Mitigating the amorphization of perovskite solar cells by using atomic layer deposition alumina

Abstract

Atomic layer deposition of aluminum oxide (ALD-Al₂O₃) layers has been extensively studied for stabilizing perovskite solar cells (PSCs) against environmental stressors, such as humidity and oxygen. In addition, the ALD-Al₂O₃ layer acts as a protective barrier, mitigating the pernicious halide ion migration from the perovskite toward the hole transport interface. However, its effectiveness in preventing the infiltration of ions and additives from the hole-transport layer into perovskites remains insufficiently understood. Herein, we demonstrate the deposition of a compact ultrathin (~0.75 nm) ALD-Al₂O₃ layer that conformally follows the morphology of a triple-cation perovskite film over a large area. This promotes effective mechanical adhesion of the spiro-OMeTAD layer on top of the perovskite, thereby improving the charge carrier collection between these two layers. Upon systematically investigating the layer-by-layer structure of the PSC stack, we discovered that ALD-Al₂O₃ also acts as a diffusion barrier for the degraded species from the adjacent transport layer into the perovskite. In addition to all protection capabilities, ALD-Al₂O₃ impedes the transition of crystalline perovskites to an undesired amorphous phase instead of a yellow delta phase. Consequently, the dual functionality (i.e., enhanced mechanical adhesion and diffusion barrier) of the ALD-Al2O3 protection enhanced the device performance from 19.1% to 20.5%, retaining 98% of its initial power conversion efficiency compared to <10% for pristine devices after 1500 h of outdoor testing under ambient conditions. Finally, this study deepens our understanding of the mechanism of ALD-Al₂O₃ as a two-way diffusion barrier, highlighting the multifaceted role of buffer layers in interfacial engineering for the long-term stability of PSCs.