Magnesium Oxide Buffer Layer for Over 32% Efficiency Four‐Terminal Perovskite/Silicon Tandem Solar Cells

Abstract Perovskite/silicon tandem solar cells have emerged as a promising candidate for next‐generation photovoltaics, offering a pathway to surpass the efficiency limits of single‐junction devices. However, the integration of a buffer layer between the electron transport layer and the transparent electrode is critical for maintaining structural integrity and optimizing charge extraction and stability. Here, the fabrication of a chemically stable and multifunctional buffer layer, magnesium oxide (MgO _x ), via thermal evaporation is demonstrated in four‐terminal perovskite/silicon tandem solar cells. The introduction of MgO _x enhances electron extraction while effectively mitigating damage caused by the sputtering process used for subsequent layers. As a result, the optimized device achieves a power conversion efficiency exceeding 32%, along with exceptional operational stability, MgO _x device retains 80% of its initial efficiency after 400 h of continuous MPPT testing. This work highlights the pivotal role of buffer layer engineering in advancing high‐performance tandem solar cells and provides a scalable route toward efficient and durable perovskite/silicon photovoltaics.