Self-Assembled Monolayer-Mediated Crystallization Improvement and Energy Level Optimization in Inverted Perovskite Solar Cells

Abstract

The improved crystallization and precise energy level alignment achieved through self-assembled monolayers (SAMs) implementation constitute a critical technological advancement, facilitating inverted perovskite solar cells (PSCs) with simultaneously enhanced power conversion efficiency (PCE) and operational stability. Here, a benzocarbazole-derived SAM, BCPPA, is designed and synthesized as a hole-transporting layer (HTL) by fusing an additional benzene ring in one side of the carbazole core. In comparison to the commonly used carbazole-derived SAM of MeO-2PACz, BCPPA exhibits a larger molecular dipole moment, a deeper HOMO energy level, and a more hydrophobic character. These factors contribute to a favorable buried interface between the SAM and the perovskite, thereby leading to an optimal crystallization of perovskite films and an improved energy level alignment. Additionally, the BCPPA-based interface significantly reduces trap state density and suppresses nonradiative recombination. As a result, the BCPPA-based PSC achieves a champion PCE of 25.28% (certified at 25.01%), surpassing the MeO-2PACz-based device with a PCE of 24.44%. The unencapsulated BCPPA-based devices maintain 72% and 84% of their initial PCEs after aging at 85 °C for 600 h and tracking at maximum power point (MPP) for 512 h, respectively. The asymmetric SAM molecule is promising for fabricating highly efficient and stable inverted PSCs.