scattering. Photoluminescence is very strongly related to the chemical bonding and depends on the Si, O and C content and the presence of different oxidized states of Si which are different for porous silicon prepared on Si substrates of different electrical resistivity. Porous silicon having Si oxidized states typical for Si suboxides exhibits very intensive photoluminescence. The influence of the doping level of c-Si on the process of electrochemical etching as well as the influence of the laser power on the process of stain etching are discussed.

The changes in the visible photoluminescence and Raman spectra of n-type porous silicon as a result of rapid thermal annealing and chemical treatment have been studied. Modification of the chemical bonds due to these treatments has been observed by X-ray photoemission spectroscopy. Our results show that the change in the luminescence spectra of porous silicon is related to the modification of the chemical bonds and that complexes such as the terminations in siloxene as well as silicate molecules play a role in determining the optical properties of this new photonic material. The surface containing siloxene-like bonding exhibits very intensive photoluminescence. The presence of silicates leads to a decrease in luminescence intensity and to the appearance of a weak high energy band in the photoluminescence spectra.

Luminescent a-Si:O:C layers were obtained by magnetron co-sputtering and annealing. The maximum photoluminescence intensity is comparable with that of porous silicon. The luminescence maximum is between 1.8 eV and 2.2 eV. X-ray photoelectron spectroscopy finds both CSi and CC bonding and maximum luminescence is obtained when the amount of the two kinds of bonding is comparable.

Thin films of molybdenum oxide were deposited by radio frequency (RF) magnetron sputtering in Ar from a MoO3 target at different deposition power on glass and silicon substrates. The thickness of the films was determined by profilometer measurements and by ellipsometry. The films were annealed in air at temperatures between 200 and 400°C in air. The optical transmission and reflection spectra were measured. The conductivity of the as deposited and annealed films was determined. The crystal structure was probed by Raman spectroscopy. The oxidation state of the surface was studied by X-ray photoelectron spectroscopy (XPS) spectroscopy. The deposition technique described above was used to experiment with MoOx as a hole transport layer (HTL) in polymer solar cells with bulk hetrojunction active layer, deposited by spin coating. The performance of these layers was compared with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), which is the standard material used in this role. The measured current-voltage characteristics of solar cells with the structure glass/ITO/HTL/Poly(3-hexyl)thiophene (P3HT):[6,6]-phenyl-C61- butyric acid methyl ester (PCBM)/Al demonstrate that the studied MoOx layer is a good HTL and leads to comparable characteristics to those with PEDOT:PSS. On the other hand the deposition by magnetron sputtering guarantees reliable and repeatable HTLs.

A solution based deposition method to form nano-sized thin films of molybdenum oxide suitable for photovoltaic device applications is presented. The samples were deposited by spin-coating from molybdenum metal organic precursor solution on soda lime glass substrates. The influence of the process parameters such as spinning regime and concentration of the precursor solutions on the thickness and morphology of the films were investigated. The thermal decomposition of the molybdenum precursor and oxide formation were investigated by differential scanning calorimetry and characteristic patterns showed transitions up to 300oC followed by a zone of stability. Optical spectroscopy measurements in the wavelength range from 300 to 1800 nm presented an increase in transparency when temperature of annealing was raised up to 400oC. Raman scattering analysis revealed the presence of mixed molybdenum oxides. Measurements of the electrical conductivity were performed by the 4-point method.

Two types of polymer solar cells with active layers of P3HT:PCBM and PCDTBT:PCBM in a standard configuration were deposited by spin-coating the polymer layers and sputtering the Ag back contacts. After encapsulation, they were subjected to post-deposition annealing and were studied by measuring their current-voltage characteristics and quantum efficiency spectra. Their stability was examined by exposing them to solar radiation in open-circuit conditions for several hours every day for a total of 80 hours. Their characteristics were measured regularly throughout this period. The performance of the two types of cells are compared and discussed.

We report on the photoluminescence (PL) spectra of porous silicon excited resonantly by laser lines within the luminescence band. Measurements have been performed for different excitation energies, temperatures and delay times. At low temperatures, the known step-like phonon structure in the PL spectra of porous silicon and a gap of the few millielectronvolts between the laser line and the onset of the luminescence are observed. As the temperature is increased, the onsets of both the PL spectra and the step features shift towards higher energies whereas the peak of the spectrum moves towards lower energies by an amount which depends on the delay time after excitation. Furthermore, the gap disappears and simultaneously an exponential tail of the spectrum occurs on the high energy side of the laser line, which broadens proportionally to kT . These results are discussed in light of the existing theories for the luminescence mechanism in porous silicon and for the origin of the step features in the PL spectra.

