Influence of sequential perovskite deposition at the self-assembled monolayer interfaces in inverted perovskite solar cells

Abstract

Perovskite solar cells (PSCs) have gained significant attention in the energy sector due to their rapid advancements. Inverted PSCs, known for their compatibility with low-temperature processing and tandem cell integration, have been a focal point of research, particularly with self-assembled monolayers (SAM) employed as the hole transport layer (HTL). However, the sequential spin-coating method, involving PbI₂ deposition followed by an organic halide layer to form the perovskite film, poses challenges for SAM-based HTLs, as repeated exposure to polar solvents can disrupt the SAM, and detached molecules may agglomerate randomly during perovskite crystallization, further hindering charge transport and increasing leakage current. In this study, we fabricated SAM-based devices using both one-step and two-step spin coating processes followed by morphological, structural and interfacial characterizations. Our results reveal that SAM-based devices suffer pronounced performance losses in two-step process due to interfacial degradation and morphological change. Introducing SAM molecules into the PbI₂ precursor serves as a mechanistic validation, demonstrating that replenishing desorbed SAM can partially restore the buried interface. These findings highlight solvent-induced SAM desorption as a critical yet previously overlooked factor in sequential processed inverted PSCs.