J. Löffler

Roll to roll fabrication process of thin film silicon solar cells on steel foil

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process chain are: 1) application of an insulating barrier layer which enables texturization of the rear contact with submicron structures for light trapping; 2) Si deposition with remote, linear PECVD; 3) series interconnection by laser scribing and printing after deposition of the layers (reducing the total number of process steps). The barrier layer is primarily an enabler for monolithic series interconnection of cells, but we show that we can also fabricate any arbitrary sub-micron structure in this layer by hot embossing to achieve optimum light trapping in the solar cells. For deposition of doped and intrinsic silicon layers we use novel remote and linear plasma sources, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. First pin a-Si solar cells have been made on FTO glass, yielding initial efficiencies up to 4.5%. First nip a-Si cells made on steel foil plus textured barrier layer yielded efficiencies of about 3.7%.

20.3% MWT Silicon Heterojunction Solar Cell—A Novel Heterojunction Integrated Concept Embedding Low Ag Consumption and High Module Efficiency

In this paper, we present the successful integration of a silicon heterojunction (HJ) solar cell with metal wrap through (MWT) architecture. This MWT-HJ cell and module technology combines all the advantages of the individual concepts. With this contribution, we demonstrate a record device efficiency of 20.3% achieved using commercial n-type Cz 6-in wafers. To our knowledge, this is the first time cell results for MWT-HJ architecture have been reported. We put this result in perspective, providing a solution for the reduced conductivity of low-temperature silver pastes used for HJ cell fabrication. We propose a method to further increase the solar cell performance up to 4%rel, together with a 50% cost of ownership reduction of the front contact silver, including via and conductive adhesive at the rear. This is possible solely by the optimization of the front metal grid in this MWT structure predicting efficiencies above 21%. MWT-HJ is a fully low-temperature integrated cell and module concept and is also compatible with next-generation thinner wafers.

Metal Wrap through Silicon Heterojunction Solar Cells and First Made Minimodules

In this paper we present the successful integration of a silicon heterojunction (HJ) solar cell with metal wrap through architecture (MWT) and foil basedback contact module technology. With this contribution we show a record cell efficiency of 20.3% achieved using commercial n-type Cz 6 inch wafers and demonstrate an encapsulated cell efficiency of 19.6% achieved on a 2×2 mini-module. To our knowledge this is the first time that module results of MWT-HJ architecture have been reported. In this studies , we propose a method to increase the solar cell performance up to 21% together with a 50% cost of ownership reduction of the front silver metal including via and conductive adhesive. This is possible solely by the optimization of the front metal grid. MWT-HJ is a fully low-temperature integrated cell and module concept compatible also with thinner wafers.

Roll to roll fabrication of thin film silicon solar cells on nano-textured substrates.

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process are: 1) application of an insulating barrier layer which enables monolithic interconnection and texturization of the rear contact with submicron structures for light trapping; 2) Si deposition with remote, linear PECVD; 3) series interconnection by laser scribing and printing after deposition of all layers, which reduces the total number of process steps. The barrier layer is essential for the monolithic series interconnection of cells, but we show that it also enables optimum light trapping in the solar cells. We can fabricate any arbitrary sub-micron surface profile by hot embossing the barrier layer. For deposition of doped and intrinsic silicon layers we use novel remote, linear plasma sou rees, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. The first pin a-Si solar cells have been made on FTO glass, yielding initial efficiencies up to 4.5%. First nip a-Si cells made on steel foil with textured barrier layer yielded efficiencies of about 3.7%.

MW plasma enhanced CVD of intrinsic Si for thin film solar cells

The aim of the thin film silicon PV research program at ECN is the development of highthroughput production technology for high efficiency, microcrystalline and amorphous thin film silicon photovoltaics (PV) on flexible substrates. For this purpose, a roll-to-roll system has been designed and constructed, consisting of three deposition chambers for the continuous deposition of n-type, intrinsic and p-type Si layer. In this paper, we will present optical and electrical characterisation of device quality intrinsic Si layers, deposited with Microwave (MW) plasma enhanced chemical vapour deposition (PECVD), with a special focus on UV-reflection spectroscopy (UVRS). UVRS can be used to determine the crystallinity in very thin silicon layer and is interesting as a possible inline tool for layer quality assessment and crystallinity control.