Thiophene Substituent Engineering of Carbazole Based Self-Assembled Monolayers for Use in High-Performance Inverted Perovskite Solar Cells

Abstract

Carbazole-based self-assembled monolayers (SAMs) are widely used in inverted perovskite solar cells (PSCs). However, the biased intermolecular assembly of SAM molecules, and the lack of Lewis-basic heteroatoms to efficiently tune the crystallinity of perovskites and passivate the interface defects still limited the further improvement of the efficiency and stability for PSCs involving carbazole-based SAMs. Herein, a novel 3,6-dithiophene carbazole-based SAM molecule (named CzTh) is designed via the substituent engineering strategy, which is demonstrated to effectively solve the obstacles. The theory and experiment find that the introduction of thiophene regulated SAMs with the carbazole core in terms of surface wettability for precursor solvent, energy level alignment, the crystallization of perovskite films and defects passivation, which is attributed to dipole moment changes, and the Lewis base property of S atom. Consequently, the PSCs with CzTh achieved enhanced power conversion efficiency (PCE) and excellent air stability, compared to the commercial SAMs (Me-4PACz). As an “one-stone-three-birds” design strategy for SAMs, the “thiophene-substitution” effectively tunes the perovskite crystallization, passivates the defects, and enhances the hole injection at the perovskite/SAMs interface of inverted PSCs.