Stretchability and permeability of amorphous alumina-based nanolaminates for encapsulation of perovskite solar cell

Abstract

Perovskite solar cells must be coated with materials that are low moisture permeability due to moisture degradation. Amorphous structure aluminum oxide (Al2O3) films are used for various applications such as gas- and moisturediffusion barriers. Al2O3 films deposited by atomic layer deposition (ALD) have good step coverage, high density and low surface roughness. However, these films contain more impurities and need longer processing time at lower growth temperatures. By Griffith’s theory, the fracture strength of brittle materials increases with decreasing thickness and reaches an ideal strength at a critical thickness. Also, metallic glass-metal nanolaminate composites had different mechanical behavior from metallic glass single layer, as reported by several authors: metal layers suppressed catastrophic failure of metallic glass. So here we look at the critical thickness of amorphous Al2O3 films deposited by ALD at low temperature (<100℃), which are brittle materials, and the changes in the mechanical behavior of amorphous Al2O3 when it is laminated with the inorganic material. We analyzed effect of temperature and thickness on mechanical properties and found the critical thickness of Al2O3 film. We then made amorphous Al2O3-inorganic nanolaminate composites and measured mechanical properties by tensile testing by an in-situ system. Also we measured water vapor transmission rate (WVTR) of Al2O3 single layer and nanolaminate composites using calcium test and evaluated performance as an encapsulation.