Unveiling and Overcoming Instabilities in Perovskite Solar Cells Induced by Atomic-Layer-Deposition Tin Oxide

Atomic layer deposition of tin oxide (ALD-SnOx) has emerged as a promising buffer/protection layer, often replacing bathocuproine (BCP) in applications such as semitransparent and tandem devices. However, the long-term stability and underlying degradation mechanisms of perovskite solar cells (PSC) incorporating ALD-SnOx remain elusive. Herein, the long-term stability of PSCs featuring an ALD-SnOx buffer layer is systematically investigated. Intriguingly, it is observed that cells with ALD-SnOx exhibit heightened susceptibility to severe degradation, surpassing even the degradation levels observed with BCP under humid conditions. Through an extensive analysis employing X-ray photoelectron spectroscopy and X-ray diffraction, it is unveiled that ALD-SnOx triggers a phase transition in the perovskite when exposed to moisture, transitioning from the black cubic phase to the yellow delta phase, despite the presence of a thin layer of fullerene between the SnOx and the perovskite. Replacing ALD-SnOx with ALD-AlOx as a buffer layer emerges as a transformative strategy, effectively bolstering the humidity and thermal stability of the cells, without affecting device efficiency. The optimized ALD-AlOx-buffered device exhibits a high efficiency of 24.61% and maintains 88% of its initial efficiency after maximum power point tracking under 1 sun illumination for 1350 h at 65 degrees C in ambient air when encapsulated. The stability of perovskite solar cell devices, utilizing atomic layer deposition tin oxide (ALD-SnOx) buffer layers, is investigated. A critical degradation pathway in ALD-SnOx-based devices under humidity stress is uncovered. Substituting ALD-SnOx with ALD-AlOx results in excellent stability in the devices, a T90 of over 1000 h is demonstrated at 65 degrees C in ambient air.image (c) 2024 WILEY-VCH GmbH