EUPVSEC 2018

There are many characterization techniques available to evaluate the health of solar panels, such as I-V characterization, infrared thermography (IR), photoluminescence (PL) and electroluminescence (EL). EL imaging has become in recent years a powerful diagnostic tool to evaluate PV modules. EL images allow to detect several defects and degradation modes in the solar cells. The failures are observed as dark contrasted areas in the images. Broad dark regions can be detected even in a low resolution image, while a high resolution image is needed to detect some more specific problems such as cracks, multi-cracks or other line-shaped defects.PósterJunta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA081U16)Ministerio de Economía, Industria y Competitividad (Proyect ENE2014-56069-C4-4-R

Photoluminescence Imaging and LBIC Characterization of Defects in mc-Si Solar Cells

Today’s photovoltaic market is dominated by multicrystalline silicon (mc-Si) based solar cells with around 70% of worldwide production. In order to improve the quality of the Si material, a proper characterization of the electrical activity in mc-Si solar cells is essential. A full-wafer characterization technique such as photoluminescence imaging (PLi) provides a fast inspection of the wafer defects, though at the expense of the spatial resolution. On the other hand, a study of the defects at a microscopic scale can be achieved through the light-beam induced current technique. The combination of these macroscopic and microscopic resolution techniques allows a detailed study of the electrical activity of defects in mc-Si solar cells. In this work, upgraded metallurgical grade Si solar cells are studied using these two techniques.Ministerio de Economía, Industria y Competitividad (ENE2014-56069-C4-4-R)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. Project VA081U16

Defect characterization of UMG mc-Si solar cells using LBIC and luminescence imaging techniques

Upgraded metallurgical-grade silicon (UMG Si) solar cells with different ranges of efficiencies were characterized through electroluminescence imaging (ELi) and light-beam induced current (LBIC) measurements. The results showed a good correlation between the EL intensity and the efficiency of the solar cells. ELi images gave a bright contrast at the defects, grain boundaries and intragrain defects, and dark contrast inside the grain bodies. Metallic impurities are much more present in some cells due to the directional solidification of the Si ingot. Local short-circuit current mapping with LBIC measurements revealed a bright zone in the neighborhoods of the defects due to the depletion of impurities. Internal quantum efficiencies (IQE) and effective diffusion lengths (Leff) were calculated using different excitation wavelengths. High resolution LBIC measurements revealed micrometric clusters of impurities around intragrain defectsSpanish MINECO project, ref. ENE2014-56069-C4-4-R and “Junta de Castilla y León (Spain)” project number VA081U1

Electroluminescence Imaging and Light-Beam Induced Current as characterization techniques of Multi-Crystalline Si Solar Cells

There is an increasing demand for characterizing multicrystalline solar cells at different stages of its service life. Luminescence techniques, e.g. electroluminescence (EL) and photoluminescence (PL), have acquired a paramount interest in the last years. These techniques are used in imaging mode, allowing to take a luminescence picture at a full wafer/cell scale. This imaging approach is fast and sensitive, but has a low spatial resolution, which avoids a detailed analysis of the defect distribution, which can led to misinterpretations about critical parameters as the minority carrier diffusion length, or the internal and external quantum efficiencies. If one complements these techniques with high spatial resolution techniques, such as light beam induced current (LBIC), one can study the electrical activity of the defects at a micrometric scale, providing additional understanding about the role played by the defects in full wafer/cell luminescence images. The combination of the macroscopic and microscopic resolution scales is necessary for the analysis of the full luminescence images in mc-Si solar cells.Proyecto de Investigación ENE2014-56069-C4- 4-R (MCIN)Proyecto de Investigación ENE2017-89561-C4-3-R (MCIN)Proyecto de Investigación VA081U16 (Junta de Castilla y León

Daylight luminescence system for silicon solar panels based on a bias switching method

Among the many characterization techniques for solar panel testing, two, electroluminescence (EL) and photoluminescence (PL), can provide useful visual information about the presence of different types of cell defects. EL is performed outdoors by night in commercial solar plants due to the very weak luminescence emission compared to sunlight. PL faces the added difficulty of needing to find a large-area homogeneous light source to excite the modules. Since nighttime work poses many drawbacks and risks, a daylight outdoor EL/PL system would be useful for offering safe inspection of solar plants. We present daylight luminescence techniques based on a bias switching method, in which a pulsed luminescence signal is obtained by alternating the polarization state of the solar panels, synchronizing it with the luminescence image detection by an InGaAs camera. Fast switching and selecting an optimized exposure time are key to achieving high-quality images. The daylight luminescence method described herein allows both EL and PL luminescence images to be obtained, even under high solar irradiance conditions.Proyecto de Investigación ENE2014-56069-C4- 4-R (MCIN)Proyecto de Investigación ENE2017-89561-C4-3-R (MCIN)Proyecto de Investigación RTC-2017-6712-3 (MCIN)Proyecto IDI-20151194 (CDTI)Proyecto de Investigación VA081U16 (Junta de Castilla y León)Proyecto de Investigación VA283P18 (Junta de Castilla y León

Thermally activated site exchange and quantum exchange coupling processes in unsymmetrical trihydride osmium compounds

