Nanoelectronics and photovoltaics research centre imec of Leuven, Belgium (a partner in Solliance and EnergyVille) has improved its 4cm2 perovskite/silicon tandem photovoltaic module, achieving record solar energy conversion efficiency of 23.9% (the first to achieve a module-on-cell stack that outperforms the standalone silicon solar cell).
Perovskite solar cells can achieve high power conversion efficiency, are inexpensive to produce, and have high absorption efficiency in sunlight. The material can be engineered to result in various optical and electronic properties. Additionally, perovskite solar cells or modules can also be used to boost standard silicon 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 silicon solar cells, power conversion efficiencies above 30% can potentially be achieved, surpassing the efficiencies of the best single-junction Si solar cells.
Developed in collaboration with Solliance – a cross-border Dutch-Flemish-German thin-film photovoltaic (TFPV) solar energy R&D consortium in the ELAT (Eindhoven-Leuven-Aachen) region – in 2016 imec presented for the first time a semi-transparent perovskite module, stacked on top of an interdigitated back-contact (IBC) crystalline silicon solar cell in a four-terminal tandem configuration. This achieved an overall power conversion efficiency of 20.2% on an aperture area of 4cm2. Imec’s improvement of this technology has now resulted in record power conversion efficiency of 23.9% for a module-on-cell stack of this size.
“Two innovations are key to this achievement,” explained 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 4cm2semi-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.”
The perovskite/Si four-terminal tandem was realized with matched aperture areas as large as 4cm2for the perovskite module and the silicon solar cell. “Having matched areas of this size makes the fabrication technology more attractive to the solar cell industry,” says Aernouts. “For reference, we have also fabricated a stack of a small perovskite cell (0.13cm2) on top of an IBC c-Si cell (4cm2). In this configuration, the 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%.”