Perovskite solar cells have many desirable properties, as they can achieve a high power conversion efficiency, are inexpensive to produce, and have a high absorption efficiency in sunlight. The material can be engineered to result in various optical and electronic properties. Perovskite solar cells or modules may also be used to boost standard silicon (Si) solar technology when engineered to absorb a spectral range that is complementary to the optical range of silicon cells. By stacking the perovskite solar cells or modules on top of Si solar cells, power conversion efficiencies above 30% can potentially be achieved, thereby surpassing the efficiencies of the best single junction Si solar cells.
In 2016, imec presented for the first time a semi-transparent perovskite module, developed in collaboration with Solliance, stacked on top of an interdigitated back-contact (IBC) crystalline silicon solar cell in a four-terminal tandem configuration, then achieving an overall power conversion efficiency of 20.2% on an aperture area of 4 cm2. This report lifts that figure to 23.9% for the module-on-cell stack, at the same size. Solliance is a partnership of R&D organizations from the Netherlands, Belgium and Germany working in thin film photovoltaic solar energy (TFPV).
“Two innovations are key to this achievement,” according to Tom Aernouts, group leader for thin-film photovoltaics at imec and perovskite PV program manager at Solliance. “First, a different perovskite material (CsFAPbIBr) was used, largely improving the stability and conversion efficiency of the 4 cm2 semi-transparent perovskite module to 15.3%. Second, the architecture of the stack was optimized for minimal optical losses by adding an anti-reflection texture on top of the module and a refractive index matching liquid between the perovskite module and the Si solar cell.”
“Having matched areas of this (4 cm²) size makes the fabrication technology more attractive to the solar cell industry,” commented Aernouts. “For reference, we have also fabricated a stack of a small perovskite cell (0.13 cm2) on top of an IBC c-Si cell (4 cm2). In this configuration, the power conversion efficiency of the small semi-transparent perovskite cell is 16.7%, outperforming the larger 4cm2 perovskite module due to better perovskite layer properties. Although less attractive from an industrial point of view, the overall power conversion efficiency of this cell-on-cell stack is as high as 25.3%.”