Rational Design and Visualization of Multifunctional Phenothiazine‐Based Self‐Assembled Monolayers for Better Interface Contact in High‐Efficiency and Stable Perovskite Solar Cells

Interfacial modification using self-assembled monolayers (SAMs) is crucial for defect passivation and energy level alignment in perovskite solar cells (PSCs), yet scaling SAMs remains a challenge. Organic SAMs are often too thin for large-area homogeneous layers through spin-coating and their hydrophobic nature complicates solution-based perovskite fabrication, hindering uniform film formation. This study introduces SAM based on phenothiazine core that involves synergistic co-adsorption of a hydrophilic phosphonic acid with phenothiazine core unit for use as a hole transport layer in p-i-n PSCs. The PTZ-PA SAM improves film formation, energy alignment, and hole extraction, achieving a power conversion efficiency above 23.2%. It also maintains stable performance for over 500 h under continuous illumination, indicating its potential for durable PSCs. PTZ-PA increases surface energy, overcoming non-wetting issues and enabling the formation of high-quality perovskite films with improved morphology and crystallinity. The phosphonic acid group coordinates with lead iodide in the perovskite, enhancing electronic charge transfer and mechanical absorption, which facilitates effective p-type charge-selective contacts.