Temperature is one of the most specific external parameters that can accelerate the degradation rate in polymer:fullerene solar cells. To detect modifications of the active layer materials, electric ...noise spectroscopy is a sensitive experimental technique. A detailed characterization of the dc electric transport and voltage–noise properties shows how thermal ageing is detrimental for the investigated bulk heterojunction photovoltaic system. In particular, an increase of the energy barrier height at the interface between the metal contact and the blend, and a simultaneous decrease of the charge carrier zero-field mobility, evaluated through the analysis of the flicker noise component, are observed as a consequence of a thermal treatment. These effects can be related to morphological changes of the solar cell active layer and interface, and are revealed by monitoring the noise level.
•Temperature induced degradation in polymer solar cells detected by electric noise.•A noise peak is a precursor of solar cell breakdown.•Thermal stress induces a strong reduction of the electron mobility.•Flicker noise analysis allows computation of electron mobility.
Cosmic dust grains (CD) are part of the evolution of stars and planetary systems and pervade the interstellar medium. Thus, their spectral signature may be used to deduce the physical features of the ...observed astronomical objects or to study many physical and chemical processes in the interstellar medium. However, CD samples are available only from sample-and-return space missions. Thus, they are rare and not sufficient to be used to perform laboratory experiments of astrophysical interest, such as to produce reference spectra. In this contribution, we describe a new physical vapor deposition (PVD) technique that allows the production of amorphous samples with controlled chemical and morphological characteristics. In particular, this technique was developed to grow uniform or microstructured layers of Mg-Fe amorphous silicates (olivine or pyroxene) that are materials of wide interest for laboratory experiments. We discuss the first results that were achieved by applying this new synthesis method. The layers were studied by combining infrared spectroscopy, scanning electron microscopy, and X-ray spectroscopy. The X-ray microscopy was used for the first time to characterize the internal structure of the grains in these synthetic samples. Finally, future improvements of the technique and foreseen applications are discussed.
Simultaneous photon-beam position and intensity monitoring is becoming of increasing importance for new-generation synchrotron radiation sources and free-electron lasers (FEL). Thus, novel concepts ...of beam diagnostics are required in order to keep such beams under control. From this perspective diamond is a promising material for the production of semitransparent in situ photon beam monitors, which can withstand the high dose rates occurring in such radiation facilities. Here, we report on the development of freestanding, single-crystal chemical-vapor-deposited diamond detectors with segmented electrodes. Due to their direct, low-energy band gap, InGaAs quantum well devices operated at room temperature may also be used as fast detectors for photons ranging from visible to X-ray. These features are valuable in low-energy and time-resolved FEL applications. In particular, a novel segmented InGaAs/InAlAs device has been developed and will be discussed. Dedicated measurements carried out on both these devices at the Elettra Synchrotron show their capability to monitor the position and the intensity of the photon beam with bunch-by-bunch temporal performances. Furthermore, preliminary tests have been performed on diamond detectors at the Fermi FEL, extracting quantitative intensity and position information for 100-fs-wide FEL pulses with a photon energy of 28.8eV.
•Development and testing of two types of photon beam-position monitors are reported.•First type is based on freestanding, single-crystal CVD diamond detectors.•Second type is based on InGaAs/InAlAs quantum well dice grown by MBE.•Laser and synchrotron radiation tests show bunch-by-bunch monitoring capabilities.•Preliminary tests of diamond detectors with free-electron laser are also presented.
Diamond is one of the most promising materials for developing innovative electronic devices. Chemical vapour deposition (CVD) homoepitaxial growth allows the synthesis of high quality single crystal ...diamond plates. However, the use of these crystals for electronic applications is hampered by their small area (typically of the order of 10mm2). Large areas are desired to ensure efficient particle or radiation detection with pixelated devices. By growing a thick CVD layer it is possible to enlarge the initial area of the substrate by a factor of 2 since growth also occurs laterally from the substrate.
In this work, by using an X-ray collimated synchrotron radiation beam, the detection and charge collection properties of an enlarged CVD single-crystal diamond are used as a point-to-point probe to study the material quality. It was found that stress and dislocation density are correlated with the detection properties of the enlarged regions. The sensitivity of the device is affected by the vertical-to-lateral growth interface and the enlarged material quality seems to be correlated with the distance from this interface.
► An enlarged single crystal diamond plate has been grown by chemical vapour deposition. ► PL imaging and optical microscopy were used to locate dislocation rich areas. ► An X-ray detector has been fabricated using the enlarged CVD singe crystal diamond. ► The detector photoresponse has been probed point to point with a X-ray synchrotron beam. ► A correlation between signal dampening and dislocation rich zones has been observed.
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