Hybrid Self-Assembled Molecular Interlayers for Efficient and Stable Inverted Perovskite Solar Cells

Abstract

Self-assembled molecules (SAMs) have been widely employed as hole transport layers (HTLs) in inverted perovskite solar cells (PSCs). However, the carbazole core of [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) is insufficiently effective for passivating defects at the “bottom” of perovskite films, and the weak anchoring ability of phosphate groups toward the NiO_x substrate appears to promote the formation of dimers, trimers, and higher-order oligomers, resulting in molecular accumulation. Herein, a novel technique is proposed to combine Me-4PACz with different thiol molecules to modify the buried interface of PSCs. Molecular dynamics simulations and infrared scattering-type scanning near-field optical microscopy (IR s-SNOM) results show that co-depositing Me-4PACz with thiol molecules forms hybrid SAMs that densely and uniformly cover the NiO_x surface. The island-like structure of the hybrid SAMs serves as a template for forming the perovskite bulk heterojunction composed of interpenetrating networks of MA-rich and FA-rich domains, enabling efficient charge generation and suppressed bimolecular recombination. Particularly, (3-mercaptopropyl) trimethoxysilane (MPTMS) effectively prevents Me-4PACz aggregation by forming a multi-dentate anchor on the NiO_x surface through hydrolytic condensation of ─OCH₃ groups, while its ─SH groups passivate uncoordinated Pb²⁺ at the perovskite/HTL interface. Consequently, the resulting hybrid SAMs-modified PSC achieve a champion photoelectric conversion efficiency (PCE) of 25.4% and demonstrated better operational stability.