Prospects and challenges for perovskite-organic tandem solar cells

Over the past decade, the power conversion efficiencies (PCEs) of single-junction perovskite solar cells (PSCs) have improved dramatically to reach 25.7%, gradually approaching their efficiency limit. To surpass the theoretically predicted values for single-junction solar cells, constructing multi-junction (tandem) solar cells (TSCs) is a promising route to more efficiently utilize solar energy with lower thermalization loss to potentially achieve a PCE >40%. Among various kinds of tandem cells, the perovskite-organic TSCs (PO-TSCs) are fascinating because they take advantage of the complementary properties between organic solar cells (OSCs) and PSCs. They hold great promise to surpass existing TSCs regarding device performance, manufacturing cost, and potential applications. Very recently, the advent of Y6-series non-fullerene acceptors (NFAs) has ignited the vigorous progress of OSCs to enable an unprecedented advancement for PO-TSCs. In this perspective, the need of transitioning from single-junction to tandem solar cells is elucidated first, followed by providing a thorough comparison among the mainstream perovskite-based multi-junction solar cells. Then, the most pressing topics in perovskite/organic sub-cells and PO-TSCs are discussed, including phase segregation, structure-property-performance relationship, energy loss, interconnecting layers (ICLs), and long-term stability. In the end, perspectives on the core aspects related to the future development of PO-TSCs are provided.