accounts for only ≈3% of global electricity generation. [1] However, PV is experiencing an accelerated growth globally with >130 GW installed in 2020, an acceleration that should continue in the future to provide 20-30% of the global electricity on the 2050 horizon. [2] The key to materializing this ambitious goal is to reduce the cost of PV-generated electricity to make solar energy significantly cheaper than that produced by fossil fuels, and to promote the implementation of storage technologies. [3] Currently, the major cost component of a PV system stems from the balance-ofsystems (BOS). [4] The BOS refers to all the components of a PV system other than the solar module, including wiring, inverters, land, installation, labor, etc. With cell costs typically accounting for less than 20% of the total module cost (and module costs typically account for around 40% at the system level), [4,5] increasing power conversion efficiency at the cell and module level is the most efficient way to reduce the levelized cost of electricity (LCOE), provided this efficiency gain comes at affordable manufacturing costs. [6] Increasing the solar module efficiency is even more important for residential rooftops, facades, or other applications where
This review focuses on monolithic 2-terminal perovskite-silicon tandem solar cells and discusses key scientific and technological challenges to address in view of an industrial implementation of this technology. The authors start by examining the different crystalline silicon (c-Si) technologies suitable for pairing with perovskites, followed by reviewing recent developments in the field of monolithic 2-terminal perovskite-silicon tandems. Factors limiting the power conversion efficiency of these tandem devices are then evaluated, before discussing pathways to achieve an efficiency of >32%, a value that small-scale devices will likely need to achieve to make tandems competitive. Aspects related to the upscaling of these device active areas to industryrelevant ones are reviewed, followed by a short discussion on module integration aspects. The review then focuses on stability issues, likely the most challenging task that will eventually determine the economic viability of this technology. The final part of this review discusses alternative monolithic perovskite-silicon tandem designs. Finally, key areas of research that should be addressed to bring this technology from the lab to the fab are highlighted.