Metal halide perovskite solar cells have achieved impressive power conversion efficiencies, reaching ~26% for single-junction and over 34% for perovskite-silicon tandem devices. However, challenges related to efficiency losses and long-term stability still hinder their widespread adoption. A significant factor contributing to these losses is the suboptimal performance of conventional charge transport layers. Recently, self-assembled monolayers (SAMs), particularly carbazole-based ones like 2PACz, have shown promise as superior hole transport layers (HTLs), offering improved energy alignment, reduced parasitic absorption, and enhanced device stability. Specifically, their tunable dipole moments and ability to modify the work function of transparent electrodes enable precise control of interface energetics and surface properties. Recently, it has also been understood that forming SAMs from blends of 2PACz derivatives with different functionalization has enabled precise tuning of the valence band energy level alignment at the HTL interface, which led to improved photostability of wide bandgap PSCs [1]. Therefore, functionalization of SAMs not only optimizes electronic alignment but also influences perovskite film morphology by altering substrate surface energy, which in turn affects the perovskite film’s photophysical properties and the solar cell device performance.

In this study, we precisely blended SAM molecules containing polar and non-polar functional groups to simultaneously modulate the surface energy and electronic energy levels of the resulting SAM/ITO substrates. This approach produced substrates with water contact angles ranging from 56° to 74° and photoemission onsets between 5.0 eV and 5.4 eV. Utilising these substrates, we systematically examined how variations in surface energy influence perovskite film coverage, morphology, and photophysical behaviour. As the hydrophobicity of the SAM blends increased, we observed reduced film coverage and smaller grain sizes, which correlated with decreased photoluminescence quantum yield, photoconductivity, and carrier mobility, as determined by time-resolved THz spectroscopy. Transient reflectance (TR) and gated-CCD-based time-resolved photoluminescence (TRPL) measurements further revealed how SAM hydrophobicity affects excited-state dynamics and recombination from shallow trap states. Finally, we explore how the simultaneous tuning of surface energy and interfacial energetics in SAM blends influences overall device performance.