Luminescence from stain-etched and electrochemically etched germanium samples was observed in the blue part of the visible spectrum. Although it is weaker than the luminescence of porous silicon, its origin is of scientific interest as a parallel to the luminescence of porous silicon. Stain-etched germanium was studied in more detail. Under visible laser excitation the luminescence band is located around 525 nm. Another luminescence band around 400 nm is observed with UV excitation. The luminescence lifetime in the UV-excited band is of the order of 1 ms, compared with about 100 ns in the band excited in the visible. The luminescence intensity either passes through a maximum or slowly decreases as the temperature is increased from 8 to 300 K. This behaviour is similar to that observed in porous silicon. The IR spectra of stain-etched Ge show the presence of GeO2, -OH groups and water. In the Raman spectra the unmistakable bands of trigonal crystal GeO2 are observed. A band at 760 cm−1 in the Raman spectra and 752 cm−1 in the IR spectra could be assigned to substoichiometric regions and oxygen-vacancy complexes in GeO2. The chemical composition of the samples is characterized by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The XP spectra give evidence for GeO2 and GeO. SIMS data show the presence of both hydrogen and -OH groups. On the basis of these data we propose that the luminescence of stain-etched and electrochemically etched germanium is due to defects in GeO2.

Thin films of tin sulfide (SnS) were prepared by thermal evaporation technique on glass substrates and on n-type Si substrate and their physical properties were studied. The phase of the obtained thin films before and after thermal treatment was confirmed by X-ray diffraction analysis and Raman spectra. Optical transmission and reflection spectra were measured in the wavelength range 300-1800 nm, and the data were used to determine the direct and indirect optical band gaps. Four-point measurements have revealed that SnS thin film exhibits p-type conduction. Current-voltage characteristics of the SnS/ n-Si structures demonstrate strong photosensitivity and photovoltaic effect. However, in order to be able to evaluate the potential applicability of this heterojunction for photovoltaic or electronic devices, further study and technological optimization has to be conducted.

International audience; In this contribution, new data on the reversible Li+ intercalation in iron substituted sodium manganates are provided. Novel Na2/3Mn1−yFeyO2 (y = 0, 1/3 and 2/3) compounds with a P′3-type structure are prepared from freeze-dried citrate precursors at 500 °C. A new structural element is the development of three-layer oxygen stacking contrary to the well-known P2-type Na2/3MnO2 with a two-layer sequence. The effect of Fe additives on the structure of Na2/3MnO2 was examined by XRD powder diffraction and TEM analysis. The oxidation state and the distribution of transition metal ions in Na2/3Mn1−yFeyO2 were analysed using electron paramagnetic resonance spectroscopy. The lithium intercalation in Na2/3Mn1−yFeyO2 was investigated in two-electrode lithium cells of the type Li|LiPF6 (EC:DMC)|Na2/3Mn1−yFeyO2. The stability of the layered phases during lithium intercalation was studied by ex situ Raman spectroscopy. It was found that the intermediate Na2/3Mn2/3Fe1/3O2 composition is able to intercalate Li+ reversibly in high amounts. Details of the structure and its stability during the Li+ intercalation are discussed.

An in situ optical microspectroscopy study of the surface plasmon resonance (SPR) evolution of Ag nanoparticles (NPs) embedded in thick SiO(2) films deposited on soda-lime glass has been conducted during thermal processing in air. The temperature and time dependences of the SPR were analyzed in the context of Mie extinction and crystal growth theories and were discussed along with consideration of oxidation processes and film/substrate physicochemical interactions. At relatively high temperatures, Ag NPs were indicated to grow first through a diffusion-based process and subsequently via Ostwald ripening. At lower temperatures, an initial decrease in Ag particle size was indicated due to oxidation, followed by NP diffusion-based growth. The growth and oxidation stages appeared temperature and time dependent, allowing for the tuning of material properties. The product of Ag NP oxidation was revealed by photoluminescence spectroscopy performed ex situ as single Ag(+) ions. The oxidative effect of the air atmosphere on Ag NPs was shown to be ultimately circumvented by the thick nanocomposite film. The phenomenon was explained on the basis of the displacement of the Ag/Ag(+) redox equilibrium toward Ag NP stability after ion migration toward the substrate being self-constrained. In addition, the current spectroscopic approach has been proposed for estimating the activation energy for silver diffusion in the SiO(2) matrix.

