B. González-Díaz

Anisotropic textured silicon obtained by stain-etching at low etching rates

The structure, luminescence and etching kinetics for porous silicon stain-etched at different temperatures are studied. The results reveal that for temperatures below 10 °C and for short etching times, a novel anisotropic structure based on surface roughness preferentially oriented in the 100 direction is observed. At temperatures higher than 10 °C or large etching times, typical macropores and mesopores with non-preferential pore wall orientation are detected. The luminescence spectra of the samples with preferential surface roughness orientation are red-shifted with respect to the samples with typical isotropic orientation. The results are interpreted in terms of average etching rates and pore growth.

Photoluminescence of monocrystalline and stain-etched porous silicon doped with high temperature annealed europium

In this work, for the first time, the photoluminescent emission and excitation spectra of non-textured layers and stain-etched porous silicon layers (PSLs) doped with high temperature annealed europium (Eu) are evaluated. The PSLs are evaluated as a host for rare earth ions and as an antireflection coating. The applied doping process, which consists in a simple impregnation method followed by a high-temperature annealing step, is compatible with the standard processes in the fabrication of solar cells. The results show down-shifting processes with a maximum photoluminescent intensity at 615 nm, related to the transition 5D0 → 7F2. Different initial concentrations of Eu(NO3)3 are evaluated to study the influence of the rare earth concentration on the photoluminescent intensity. The chemical composition and the morphology of Eu-doped PSLs are examined by means of x-ray dispersion spectroscopy, Fourier-transform infrared spectroscopy and scanning electron microscopy. These Eu-doped layers are considered to be applied as energy converters in silicon-based third generation solar cells.

Microscopy analysis of pyramid formation evolution with ultra-low concentrated Na2CO3/NaHCO3 solution on (100) Si for solar cell application.

An analysis of the nucleation mechanism of pyramids formed in (100) silicon in Na2CO3/NaHCO3 solution has been carried out. This texturization process of silicon by means of Na2CO3/NaHCO3 solutions is of special interest because it can be applied to the silicon solar cell industry to texture solar cell surfaces to decrease the front reflection and enhance light trapping in the cells. For this purpose, two microscopy techniques-scanning electron microscopy and atomic force microscopy-have been used to study the different stages of pyramidal nucleation and formation. The different aspects and factors involved in the texturization process require different analysis conditions and microscopy resolution. Tracing the transformation of determined surface areas and structures has been achieved, contributing clarification of the mechanism of pyramid nucleation in Na2CO3/NaHCO3 solutions.

Forensic analysis of Si-based PV module micro-cracking due to standard IEC thermal and mechanical testing procedures

Micro-cracking analysis of Si-based photovoltaic (PV) modules and its effect on the module performance has been under study since a few years but only from a theoretical point of view. Currently there is not a well stablished procedure to evaluate the micro-cracking in order to prevent it and the electrical losses associated when aging and mechanical stress caused produced under normal working conditions and maintenance. In this work we show a forensic analysis of real PV modules uninstalled from a multi-MW PV plant and tested in a certified IEC lab for a micro-cracking analysis using camera based electroluminescent (EL) imaging analysis and solar simulator pre- and post-climate chamber. The results show that the thermal cycles applied to the PV modules produce almost no new micro-cracks but predispose the PV modules to cracking in subsequent mechanical testing. The results are useful for planning the addition of a new film to reinforce the PV module and, consequently, diminish the evolution of these micro-cracks.

PV-battery systems for increasing the share of renewable energy and avoiding repowering lines in islands where grid-parity is reached

PV grid parity has been reached in the Gran Canaria island grid. To diminish the generating cost (

Techno-economic analysis for the placement of a Si-based low-cost solar cells factory in West Africa and compared to China

297.37/MWh on average in Canary Islands in 2013) the new Spanish regulation approved in August 2014 offer substantial incentives for PV investment in insular systems. However, many of the best locations for large PV systems are far away from substations. On the other hand, there are isolated villages at the end of large power lines, where the energy demand is increasing and a combination of PV and storage systems could avoid a costly repowering of the grid. In this work we analyze how capacity combinations of PV systems and Li-ion batteries (405 kWp PV and 1MW/3MWh Li-ion batteries currently located) in a defined area can increase the share of PV energy in the power system and also could transfer capital from costly grid repowering investment to new PV-battery systems.

Optimization of sodium carbonate texturization on large-area crystalline silicon solar cells

The sharp cost reduction in photovoltaic (PV) crystalline silicon cells in recent years has dramatically increased the attractiveness of PV systems in many countries and specific electricity grids. This situation can be objectively described in terms of reached grid parity and the improved access to electricity in places where the power supply is not guaranteed in terms of quality or, simply, it does not exist. One of such places around the world where these conditions are fulfilled is West Africa. In this work a techno-economic analysis is presented for a Si-based low-cost solar cells manufacturing factory in West Africa and it is compared to a similar factory operating in China. A sensitive analysis of the final cost of the solar cells, in terms of USD/Wp is exposed and discussed varying the value of key input parameters into a defined range. The cost of solar cells in the different countries analyzed and other important parameters for business competitiveness serve to define a composite indicator and a ranking of the ten more favorable countries for the location of the PV factory.