Chiral Aza‐Helicene Phosphonic Acids for Stabilizing Efficient Perovskite‐Silicon Tandem Solar Cells

Abstract The popular planar carbazole‐based hole‐selective self‐assembled molecules (SAMs) for perovskite solar cells (PSCs) suffered from intrinsic instability toward electric potential, heat, and light illumination. To address this issue, herein, we report a kind of chiral helically shaped SAM, aza‐helicene phosphonic acid A5HPA, and A7HPA, featuring their self‐assembly attributed to the extended nonplanar π‐conjugated system of aza‐helicene with highly intrinsic stability toward thermal aging, light soaking, and electrical oxidation. Due to the increased torsion degree of the helicene backbone and the improved helical chiral molecular self‐consistency, P and M enantiomers of A7HPA molecules tend to stack in an alternating pattern similar to “gear mesh,” leading to reinforced intermolecular π–π interactions and conjugation effect to rigidify the hole transport layer. Consequently, the A7HPA‐based single‐junction wide bandgap PSC and perovskite‐silicon tandem solar cell exhibited impressive long‐term stability under both damp‐heat and light‐thermal synergetic stress tests and provided 23.41% and 33.06% (certified as 32.57%) power conversion efficiencies, respectively.