New progress in the fabrication of n–i–p micromorph solar cells for opaque substrates

In this paper, we investigate tandem amorphous/microcrystalline silicon solar cells with asymmetric intermediate reflectors grown in the n–i–p substrate configuration. We compare different types of substrates with respect to their light-trapping properties as well as their influence on the growth of single-junction microcrystalline cells. Our most promising back reflector combines a textured zinc oxide film grown by low-pressure chemical vapor deposition, a silver film for reflection, and a zinc oxide buffer layer. Grown on this substrate, microcrystalline cells exhibit excellent response in the infrared while keeping high open-circuit voltage and fill factor, leading to efficiencies of up to 10.0%. After optimizing the morphology of the asymmetric intermediate reflector, we achieve an n–i–p micromorph solar cell stabilized efficiency of 11.6%, using 270 nm and 1.7 μm of silicon for the absorber layer of the amorphous top cell and the microcrystalline bottom cell, respectively. Using this original device architecture, we reach efficiencies close to those of state-of-the-art n–i–p and p–i–n micromorph devices, demonstrating a promising route to deposit high-efficiency thin-film silicon solar cells on opaque substrates.

► High-efficiency μc-Si:H cells were grown on ZnO textures combined with hot Ag.
► The roughness of ZnO intermediate reflectors is well controlled by plasma etching.
► ZnO asymmetric intermediate reflectors lead to optimum micromorph Voc.
► State-of-the-art micromoprh cell efficiency is reached via this cell architecture.