Texturing of multicrystalline silicon by laser ablation

The application of laser ablation for texturing purposes represents a suitable alternative to common wet chemical texturing schemes. In this paper, a patented texturing scheme, consisting of a laser ablation step followed by plasma-chemical removal of the laser debris has been applied to conventional screen-printed multicrystalline silicon (mc-Si) solar cells. Depending on the laser parameters weighted reflectance values below 20 % are achievable with aspect ratios above 1 (depth to width). The application of the Laser-Plasma texturing scheme to conventional mc-Si solar cells results in an increase of jsc of about 1 mA/cm2 compared to planar etched reference cells indicating the improved optical properties. With a further adaptation of the front side screen-printed metallisation grid, significant improvements of the cell efficiency could be achieved in the future

Characterization of laser-fired contacts in PERC solar cells: SIMS and TEM analysis applying advanced preparation techniques

In this study we apply ion-beam supported preparation techniques for both mesa formation by trench sputtering and FIB 'lift-out' lamella cutting for dynamic SIMS and TEM analysis of laser-fired Al point contacts on Si, respectively. Detailed compositional and structural informations about the metallurgical contact formation process are obtained combining both characterization techniques. While TEM micrographs and microdiffraction patterns reveal a mixture of Al- and Si-crystals within the similar to 1 mu m thick Al rich re-solidified surface layer according to the AI-Si phase diagram, spatially resolved SIMS depth profiling indicates ppm-range Al-diffusion a few hundred nm into the buried, substantially undisturbed Si-lattice. (c) 2006 Elsevier B.V. All rights reserved

High Mobility Transparent Conductive Oxides for Silicon Heterojunction Solar Cells Deposited by Rotatable Magnetrons

Sputtered indium tin oxide ITO is a widespread used material for application as transparent conducting oxide as the front contact of rear junction silicon heterojunction solar cells. Standard ITO films suffer from too high parasitic absorption in both the short and the long wavelength range. The aim of this contribution is to investigate lower absorbing TCOs deposited with industrial DC sputtering from rotatable targets. High Voc values gt;735 mV demonstrate that in spite of the high power industrial DC sputter process no significant sputter damage is observed, independent of the target material. Cell efficiencies up to 23.3 are obtained with titanium doped ITiO and tin doped indium oxide ITO 99 1 . The highest short circuit current values of 39.6 mA cm2 are reached with an ultimately low carrier and high mobility indium oxide based material. The cell efficiency in this case, however, is over compensated by a too low FF, mostly due to a higher contact resistivity and TCO sheet resistances. We ascribe this effect to the very low carrier concentratio

Innovative and efficient production processes for silicon solar cells and modules - SOLPRO IV

The joint project of wafer, solar cell and solar module manufacturers and research institutes called "SOLPRO" has been continued. Within SOLPRO IV the "board of experts: innovative and efficient production processes for silicon photovoltaic modules" was composed of 13 German enterprises and scientifically supported and co-ordinated by the Fraunhofer ISE and the Fraunhofer IPT. The consortium of participating enterprises covers almost completely the production chain from the as-cut-wafer to the completed module both on the production side as well as on the equipment manufacturing side. The multidisciplinarity of the SOLPRO consortium creates a fruitful ground for the identification and assessment of optimisation and innovation potentials within the production technology based on cells and modules from silicon wafers. Within the different sub-projects various results have been obtained, which are summarised in this paper. For example thorough experiments on alternatives to the standard edge isolation process in a plasma barrel etcher have shown, that the use of a fast laser ablation process instead of standard plasma barrel etching can lead to a significantly improved material flow in a production scale environment while maintaining or even improving the cell efficiency

Analysis of laser-fired local back surface fields using n+np+ cell structures

In order to investigate our new LFC process for the formation of local contacts on a dielectrically passivated rear surface, we have analyzed n/sup +/np/sup +/ structures processed identically to the standard n/sup +/pp/sup +/ cells except for the doping type of the base material. For these devices the p/sup +/-emitter is formed point-like at the rear surface by Al-alloying during the LFC process. The observation of voltages above 600 mV is a clear proof of the creation of a local Al diffusion. Since a pn-junction is much more decisive for a solar cell than a BSF, the n/sup +/np/sup +/ structures were used to understand the physics of the LFC contact and to optimize the laser parameters resulting in efficiencies of 20% for n/sup +/pp/sup +/ LFC cells in a resistivity range between 0.5 Omega cm and 10 Omega cm