Browsing by Author "Corregidor, V."
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- Assessment of dye distribution in sensitized solar cells by microprobe techniquesPublication . Barreiros, M. Alexandra; Corregidor, V.; Alves, L. C.; Guimarães, Fernanda; Mascarenhas, João; Torres, Erica; Brites, Maria JoãoDye sensitized solar cells (DSCs) have received considerable attention once this technology offers economic and environmental advantages over conventional photovoltaic (PV) devices. The PV performance of a DSC relies on the characteristics of its photoanode, which typically consists of a nanocrystalline porous TiO2 film, enabled with a large adsorptive surface area. Dye molecules that capture photons from light during device operation are attached to the film nanoparticles. The effective loading of the dye in the TiO2 electrode is of paramount relevance for controlling and optimizing solar cell parameters. Relatively few methods are known today for quantitative evaluation of the total dye adsorbed on the film. In this context, microprobe techniques come out as suitable tools to evaluate the dye surface distribution and depth profile in sensitized films. Electron Probe Microanalysis (EPMA) and Ion Beam Analytical (IBA) techniques using a micro-ion beam were used to quantify and to study the distribution of the Ru organometallic dye in TiO2 films, making use of the different penetration depth and beam sizes of each technique. Different 1D nanostructured TiO2 films were prepared, morphologically characterized by SEM, sensitized and analyzed by the referred techniques. Dye load evaluation in different TiO2 films by three different techniques (PIXE, RBS and EPMA/WDS) provided similar results of Ru/Ti mass fraction ratio. Moreover, it was possible to assess dye surface distribution and its depth profile, by means of Ru signal, and to visualize the dye distribution in sample cross-section through X-ray mapping by EPMA/EDS. PIXE maps of Ru and Ti indicated an homogeneous surface distribution. The assessment of Ru depth profile by RBS showed that some films have homogeneous Ru depth distribution while others present different Ru concentration in the top layer (2 lm thickness). These results are consistent with the EPMA/EDS maps obtained.
- Assessment of dye distribution in sensitized solar cells by microprobe techniques [Comunicação oral]Publication . Barreiros, M. Alexandra; Corregidor, V.; Alves, L. C.; Guimarães, Fernanda; Sequeira, S.; Mascarenhas, João; Torres, Erica; Brites, Maria JoãoDye sensitized solar cells (DSC’s) have received considerable attention once this technology offers economic and environmental advantages over conventional photovoltaic (PV) devices. A DSC photoanode typically consists of a nanocrystalline porous TiO2 film, endowed with a large adsorptive surface area. Dye molecules that capture photons during device operation are attached to the film nanoparticles. The effective loading of the dye in the TiO2 electrode is of paramount relevance for controlling and optimizing solar cell parameters. In particular, the cell shortcircuit current density (Jsc) is directly proportional to the light harvesting ability of the photoanode, which in turn is strictly dependent on the dye concentration on the TiO2 adsorptive surface. In addition, the dye adsorption behavior affects the cell open circuit voltage (Voc). Relatively few methods are known today for quantitative evaluation of the total dye adsorbed in the film. In this context microprobe techniques come out as suitable tools to evaluate the dye distribution and dye depth profile in sensitized films. Electron Probe Microanalysis (EPMA) and Ion Beam Analytical (IBA) techniques using a micro-ion beam were used to quantify and to study the distribution of the ruthenium organometallic (N719) dye in TiO2 films, making use of their different penetration depth and beam sizes. Two different types of films were prepared and sensitized, mesoporous nanoparticles and 1D nanostructured TiO2 films (about 4 ìm thickness). The high sensitive analytical techniques used allowed to assess dye surface distribution and depth profile, by means of Ru signal, despite the low concentration of this element. X-ray mapping by EPMA/WDS technique made possible to visualise the dye distribution in sample cross-section. PIXE maps of Ru and Ti indicated an homogeneous surface distribution. The assessment of ruthenium depth profile by RBS showed that some films have homogeneous Ru depth distribution while others presented up to half of the Ru concentration in the top layer (2 ìm thickness) when compared to the lower one. Dye load evaluation in different TiO2 films by two different techniques (ìPIXE and EPMA/WDS) provided similar results of Ru/Ti. The assessment of the dye distribution and quantification across an oxide semiconductor film by microprobe techniques can lead to a better understanding of the device performance.