Reaction of the hexahydride complex OsH6(PiPr3)2 (1) with pyridine-2-thiol leads to the trihydride derivative OsH3{κ-N,κ-S-(2-Spy)}(PiPr3)2 (2). The structure of 2 has been determined by X-ray diffraction. The geometry around the osmium atom can be described as a distorted pentagonal bipyramid with the phosphine ligands occupying axial positions. The equatorial plane contains the pyridine-2-thiolato group, attached through a bite angle of 65.7(1)°, and the three hydride ligands. The theoretical structure determination of the model complex OsH3{κ-N,κ-S-(2-Spy)}(PH3)2 (2a) reveals that the hydride ligands form a triangle with sides of 1.623, 1.714, and 2.873 Å, respectively. A topological analysis of the electron density of 2a indicates that there is no significant electron density connecting the hydrogen atoms of the OsH3 unit. In solution, the hydride ligands of 2 undergo two different thermally activated site exchange processes, which involve the central hydride with each hydride ligand situated close to the donor atoms of the chelate group. The activation barriers of both processes are similar. Theoretical calculations suggest that the transition states have a cis-hydride−dihydrogen nature. In addition to the thermally activated exchange processes, complex 2 shows quantum exchange coupling between the central hydride and the one situated close to the sulfur atom of the pyridine-2-thiolato group. The reactions of 1 with l-valine and 2-hydroxypyridine afford OsH3{κ-N,κ-O-OC(O)CH[CH(CH3)2]NH2}(PiPr3)2 (3) and OsH3{κ-N,κ-O-(2-Opy)}(PiPr3)2 (4) respectively, which according to their spectroscopic data have a similar structure to that of 2. In solution, the hydride ligands of 3 and 4 also undergo two different thermally activated site exchange processes. However, they do not show quantum exchange coupling. The tetranuclear complexes [(PiPr3)2H3Os(μ-biim)M(TFB)]2 [M = Rh (5), Ir (6); H2biim = 2, 2‘-biimidazole; TFB = tetrafluorobenzobarrelene] have been prepared by reaction of OsH3(Hbiim)(PiPr3)2 with the dimers [M(μ-OMe)(TFB)]2 (M = Rh, Ir). In solution the hydride ligands of these complexes, which form two chemically equivalent unsymmetrical OsH3 units, undergo two thermally activated site exchanges and show two different quantum exchange coupling processes.We thank the DGICYT of Spain (Projects PB95-0806 and PB95-0639-CO2-01, Programa de Promocion General del Conocimiento).Peer reviewe

Synthesis and spectroscopic and theoretical characterization of the elongated dihydrogen complex OsCl2(h2- H2)(NH=CPh2)(PiPr3)2

The referred elongated dihydrogen compounds cannot be described by simply interpolating dihydrogen and dihydrido models. According to the results reported here, it is more appropriate to describe them as complexes containing two hydrogen atoms moving freely in a wide region of the coordination sphere of the metal.We acknowledge financial support from the DGES of Spain (Projects PB95-0806 and PB95-0639-CO2-01). The use of computational facilities of the Centre de Supercomputacio i Comunications de Catalunya (C4) is gratefully appreciated.Peer reviewe

13th EXMATEC ‐ Expert Evaluation and Control of Compound Semiconductor Materials and Technologies.

Producción CientíficaThe photoluminescence imaging (PLi) technique allows for the fast qualification of mc-Si wafers and solar cells, giving information of the presence and distribution of carrier capture centres, which obviously affect the final efficiencies. In this work, we characterize a wide collection of solar cells by PLi, correlating some aspects extracted from the PL images to their efficiencies. The desired goal of this approach is to provide a tool allowing a robust prediction of solar cell efficiency from the PL images of the wafers.40th WOCSDICE ‐ Workshop on Compound Semiconductor Devices and Integrated Circuits held in Europe & 13th EXMATEC ‐ Expert Evaluation and Control of Compound Semiconductor Materials and Technologies, 6-10 June 2016, Aveiro, PortugalMinisterio de Economía, Industria y Competitividad (Project ENE2014- 56069-C4-4-R

Synthesis and characterization of OsX{NH=C(Ph)C6H4}(h2-H2)(PiPr3)2 (X = H, Cl, Br, I): Nature of the H2 unit and its behavior in solution

The hexahydride OsH6(PiPr3)2 (1) reacts with benzophenone imine to give the trihydride derivative (2). The three hydride ligands and the bidentate group of 2 are situated in the equatorial plane of a pentagonal-bipyramidal arrangement of ligands around the metallic center. In solution, two thermally activated exchange processes take place between these hydride ligands, one of them faster than the other one. The reaction of 2 with HCl leads to OsH3Cl(NHCPh2)(PiPr3)2 (3), which evolves in solution into the elongated dihydrogen compound (4). Complex 4 and the related compounds (X = Br (5), I (6)) can be also prepared by protonation of 2 with HBF4·OEt2 in dichloromethane and subsequent treatment with NaX (X = Cl, Br, I). The structure of 4 has been determined by X-ray diffraction. The geometry around the osmium atom can be described as a distorted octahedron, with the triisopropylphosphine ligands occupying two relative trans positions. The remaining perpendicular plane is formed by the mutually cis disposed chloro and dihydrogen ligands and the metalated benzophenone imine group, which has a bite angle of 75.1(1)°. The H2 unit of 4−6 shows a restricted rotational motion in solution. Thus, the 1H NMR spectra in the high-field region are a function of the temperature. Lowering the sample temperature leads to a broadening of the dihydrogen resonances. At 213 K, decoalescence occurs, and at 193 K, two signals are clearly observed. Theoretical calculations suggest that the transition states for the hydrogen exchanges in 2 and 4−6 present dihydrogen-like nature.We acknowledge financial support from the DGES of Spain (Project Nos. PB95-0806 and PB95-0639-CO2-01).Peer reviewe