Catechol‐Functionalized Self‐Assembled Monolayer for Highly Efficient Sn─Pb and All‐Perovskite Tandem Solar Cells

Abstract

ABSTRACT The performance of all‐perovskite tandem solar cells is strongly dependent on the properties of Sn‐Pb narrow‐bandgap subcells. Self‐assembled monolayers (SAMs) such as 2PACz have shown great success in lead‐based perovskite solar cells (PSCs), yet their application in Sn─Pb PSCs remains limited, largely due to suboptimal carrier‐extraction capability and insufficient interfacial stability. Here, we design and introduce a new SAM, 9‐(3,4‐dihydroxyphenyl)‐9H‐carbazole (DOPhCz), featuring a conjugated catechol anchoring group, into Sn─Pb PSCs for the first time. The well‐formed and uniform DOPhCz SAM layer promotes more homogeneous perovskite nucleation and improved crystallinity, lowering interfacial defect density and enhancing device performance compared with phosphonic‐acid‐based [2‐(9Hcarbazol‐9‐yl)ethyl]phosphonic acid (2PACz)M. In addition, DOPhCz accelerates hole extraction and reduces chemical perturbation during device operation. As a result, the DOPhCz‐based Sn─Pb PSC achieves a power conversion efficiency of 24.17%, outperforming its 2PACz‐based counterpart (22.87%) and exhibiting significantly improved operational stability. When applied in all‐perovskite tandem solar cells, a high efficiency of 28.30% is obtained. This work establishes a coherent mechanism for SAM‐induced interfacial stabilization and provides valuable insights for molecular engineering of high‐performance all‐perovskite tandem devices.