- CdTe nano-structures for photovoltaic devicesPublication . Corregidor, V.; Alves, L. C.; Franco, N.; Barreiros, M. Alexandra; Sochinskii, N. V.; Alves, E.CdTe nano-structures with diameter of ∼100 nm and variable length (200–600 nm) were fabricated on glass substrates covered with conductive buffer layers such as NiCr, ZAO (ZnO:Al2O3 + Ta2O5) or TiPd alloys. The fabrication process consisted of the starting vapour deposition of metal catalyst dropped layer followed by the isothermal catalyst-prompted vapour growth of CdTe nano-structured layer of controllable shape and surface filling. The effect of buffer layers on the crystallographic orientation and thickness of CdTe nano-structured layers is investigated by means of IBA techniques, SEM and X-ray diffraction. It was shown that the formed CdTe nano-layers have a cubic structure, mainly oriented towards the [1 1 1] crystallographic direction, except for those grown on ZAO layer where the X-ray diffraction signal is very weak to be associated to any crystallographic form. The RBS spectra recorded on different areas of each sample type showed an almost constant thickness and SEM images revealed an homogeneous and dense distribution of the structures. It was also possible to study the first stage of the nano-structures grown on the Bi2Te3 seeds.
- Dye assessment in nanostructured TiO2 sensitized films by microprobe techniquesPublication . Barreiros, M. Alexandra; Mascarenhas, João; Corregidor, V.; Alves, L. C.; Guimarães, Fernanda; Torres, Erica; Brites, Maria João
- Dye assessment in nanostructured TiO2 sensitized films by microprobe techniques [Poster]Publication . Barreiros, M. Alexandra; Mascarenhas, João; Corregidor, V.; Alves, L. C.; Guimarães, Fernanda; Torres, Erica; Brites, Maria JoãoDye sensitized solar cells (DSCs) have received considerable attention once this technology offers economic and environmental advantages over conventional photovoltaic (PV) devices. The PV performance of a DSC relies on the characteristics of its photoanode, which typically consists of a nanocrystalline porous TiO2 film, enabled with a large adsorptive surface area. Dye molecules that capture photons from light during device operation are attached to the film nanoparticles. The effective loading of the dye in the TiO2 electrode is of utmost importance for controlling and optimizing solar cell parameters. Relatively few methods are known today for quantitative evaluation of the total dye adsorbed on the film. In this work, a new approach combining microprobe techniques namely, Ion Beam Analytical (IBA) techniques using a micro-ion beam (Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE)) and Electron Probe Micro-Analysis (EPMA) was carried out to assess dye distribution and depth profile in TiO2 films and the dye load based on Ru/Ti mass ratio. Different 1D nanostructured TiO2 films were prepared, morphologically characterised by SEM, sensitized and analysed by the referred techniques. Dye load evaluation in different TiO2 films by three different techniques (PIXE, RBS and EPMA/ wavelength dispersive spectrometry (WDS)) provided similar results of Ru/Ti mass fraction ratio. Moreover, it was possible to assess dye surface distribution and its depth profile, by means of Ru signal, and to visualise the dye distribution in sample cross-section through X-ray mapping by EPMA/ energy dispersive spectrometry (EDS). PIXE maps of Ru and Ti indicated an homogeneous surface distribution. The assessment of ruthenium depth profile by RBS showed that some films have homogeneous Ru depth distribution while others present different Ru concentration in the top layer (2 ìm thickness). These results are consistent with the EPMA/EDS maps obtained. EPMA (WDS and EDS) together with IBA techniques proved to be powerful tools for functional materials characterisation and provided very promising results in the study of nanostructured TiO2 sensitized films.
