Boosting the Dipole Effect of Self-Assembled Monolayers via an Asymmetric Sulfur Functionalization Strategy

Self-assembled monolayers (SAMs) have drawn great attention for their unique molecular properties. However, the symmetrical molecular configuration of the carbazole-based SAMs weakens their dipole effect on the substrate, which impedes further enhancement of the efficiency for inverted perovskite solar cells (PSCs). Thus, fine-tuning the dipole effect of SAM molecules on energy alignment is urgently needed for achieving high-performance molecules. Herein, we propose a molecular strategy of asymmetric sulfur functionalization. By incorporation of the carbazole and S-functionalized benzene groups, a type of asymmetric carbazole-based SAM was designed and synthesized, cited as SCz. The S atom acted as a soft base to form strong Pb–S bonds and optimize the energy level of SCz. The study also found that the cooperative effect of asymmetric structures and S atoms increased the molecular dipole up to 4.2 D, making more matched energy levels of SAM with the perovskite layer. Consequently, the PSCs endowed with SCz achieved a champion efficiency of 21.63%, accompanied by improved device stability. The results indicate that constructing an S-functionalized asymmetric SAM is an effective strategy for accurately regulating energy levels and the dipole effect of the SAM on the substrate.