Throughput optimized a-Si/μc-Si tandem solar cells on sputter-etched ZnO substrates

Recently, Applied Materials has demonstrated the ability to manufacture large area a-Si/μc-Si thin film modules with total area efficiencies of 10% and above. Reducing the production costs is now the key objective for an economic success of this technology. Decreasing the absorber layer thickness or increasing the deposition rate can reduce the cost significantly because the PECVD deposition of the silicon layers is one of the main cost contributors. But this would also reduce the conversion efficiency of amorphous/microcrystalline tandem cells (a-Si/μc-Si TJ cells). Therefore, optimizing TJ cells for maximal productivity requires a careful balancing of layer thicknesses and deposition rates. In this paper we studied the impact of deposition rates and absorber layer thicknesses for top and bottom cells. The reduction of the bottom cell (BC) thickness from 2 μm to less than 1 μm showed only a small impact on the stabilized module efficiency while having a big impact on the productivity of a production line. The influence of the top cell (TC) deposition rate on the other hand results in a big decrease of the efficiency while having only a small impact on the line output. 10.2% stable mini-module efficiency could be achieved with 900 nm BC thickness, reducing the deposition time by 50%.