Hole-Transporting Self-Assembled Monolayer Enables Efficient Single-Crystal Perovskite Solar Cells with Enhanced Stability

The difficulty of growing perovskite single crystals in configurations suitable for efficient photovoltaic devices has hampered their exploration as solar cell materials, despite their potential to advance perovskite photovoltaic technology beyond polycrystalline films through markedly lower defect densities and desirable optoelectronic properties. While polycrystalline film absorbers can be deposited on myriad substrates, perovskite single crystals fit for high-efficiency devices have only been demonstrated on hydrophobic hole-transport layers [HTLs, e.g., poly(triaryl amine) (PTAA)], which has severely restricted the avenues for enhancing device efficiency and stability. Herein, we report the growth of mixed-cation FA0.6MA0.4PbI3 perovskite single crystals on a hydrophilic self-assembled monolayer {SAM, [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid), (MeO-2PACz)} HTL surface. Compared with PTAA, the MeO-2PACz SAM promotes the mechanical adhesion of the perovskite on the substrate, enabling the fabrication of inverted solar cells with substantially enhanced operational stability and power conversion efficiencies of up to 23.1%, setting a new benchmark for single-crystal perovskite solar cells.