Alessia Le Donne

Optimized luminescence properties of Mn doped ZnS nanoparticles for photovoltaic applications

Mn2+ doped ZnS nanoparticles (ZnS:Mn2+ NPs) are non-toxic systems known for their attractive light emitting properties. This paper discusses the luminescence properties of ZnS:Mn2+ NPs prepared by wet chemical synthesis with the objective of using them as down-shifters. A modification of the incident solar spectrum inducing improved exploitation of the UV region was expected to increase the efficiency of single junction cells with an optimal absorber band gap around 1.1 eV. The potential of ZnS:Mn2+ NPs as down-shifters was therefore demonstrated on both Si and Cu(In,Ga)Se2 solar cells.

Luminescence of Dislocations and Oxide Precipitates in Si

The analysis of the photoluminescence (PL) spectra of a number of silicon samples plastically deformed or simply thermally annealed was used to understand the rol e of oxygen and oxygen precipitates on the PL emissions in the 0.8-1.0 eV range. The results of this analysis show that it is possible to discrim inate between emissions due to oxygen-associated centres and those due to dislocations. Furthermore, i t has been shown on a sample presenting only (dissociated) 60° dislocations that the 0.807 eV e mission is absent, demonstrating that it comes either from dislocation intersections or from scr ew segments. Finally, it has been suggested that the strain field associat ed to oxide precipitates might be responsible of both narrow and broad bands, systematically present in most of the samples examined, which are therefore interpreted as being due to carr ier confinement effects in localized quantum wells at silicon/silicon oxide interfaces of oxide precipitates.

Silicon Carbide for Alpha, Beta, Ion and Soft X-Ray High Performance Detectors

High performance SiC detectors for ionising radiation have been designed, manufactured and tested. Schottky junctions on low-doped epitaxial 4H-SiC with leakage current densities of few pA/cm2 at room temperature has been realised at this purpose. The epitaxial layer has been characterised at different dose of radiations in order to investigate the SiC radiation hardness. The response of the detectors to alpha and beta particle and to soft X-ray have been measured. High energy resolution and full charge collection efficiency have been successfully demonstrated.

Effect of high pressure isostatic annealing on oxygen segregation in Czochralski silicon

The effect of single-step annealing at 450, 650, and 1000 °C under gigapascal hydrostatic pressures on oxygen segregation from Czochralski silicon samples was investigated. It was shown that the effect of applied pressure on the oxygen segregation processes begins to be detectable at 650 °C and significant at 1000 °C. Not only was the effect of the applied pressure clearly evidenced, but also that of the dopants. In the first case the presence of a gap level associated to self-interstitial clusters could be argued, whereas in the second case both the oxide particles segregation and the dislocation formation were demonstrated to be enhanced by the pressure and by the type of doping. Furthermore, visible and ultraviolet photoluminescence emission at cryogenic temperatures were observed from silicon dioxide particles or from oxide nuclei contained in the silicon matrix.

A chemical deposition process for low-cost CZTS solar cell on flexible substrates

Cu2ZnSnS4 (CZTS) thin films and solar cells were successfully prepared using a new process based on spray pyrolysis technique. The main advantage of the proposed process is the avoiding of sulphurisation process at high temperature and in toxic gases like H2S. X-ray diffraction studies and Raman spectroscopy confirmed the formation of good-quality microcrystalline CZTS films in a tetragonal structure. Optical measurements showed that CZTS films have a direct band gap and high absorption coefficient (4 × 104 cm−1) as requested for solar cell application. CZTS solar cell prototypes deposited on low-cost flexible plastic substrates were prepared and tested.

On the nature of striations in n-type silicon solar cells

In n-type Czochralski silicon (Cz-Si) wafer, swirl shaped regions with low lifetime (known as striations) can cause degradation up to 1% absolute or even more in homojunction industrial solar cells. Nevertheless, the nature of the defects responsible for the occurrence of these striations is still unclear. In this work, n-type Cz-Si solar cell precursors cut from industrial size ingots with different feedstock quality and oxygen content were analyzed by microwave photo-conductance decay and photoluminescence in order to investigate the nature of such defects. The results demonstrate that the defects responsible for the occurrence of striations are oxide nanoprecipitates formed during the high temperature steps for the solar cell realization, due to the presence of grown-in oxygen nuclei.

Gallium In-Depth Profile in Bromine-Etched Copper–Indium–Galium–(Di)selenide (CIGS) Thin Films Inspected Using Raman Spectroscopy

In the thin film solar cells domain, copper indium galium (di)selenide (CIGS) is a material with well-established photovoltaic purpose. Here the presence of a suitable [Ga]/([Ga]+[In]) (GGI) in-depth profile has proved to play a key role in the performance of cells. The implementation of a routine method based on reliable but easily available experimental techniques is mandatory to obtain information on the GGI profile of any CIGS layer, in order to achieve high efficiency chalcogenide layers. In this vein, we here propose and systematically test a simple method for the GGI profile determination based on repeated bromine etching of CIGS thin films followed by Raman analysis of the A1 peak position. The reliability of the proposed approach is verified using a methodical comparison with energy-dispersive X-ray spectroscopy (EDS) analysis and secondary ion mass spectroscopy (SIMS) profiles, showing a good agreement with the GGI in-depth profiles determined using Raman analysis on bromine etched samples.

Random surface texturing of mc-Silicon for solar cells with picosecond lasers; a comparison between 1064 nm, 532 nm and 355 nm laser emission wavelengths

Multicrystalline Silicon was textured with picosecond laser. Different laser wavelengths (λ = 1064, 532, 355 nm) where compared regarding laser-induced damage. We found that λ = 355 nm picosecond radiation resulted in shallower defect-reach region.

Advances in structural characterization of thin film nanocrystalline silicon for photovoltaic applications

The knowledge and control of the structural and morphological properties of nanocrystalline silicon is a fundamental requisite for its proper application in photovoltaics. To this purpose, nanocrystalline silicon films grown by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD) technique on different kinds of substrates were submitted to a systematic characterization using Raman spectroscopy, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The results showed that the nature of the film substrate induces deep changes in the structural properties of the deposited films. The importance of a Raman in–depth analysis for an accurate determination of the sample structure has been also demonstrated.

Electrical and Optical Characterization of Electron Irradiated X Rays Detectors Based on 4H-SiC Epitaxial Layers

This paper is aimed to improve previous results dealing with irradiation experiments of epitaxial 4H-SiC Schottky diodes in view of their application as X ray detectors. To this purpose, we have carried out a thorough comparison of results concerning the degradation of minority carriers diffusion length (Ld) induced by irradiation with 8.2 MeV electrons with the type and density of irradiation-induced traps, determined by DLTS measurements as well as with the features of the corresponding photoluminescence bands.