Rationally Designed Cooperative Self‐Assembled Monolayers Enable Holistic Modulations of Wide‐Bandgap Perovskites for High‐Performance Perovskite‐Silicon Tandem Solar Cells

ABSTRACT Perovskite‐silicon tandem solar cells hold great promise for the development of next‐generation cost‐effective photovoltaic technologies, and their performance gains largely rely on advanced materials and interface engineering of wide‐bandgap perovskite sub‐cells. Herein, we develop a cooperative self‐assembled monolayer (co‐SAM) strategy by incorporating a rationally designed alkyl‐phosphonic acid, 12‐methoxydodecylphosphonic acid (MeODPA), into commonly used carbazole‐based SAMs, leading to an obvious enhancement in the performance of single‐junction wide‐bandgap (WBG) (1.68 eV) and tandem PSCs. We demonstrate that the methoxy terminal group and flexible alkyl chain of MeODPA synergistically improve substrate wettability and molecular coverage of SAMs on the buried substrate, promoting perovskite crystallization and stabilizing the buried interfacial contacts. Moreover, we uncover a previously overlooked function of the co‐SAMs in regulating the PbI 2 distribution at the top surface, which facilitates more effective surface passivation, leading to improved light stability of resultant perovskite films. Leveraging these advancements, we fabricate single‐junction WBG and perovskite‐silicon tandem devices with exceptional power conversion efficiencies (PCEs) of 24.11% and 32.16%, respectively. This work provides a comprehensive understanding of the coordinated effects of co‐SAM on bulk and dual‐interface properties of perovskite films, offering valuable insights for further performance improvements of both single‐junction and tandem perovskite photovoltaics.