The structural properties of sodium manganates and iron substituted sodium manganates with compositions Na2/3Mn1-xFexO2 (x=0, 1/3 and 2/3) were studied by Raman spectroscopy. The Raman spectroscopy allows distinguishing between layered phases with orthorhombic (Cmcm space group) and hexagonal (P63/mmc space group) distortion. It has been found that the crystal structure and the composition of Na2/3MnO2 display a strong dependence on the history of the thermal treatment. The orthorhombic distorted modification is stabilized at high temperatures (1000 oC). At lower quenching temperature, there is a phase separation into an orthorhombic and a hexagonal modification, concomitant with an increase in the oxidation state of Mn. When Fe substitutes for Mn, the hexagonal modification is stabilized. In order to understand the origin of the Raman spectra of Na2/3Mn1-xFexO2, we have used Na2/3Co2/3Mn1/3O2 as a standard for hexagonal structure, where Co3+ and Mn4+ are statistically distributed in the transition metal layers.

The efficiency of thin film solar cells can be improved with the addition of a photon down-conversion top layer. This layer converts incident ultraviolet light of the solar spectrum to visible light, which transmits through the glass and is efficiently absorbed by the active layer of the solar cell. The results of our investigations of thin dielectric films and fluorozirconate glass, both doped with Tb3+ ions, are presented. Tb3+ has absorption bands between 250 and 380 nm; the corresponding emission bands are in the spectral range between 400 and 630 nm. Thin SiO2 and Al2O3 films with 0.04 - 10.18 at.% Tb were prepared by co-sputtering. For both as-deposited film systems, the highest fluorescence intensity is found for a Tb3+ doping level of approximately 1 at.%; the fluorescence intensity of Tb3+ in SiO2 is higher than that in Al2O3. Thermal treatment leads to an enhancement of the fluorescence intensity by more than one order of magnitude and the highest fluorescence intensity is found for 2 at.% Tb for annealed thin SiO2 films containing Tb3+. For comparison, the absorption and emission properties of Tb3+-doped fluorozirconate glass are investigated for a doping level of 0.3 at.% Tb.

ZnO has been extensively studied for many different applications, such as gas sensors, transparent conductive electrodes in solar cells and light emitting diodes, etc., because of its chemical stability and sensitivity to different adsorbed gases, amenability to doping, large energy gap, nontoxicity and low cost. ZnO thin films have been applied for device engineering in different heterostructures, as well. In this work the I‐V characteristics of two thin film heterostructures n‐ZnO/p‐poly‐Si with ZnO films with different thicknesses, 80 and 300 nm are studied. The ZnO polycrystalline films are deposited by RF sputtering in an atmosphere of Ar on the surface of a p‐type poly‐Si layer. The poly‐Si films are prepared on glass substrate by the method of Aluminum Induced Crystallization (AIC) from precursor layers of Al and a‐Si:H. The Al and a‐Si:H precursor films are deposited by magnetron sputtering on glass substrate. The a‐Si:H film precursors contain 9 at.% hydrogen. The isotermal annealing of the struc...

Thin transparent dielectric films containing Tb3+ are developed for application as spectral converters of the solar spectrum in thin film silicon solar cells. The results on the deposition and characterization of thin SiO2 and Al2O3 films containing Tb3+ ions are presented. The films are prepared by RF magnetron co‐sputtering, a well established technique for large area coatings. Photoluminescence (PL) is measured at room temperature, using the 488 nm line of an Ar laser and a nitrogen‐cooled CCD camera attached to a monochromator. The dependence of the PL intensity on the concentration of Tb in the film is studied. It is found that the intensity exhibits a maximum at about 1 at.%. Annealing studies are performed on SiO2:Tb with two different methods to improve the PL intensity. In both regimes of annealing, the best results for thin SiO2:Tb films are obtained in the temperature range of 650–700° C. After treatment at this temperature the Tb PL increases 2.5–3 times.

We describe in detail a very large nuptial flight of the antLeptothorax acervorum at an open hilltop site in Britain. The mating behaviour of these ants involved not only a large mating swarm but also sexual/calling behaviour by the females. The females left the flight to land on vertical objects, where they took up a characteristic calling posture, in which females of closely related species are known to release pheromones that are sexually attractive to males. ThatLeptothorax acervorum has a complex mating behaviour involving both large nuptial flights and sexual calling has important consequences for the interpretation of the evolution of polygyny in this species and social parasitism in its close relatives.

The laser excited luminescence of CaF2:Ho has been studied between 17 and 300 K using various Ar+ and He-Ne laser lines. The dependence of the effectiveness of excitation on the laser photon energy finds explanation if one-phonon assisted processes are taken into account. The adiabatic model and the model of phonon relaxation has been applied to the experimental linewidth temperature dependence of the A-sites of Ho3+ (transition 5F4, 5S2 to 5I7) and Er3+ (transition 4S3/2 to 4I15/2) and the results are discussed.