Carbazole‐Based Self‐Assembled Monolayers for Hole Transport in Photovoltaics: A Molecular Engineering Perspective

ABSTRACT Self‐assembled monolayers (SAMs) have proven to be highly efficient hole‐transporting layers (HTLs) due to their advantages, including low cost, minimal material consumption, ease of synthesis, negligible optical loss, and exceptional stability. Recently, carbazole‐based SAM HTLs have considerably improved the power conversion efficiency (PCE) of organic solar cells (OSCs) and perovskite solar cells (PSCs)—with PCEs reaching 21% and 27%, respectively. This review begins with a concise overview of the chemical structure of SAMs, emphasizing the recent advancements achieved by carbazole‐based SAMs in the photovoltaics (PVs) sector. We then systematically summarize the modifications made to the chemical structure of carbazole‐based SAMs to optimize their interface dipole, surface wettability, and interface defects. Especially for functional group, the modification techniques are categorized into four main types: methoxylation, conjugation, halogenation, and asymmetrization. Finally, several challenges, including solubility, film quality, and stability, along with potential solutions for these issues are discussed. We hope this review serves as a valuable guide and source of inspiration for the design of SAM HTLs, ultimately enhancing the performance of PV devices.