Atomic layer deposition of Al2O3 on CH3NH3PbI3 for enhancement of perovskite solar cells stability

Organic-inorganic perovskites like methylammonium lead triiodide (CH3NH3PbI3) films represent a new paradigm for photovoltaics, which have the potential to overcome the performance limits of current technologies and achieve low cost and high versatility.[1-5] Although the power conversion efficiency of the CH3NH3PbI3-based perovskite solar cells exceeded already 21%, a number of key issues must be solved before the widespread commercialization will be possible. Typically, when exposed to the air or moisture hybrid perovskite films degrade within a couple of hours or days.[1, 2] Moreover, the CH3NH3PbI3 perovskite cannot sustain prolonged annealing at temperatures higher than around 85 C.[3, 4] It also undergoes degradation upon applying electric field with the presence of moisture.[5] Improving and controlling perovskite stability along with understanding of degradation pathways are now deeply studied. By understanding how the material properties affect the performance of perovskite solar cells, further improvements for future applications will be possible. The conformal coverage of the CH3NH3PbI3 perovskite film at low temperature with a thin metal oxide layer is very promising to protect it against degradation. The perfectly matching method to fulfill both requirements is the atomic layer deposition (ALD)[6]. In order to prevent thermal degradation of the perovskite a deposition at temperatures lower than 80 C is desirable.In this paper, we present our X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) studies on the ALD growth of Al2O3 on the CH3NH3PbI3 perovskite film at room temperature. TMA and …