Solvent and Deposition Method-Driven Optimization of Carbazole Phosphonic Acid Monolayers for Controlled Perovskite Growth on ITO Substrates

This study investigates the optimization of (2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl)phosphonic acid (MeO-2PACz) ultrathin self-assembled monolayers (SAMs) on indium tin oxide (ITO) substrates, which serve as templates for the controlled growth of methylammonium lead iodide perovskite films. The influence of solvent composition and deposition method on the structural properties of the SAM and its effect on the perovskite morphology are investigated by using polarization modulation infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy. Our results show that the addition of 2% toluene to an ethanol solution during spin coating results in a denser, more organized SAM, with molecules exhibiting a 40° tilt angle relative to the surface normal. This indicates improved molecular packing compared with SAMs deposited in pure ethanol. Our analysis indicates that the SAM chemically binds to ITO primarily through PO32– groups in the presence of toluene, whereas −PO2OH– contributes when ethanol is used alone. The optimized SAM was shown to significantly enhance perovskite crystal growth, producing larger, more homogeneously distributed crystals (∼400 nm) compared to smaller, less ordered crystals grown on less optimized layers. These results highlight the critical role of SAM structure and deposition conditions in controlling perovskite film quality and provide insights for improving the performance of hybrid perovskite devices.