Reinforcement of Carbazole-Based Self-Assembled Monolayers in Inverted Perovskite Solar Cells

Abstract

Self-assembled monolayers (SAMs) with excellent hole conduction capabilities significantly improve the performance of inverted perovskite solar cells (PSCs). However, the amphiphilic nature of SAMs causes the spontaneous formation of spherical micelles in solution, limiting their surface coverage and uniformity on indium tin oxide (ITO) substrates. Furthermore, the distribution of the SAMs directly affects the morphology of perovskite films and the charges transfer properties at the buried interface. This study employs a cosolvent strategy combining n-butanol and dimethyl sulfoxide to improve the uniform spreading of SAMs on ITO. The synergistic interaction between the solvent molecules smooths the surface of [2-(3,6-dimethoxy-9H-carbazol-9-yl) ethyl] phosphonic acid (MeO-2PACz) and enhances its surface coverage. The cosolvent based MeO-2PACz has the characteristics of concentrated surface potential distribution and high work function, exhibiting uniform and enhanced P-type behavior. Additionally, the cosolvent-treated SAMs provide uniform nucleation sites for the crystallization of perovskite, effectively eliminating void defects at the buried interface and improving the crystallinity of perovskite films. Consequently, the optimized device achieves a power conversion efficiency (PCE) of 25.51% and a fill factor of 84.38%. Furthermore, the ordered SAMs improve the stability of PSCs, with encapsulated device retaining 92.63% of its initial PCE after operating for 1500 h under simulated AM 1.5G standard irradiation in air at 65 °C.