Low-Temperature Atomic Layer Deposition of Metal Oxide Layers for Perovskite Solar Cells with High Efficiency and Stability under Harsh Environmental Conditions

Rapid progress achieved on perovskite solar cells raises the expectation for their further development toward practical applications. Moisture sensitivity of perovskite materials is one of the major obstacles which limits the long-term durability of the perovskite solar cells, especially in outdoor operation where rainfall and water accumulation on the solar panels often occur. Micro/nanopinholes within the functional layers of the devices usually lead to water vapor penetration, thus subsequent decomposition of perovskites, and finally poor device performance and shortened operational lifetime. In this work, low-temperature atomic layer deposition (ALD) technique was utilized to incorporate pinhole-free metal oxide layers (TiO₂ and Al₂O₃) into an inverted perovskite solar cell consisting of indium tin oxide/NiO/perovskite/PC₆₁BM/TiO₂/Ag. The interface properties between the inserted TiO₂ layer and the perovskite layer were investigated by X-ray photoelectron spectroscopy. The results showed that TiO₂ ALD fabrication process had made negligible degradation to the perovskite layer. The TiO₂ layer can significantly reduce interfacial charge recombination loss, improve interfacial contact, and enhance water resistance. A maximum power conversion efficiency (PCE) of 18.3% was achieved for devices with TiO₂ interface layers. A stacked Al₂O₃ encapsulation layer was designed and deposited on top of the devices to further improve device stability under harsh environmental conditions. The encapsulated devices with the best performance retained 97% of the initial PCE after being stored in ambient condition for a thousand hours. They also showed great water resistance, and no significant degradation in terms of PCE and photocurrent of the devices was observed after they were immersed in deionized water for as long as 2 h. Our approach offers a promising way of developing highly efficient and stable perovskite solar cells under real-world operational conditions.