N-Type Self-Assembled Monolayers (SAMs): The Next Star Materials in the Perovskite Photovoltaic Field

Self-assembled monolayers (SAMs) play a critical role in modifying the buried interface of perovskite solar cells (PVSCs) by modulating the crystallization dynamics of perovskites and adjusting energy level alignment between perovskite layer and electrode. The integration of p-type SAMs has driven the power conversion efficiency (PCE) of inverted p-i-n structured PVSCs to a world record efficiency of 26.7%. However, in PVSCs with traditional n-i-p structures, n-type SAMs have not yet achieved comparable breakthroughs. Therefore, to unlock the full potential of n-type SAMs, this review provides a comprehensive summary of their molecular structures, deposition methods, and passivation mechanisms. Recent advances in various n-type SAMs, including fullerene-based, naphthalene imide-based, benzene-based SAMs, and SAMs with other structures have been discussed in detail. Finally, future research directions and their associated challenges are outlined to guide efforts toward realizing the full potential of n-type SAMs in PVSCs.