- In-Depth Inhomogeneities in CIGS Solar Cells: Identifying Regions for Performance Limitations by PIXE and EBSPublication . Corregidor, V.; Barreiros, M. Alexandra; Salomé, P.M.P.; Alves, L. C.ABSTRACT: When considering materials to be used as active layers in solar cells, an important required parameter is the proper knowledge of their elemental composition. It should be heavily controlled during growth in order to obtain the desired band gap and to decrease the recombination defects and then increase the solar cell electrical performance. Ion beam analytical (IBA) techniques and, in particular, particle-induced X-ray emission (PIXE) and elastic backscattering spectrometry (EBS) are quite suitable to determine the thickness and composition of such active layers. Furthermore, if these techniques are performed using a nuclear microprobe, lateral and in-depth inhomogeneities can be clearly observed from 2D maps. In many cases, composition variations can be detected from the classical 2D maps obtained from the PIXE spectra. In this work, it is shown how the in-depth variations can also be studied when considering 2D maps reconstructed from the EBS spectra. Such variations are derived from processing conditions and can be related to (i) composition, (ii) thickness, (iii) roughness, and (iv) other nontrivial issues. Examples obtained on Cu(In,Ga)Se-2-based cells are presented and discussed. Furthermore, the combination of IBA techniques such as PIXE and EBS is shown to be a competitive and alternative method to the more used and established techniques such as X-ray fluorescence for checking the average composition of the solar cell active layers or secondary ion mass spectroscopy for determination of the elemental depth profile.
- Microscopy techniques for dye distribution in DSCs nanocrystalline TiO2 filmsPublication . Barreiros, M. Alexandra; Sequeira, S.; Alves, L. C.; Corregidor, V.; Guimarães, Fernanda; Mascarenhas, João; Brites, Maria João
- Microscopy techniques for dye distribution in DSCs nanocrystalline TiO2 filmsPublication . Barreiros, M. Alexandra; Sequeira, S.; Alves, L. C.; Corregidor, V.; Guimarães, Fernanda; Mascarenhas, João; Brites, Maria JoãoCapture of sunlight has attracted an increasing interest in the scientific community and triggered the development of efficient and cheap photovoltaic devices. Amongst recent generation technologies for solar energy conversion, dye-sensitized solar cells (DSCs) show an optimal trade-off between high-conversion efficiency and low-cost manufacturing. For the last two decades, significant progress has been made and best energy conversion efficiency of the DSC at the laboratory scale has surpassed 12% [1]. A lot of work has focused on the enlargement of surface areas to enhance the amount of adsorbed dyes by reduction of nanoparticle sizes or utilization of novel structures. Nevertheless there remain some crucial details of DSC operation for which limited information is available, namely dye diffusion and adsorption, surface coverage and dye distribution throughout the nc-TiO2 film. Microprobe techniques can be powerful tools to evaluate the dye load, the dye distribution and dye depth profile in sensitized films. Electron Probe Microanalysis (EPMA) and Ion Beam Analytical (IBA) techniques using a micro-ion beam, namely micro-Particle Induced X-ray Emission ( PIXE) and Rutherford Backscattering Spectrometry (RBS), were used to quantify and to study the distribution of the ruthenium organometallic (N719) dye in TiO2 films, profiting from the different penetration depth and beam sizes of each technique. Two different types of films were prepared and sensitized, mesoporous nanoparticles and 1D nanostructured TiO2 films (figure 1). Despite the low concentration of Ru, the high sensitive analytical techniques used allowed to assess the Ru surface distribution and depth profile. Fig. 2 shows the PIXE maps of Ru and Ti indicating an homogeneous surface distribution. The same figure presents the RBS spectra obtained with a 2 MeV proton beam of the same sample showing that a good spectra fit is obtained considering only two sample layers: the first one with a 1.7 ìm thickness; the second one being the SiO2 substrate. The Ru RBS signal also shows that the dye has an homogeneous depth distribution. Due to the fine spatial resolution of the EPMA/WDS (Wavelength Dispersive Spectroscopy) technique it was possible to visualise the dye distribution in sample cross-section (with micrometer or submicrometer dimensions) as presented in Fig. 3 for the elemental mapping of a mesoporous nanoparticle TiO2 film. Dye load evaluation by two different techniques (ìPIXE and EPMA/WDS) provided similar results (Ru/Ti values around 0.5 %). The distribution analysis of the organometallic dye (N719) was done through ruthenium distribution via X-ray mapping. RBS was used to assess the ruthenium depth profile. This assessment can lead to a better understanding of the device performance.
- Nuclear microprobe: the tool to characterize new materials for energy conversion [Poster]Publication . Corregidor, V.; Alves, L. C.; Barreiros, M. Alexandra; Salomé, P.M.P.
- PIXE and RBS on CIGS solar cells to study the elemental distribution [Comunicação oral]Publication . Corregidor, V.; Salomé, P.M.P.; Barreiros, M. Alexandra; Alves, L. C.