Dip-coated SAM/CPA composite hole transport layers for high-efficiency vapor-deposited perovskite solar cells

Recent advancements in inverted perovskite solar cells have highlighted the role of self-assembled monolayer (SAM) hole transport layers, which offer thin profiles, ease of fabrication, and effective hole extraction, thereby enhancing solar cell efficiency. However, producing high-performance SAM films on rough substrates using traditional spin-coating is challenging due to the large, flat nature of typical SAM molecules, which leads to aggregation and insufficient film density. This can expose substrate areas to the perovskite layer, risking short circuits and compromising efficiency and stability. To overcome these challenges, we adopted a dip-coating adsorption method to prepare the SAM film while introducing chloromethylphosphonic acid (CPA) small molecules to occupy aggregation-induced vacancies. Our findings show that SAM molecules can successfully form dense films on rough FTO substrates using dip-coating, with CPA effectively filling gaps. Moreover, the chlorine groups in CPA enhance the vapor phase growth of the perovskite layer, reducing voids and promoting larger grain sizes. This dip-coating technique facilitated the development of a high-performance SAM/CPA composite hole transport layer, resulting in a perovskite solar cell with a power conversion efficiency of 21.37 %, which maintained 82.44 % efficiency after 1000 h of operation at maximum power.