abstract
Over the past decade, metal halide perovskite semiconductors emerged as the prime candidate materials for next generation high-efficiency multi-junction photovoltaics (PVs). The recent remarkable advancements in monolithic perovskite-based double-junction solar cells (i.e., perovskite/CIGS or perovskite/Si tandem PV) denote just the beginning of a new era in multi-junction PVs. However, to date, the performance of triple-junction PV architectures, such as perovskite--perovskite--silicon architecture, lags considerably behind, with only a limited number of reports on prototypes. In this contribution, we present triple-junction perovskite--perovskite--silicon solar cells, achieving a power conversion efficiency of 24.4%. Achieving such high performances in triple-junction perovskite--perovskite--Si solar cells requires addressing several challenges. These include (1) the sequential processing of high-quality perovskite thin films within the progressively complicated multi-layer architecture, (2) light management to ensure efficient absorption and utilization of sunlight, (3) current matching among the monolithically interconnected sub-cells, as well as (4) the development of low-loss tunnel/recombination junctions for efficient charge transport across the junction. Overcoming these challenges is essential for realizing the full potential of triple-junction perovskite--perovskite--Si solar cells and pushing the boundaries of ultra-high-efficiency PV technologies. A significant challenge in processing triple junctions to date is the most critical junction, the middle perovskite sub-cell. This sub-cell is processed on top of the silicon bottom cell and must withstand the subsequent processing of the wide-bandgap perovskite top cell. In this study, we show that by optimizing the light management for each perovskite sub-cell (with bandgaps of ~1.84 eV and ~1.52 eV for the top and middle cells, respectively), we maximize the current generation to 11.6 mA cm--2. The key to this achievement is the development of a high-performance middle perovskite sub-cell, utilizing a stable pure-\textgreeka-phase formamidinium lead iodide perovskite thin film that is free of wrinkles, cracks, and pinholes. This enables a high open-circuit voltage of 2.84 V in the triple-junction architecture. Notably, non-encapsulated triple-junction devices retain up to 96.6% of their initial efficiency when stored in the dark at 85°C for 1081 hours.