Critical Layer Thickness for Epitaxial FAPbBr_xI_3-x on KCl (001)

The development of solar cells using mixed organic-inorganic perovskite materials requires the epitaxial deposition of thin films on large-area, lattice-mismatched substrates. It is therefore important to understand the effects of lattice mismatch, elastic strain, and lattice defects on device performance. In this paper, we have conducted a preliminary investigation to estimate the critical layer thickness for lattice relaxation in FAPbBr_xI_3-x alloys deposited epitaxially on KCl (001) substrates. The critical layer thickness exceeds 10 nm in the vicinity of 2.2 < x < 2.8, but is strongly dependent on x as well as growth temperature, so the achievement of stable, coherently-strained epitaxial layers will require tight control of the composition and uniformity.