Enhanced Binding of Self-Assembled Monolayers for Efficient and Stable Inverted Perovskite Solar Cell

The inverted p-i-n structure perovskite solar cells (PSCs) have outperformed traditional n-i-p structure PSCs in recent years. A key advancement in these p-i-n PSCs is the replacement of traditional hole transport layers (HTLs) with self-assembled monolayers (SAMs). One of the commonly used SAMs enabling high efficiency is carbazole-based phosphonic acids. However, these carbazole-based SAMs show weak binding with transparent conducting oxides (TCO) and poor interaction with perovskite. This results in suboptimal mechanical robustness of the buried interface in p-i-n PSCs, limiting the long-term reliability of these devices. To address these issues, we propose that strengthening the bonding between SAMs and both transparent conductive oxide substrates and perovskite layers can improve stability. We explored the use of a SAM molecule, which has a high dipole moment and donor-π-acceptor structure, as a replacement for [2-(9H-Carbazol-9-yl)ethyl]phosphonic Acid (2PACz) to enhance the TCO-SAM-perovskite interaction. We find that with this new SAM molecule as the HTL, the interfacial adhesion was enhanced by 2.8-fold due to its stronger binding with TCO and improved interaction with perovskite. As a result, the target PSC achieved a maximum power conversion efficiency of 25.6% (certified at 24.9%) and demonstrated high stability, with a T₈₀ of 900 hours at 85°C.