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Abstract:In a monolithic perovskite/c-Si tandem device, the perovskite top cell has to be deposited onto a flat c-Si bottom cell without anti-reflective front side texture, to avoid fabrication issues. We use optical simulations to analyze the reflection losses that this induces. We then systematically minimize these losses by introducing surface textures in combination with a so-called burial layer to keep the perovskite top cell flat. Optical simulations show that, even with a flat top cell, the monolithic perovskite/c-Si tandem device can reach a matched photocurrent density as high as 19.57 mA/cm Korte, R. Schlatmann, M. K. Nazeeruddin, A. Hagfeldt, M. Gratzel, and B. Rech, "Monolithic perovskite/silicon-heterojunction tandem solar cells processed at low temperature," Energy Environ. Sci. 9(1), 81-88 (2015). 16.

We have applied an optical splitting system in order to achieve very high conversion efficiency for a full spectrum multi-junction solar cell. This system consists of multiple solar cells with different band gap optically coupled via an “optical splitter.” An optical splitter is a multi-layered beam splitter with very high reflection in the shorter-wave-length range and very high transmission in the longer-wave-length range. By splitting the incident solar spectrum and distributing it to each solar cell, the solar energy can be managed more efficiently. We have fabricated optical splitters and used them with a wide-gap amorphous silicon (a-Si) solar cell or a CH3NH3PbI3 perovskite solar cell as top cells, combined with mono-crystalline silicon heterojunction (HJ) solar cells as bottom cells. We have achieved with a 550 nm cutoff splitter an active area conversion efficiency of over 25% using a-Si and HJ solar cells and 28% using perovskite and HJ solar cells.

High-efficiency back-contact heterojunction crystalline Si (c-Si) solar cells with record-breaking conversion efficiencies of 26.7% for cells and 24.5% for modules are reported. The importance of thin-film Si solar cell technology for heterojunction c-Si solar cells with amorphous Si passivation layers in improving conversion efficiency and reducing production cost is demonstrated. Our attempts to reduce the production cost of a heterojunction c-Si solar cell by applying a SiO x layer prepared by a plasma-enhanced CVD method are presented. The characteristics of heterojunction c-Si solar cells are clarified by comparing them with those of practical homojunction solar cells, and crucial targets for industrialization of back-contact heterojunction c-Si solar cells are discussed. Owing to the recent improvement of c-Si solar cells and perovskite solar cells, conversion efficiencies over 30% have become a realistic target by using a two-terminal tandem structure with a heterojunction c-Si solar cell and a perovskite solar cell.