FRAUNHOFER INSTITUTE FOR SOLAR ENERGY SYSTEMS ISE

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1 Epitaxy Wrap Through – our CRYSTALLINE SILICON concept for back contact epitaxial wafer equivalents. THIN-FILM SOLAR CELLS 2 Epitaxial Lateral Overgrowth – advanced light trapping schemes for thin-film solar cells. Crystalline silicon thin-film (c-SiTF) solar Development of High Speed Epitaxial cells present a promising concept to Silicon Deposition Tools combine the advantages of conventional The development of a reliable epitaxial wafer-based silicon solar cells with those deposition and recrystallization process for of thin-film solar cells: high and stable ef- crystalline silicon layers, which are trans- ficiencies and low production costs. In our ferable into the photovoltaic industry, is approach, the electrically active base of the one of our top priorities and competences. solar cell with a thickness of a few tens of For a long time, we have been focussing micrometers is grown upon a substrate ma- on atmospherical pressure chemical vapor terial, which gives the necessary mechanical deposition (AP-CVD) at temperatures up stability. Subsequently, well-established to 1300°C using chlorosilane as the silicon cell process technology from wafer-based carrier gas. This process is well-known from Fraunhofer Institute for solar cells can be applied. Research and microelectronics, but had to be radically ad- Solar Energy Systems ISE development at Fraunhofer ISE cover the apted for photovoltaic applications in terms Heidenhofstr. 2 entire manufacturing chain: of throughput of the equipment at the 79110 Freiburg, Germany n development of substrates from expense of higher tolerable defect densities Phone +49 761 4588-0 low-cost silicon and ceramics of the layers. At Fraunhofer ISE, we have www.ise.fraunhofer.de n adapted functional coatings developed different deposition reactors, (e.g. of silicon carbide) ranging from very flexible batch-type Silicon Photovoltaics – Feedstock, n recrystallization of silicon laboratory setups to large multi-chamber Crystallization and Wafering n deposition of silicon layers with deposition systems with the option of con- Dr Stefan Janz customized doping profiles tinuously depositing p- and n-type doped Phone +49 761 4588-5636 n solar cell processes as well as new epitaxial layers. Our latest development, [email protected] module concepts specifically adapted the ProConCVD, has been designed for to our thin-film technology near-industrial throughput demonstrating

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low-cost high-quality silicon epitaxy for we are working on integrated designs 1 Large chemical vapor deposition PV. When using non-silicon substrates, a with customized single cells which are reactor for inline applications. thin polycrystalline seed layer is deposited interconnected with printing technologies. 2 Zone Melting Recrystallization device. which is subsequently recrystallized. For this purpose a batch-type and a continuous Innovative Solar Cell Processes zone melting recrystallization equipment The advantage of c-SiTF solar cells is their have been developed and are available. compatibility with wafer solar cell process technology. Beyond these, we are develo- Solar Cell and Module Concepts ping specially adapted cell process steps for Our so-called wafer-equivalents, thin c-SiTF solar cells, which also can be of great crystalline silicon layers on conductive interest for wafer processing: carrier substrates, can be processed to solar n epitaxially grown emitters and back cells just like “normal” silicon wafers. They surface fields which offer a large variety profit from nearly any progress achieved of dopant profile designs not limited by in the area of standard wafer solar cells, diffusion and with very short process like e.g. passivation or metallization times technology. Some recrystallized wafer n light trapping mechanisms such as equivalents (RexWE) and module concepts structuring the back surface by epitaxial however, based on cost-efficient substrates lateral overgrowth, or plasma texturing, (such as e.g. zirconium silicate ceramics), creating very effective textures with require innovative methods for contacting extremely low surface removal and interconnection of the single cell. One n chemical vapor etching, i.e. the approach is a wrap-through cell concept chemical etching of silicon with HCl gas where holes are drilled into the substrate at elevated temperatures, able to with a laser which enables rear contacting substitute wet chemical damage etching Cell efficiencies of crystalline silicon of either the base or the emitter from the or time-consuming external impurity thin-film solar cells on monocrystalline non-illuminated side. On the module level, gettering Cz substrates.