Progress and challenges in perovskite photovoltaics from single- to multi-junction cells

Organic-inorganic hybrid perovskite solar cells have attracted unprecedented attention in recent years due to their high power conversion efficiency, ease of fabrication and potential to yield low cost photovoltaic modules. The power conversion efficiency of the record lab-scale cell is 23.3%, which is higher than record lab-scale cells for commercially dominant multi-crystalline silicon and CdTe solar cells. Owing to their high open-circuit voltage, sharp absorption edge, tunable bandgap and solution processibility, perovskite solar cells are ideal candidates for incorporation in tandem solar cells, which in practice can exceed even the theoretical limits for a single junction cell. In this review, following the theoretical efficiency limits of single and tandem solar cells, we review the development of single-junction perovskite solar cells with a focus on the material structure, bandgap engineering and crystallization strategies. We then focus on the key challenges in perovskite-based tandem solar cells, showing the recent advances in high-efficiency organic-perovskite, inorganic-perovskite, and perovskite-perovskite tandem cells. Finally, we map out research directions to further develop perovskite-based tandem solar cells.