Highly efficient and stable perovskite solar cells via a multifunctional hole transporting material

The hole-transporting material (HTM) plays a crucial role in the performance and stability of perovskite solar cells (PSCs). Ideally, it facilitates lossless charge transfer and suppresses charge recombination and ion migration between the perovskite and electrode. These bulk and interface functionalities require tailored electronic, structural, and chemical properties of the material and film. Here, we report a multifunctional organic HTM T2 based on a thiomethyl-substituted fluorene arm and spiro-[fluorene-9,9′-xanthene] core exhibiting enhanced hole extraction and reduced interface recombination compared with the benchmark HTM spiro-OMeTAD. T2 exhibits strong interactions with adjacent layers, which effectively inhibit interlayer ion migration, leading to enhanced stability. In combination with thermally evaporated perovskite films, power conversion efficiencies of 26.41% (26.21% certified) and 24.88% (certified) have been achieved for 0.1 and 1.0 cm2 PSCs. The excellent performance together with a scalable and low-cost synthesis laid a solid foundation for the future large-scale application of PSCs.