Description
The objective is to investigate sputtering techniques and evaluate their effectiveness compared to state-of-the-art e-beam evaporation techniques in several areas such as the application of the antireflective coating, front and backside metallisation, and passivation layers which become important as the cell concepts get thinner. Targeted improvements: Performance increase for next generation solar cells, reliability improvement (especially during storage), potential cost reduction due to cheaper process Description: The production process of III/V-solar cells includes the deposition of dielectric films for antireflection coatings (ARC) and the coating with metal layers for front- and backside contacts. At present, these layer systems are fabricated at the cell manufacturer using e-beam evaporation techniques. However, for future requirements which can be anticipated by next generation solar cells it is worthwhile to investigate other deposition techniques such as sputtering or PECVD (plasma-enhanced chemical vapour deposition), which are not used in the current production processes. In the field of ARC, future cell concepts make it necessary not only to reduce the reflection in the wavelength range from 250 to 900nm, but up to 1800nm. To obtain such a broadband ARC dielectric materials with special demands on refractive index and transmission need to be deposited. Those materials are e.g. high refractive TiOx, SiC and SiN, which can be deposited by using sputter techniques or PECVD, but not by conventional e-beam evaporation techniques. SiN is also an interesting material regarding edge passivation and investigation in this field aims to enhance the reliability of the product. Furthermore, it was shown that SiC is a possible candidate for backside passivation. Comparing sputter with evaporation methods, the kinetic energy of the layer forming particles in a sputter process is much higher. This could have an effect on metal layer properties such as adhesion of the metal fingers and their conductivity. Furthermore, as for dielectric materials new deposition approaches also offer a variety of alternative metal systems. Further important questions need be addressed in the activity: Are sputter processes and PECVD compatible with lift off processes, how high is the layer stress, and do these processes damage the epitaxial layer structure? Work logic: 1) Definition of the range of suitable materials (for anti-reflection coating and edge passivation as well as front and back side metallization). 2) Definition of the relevant material properties by simulation/modelling. 3) Manufacturing of test samples using sputtering techniques and characterization of the samples 4) Deposition of the relevant layers on cell structures using sputtering techniques 5) Development of further cell processing 6) Characterisation of solar cells with ARC and/or metal contacts applied by sputtering techniques. 7) Definition of a suitable process flows, cost analysis. Procurement Policy: C(1) = Activity restricted to non-prime contractors (incl. SMEs). For additional information please go to EMITS news "Industrial Policy measures for non-primes, SMEs and R&D entities in ESA programmes".
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