With single junction crystalline silicon (c-Si) approaching its practical efficiency limit of 26%, perovskite solar cells have rapidly emerged as a potential game-changing technology in an always more competitive photovoltaics market. Indeed, perovskite cells not only promise low-cost production but they also demonstrate high efficiency potential. Of particular interest is the fact that they also possess a wide band-gap with low sub-gap absorption that make them the candidate of choice to form high-efficiency tandem devices in combination with a narrow-gap absorber, such as silicon. First simulations have shown a potential efficiency beyond 30% for perovskite/c-Si tandem cells.

Here, we present and compare the two most common tandem architectures: the four-terminal tandem configuration, which features two independently processed sub-cells mechanically stacked atop each other, and the monolithic configuration, where the top cell is directly deposited on the bottom cell. The former offers a wide freedom of choice of processes for both sub-cells, whereas the latter has the significant advantage of needing fewer transport and electrode layers, which benefits the optical performance, and is likely the most attractive industrial tandem architecture.

In particular, we show a total efficiency in excess of 25% with four-terminal measurements thanks to our high-efficiency semi-transparent perovskite top-cells with steady state measurement >15% (MPP tracked). In parallel, we demonstrate perovskite layers processed at low temperatures (<200°C) that are compatible with the requirements for integration with high-efficiency silicon heterojunction bottom cells. The excellent layer uniformity achieved by optimizing the perovskite layer deposition allows for a monolithic tandem device with a record efficiency of more than 20% with an aperture size of >1cm². This paves the way for device upscaling. We also show the influence of the bottom cell on the device optics and performance by comparing flat, one-side textured and double-side textured silicon heterojunction cells. Furthermore, we demonstrate how each layer thickness has to be optimized to maximize but also match the currents of the two sub-cells. This effort resulted in a monolithic tandem cell with a short-circuit current density of 17 mA/cm² and an open-circuit voltage above 1.7 V, yielding an efficiency over 20%. Finally, we show how a proper light management can boost the performance for both monolithic and four-terminal configurations.

In summary, we demonstrate highly efficient perovskite/crystalline silicon monolithic tandem cells and four-terminal tandem measurements with efficiencies well beyond 20% on size larger than 1cm² and show several light management strategies that are crucial to further improve device performance.