The Thermomechanical Properties of Thermally Evaporated Bismuth Triiodide Thin Films

Abstract

Abstract Bismuth triiodide (BiI 3 ) has been studied in recent years with the aim of developing lead-free semiconductors for photovoltaics. It has also appeared in X-ray detectors due to the high density of the Bismuth element. This material is attractive as an active layer in solar cells, or may be feasible for conversion into perovskite-like material (MA 3 Bi 2 I 9 ), being also suitable for photovoltaic applications. In this study, we report on the thermomechanical properties (stress, hardness, coefficient of thermal expansion, and biaxial and reduced Young’s moduli) of BiI 3 thin films deposited by thermal evaporation. The stress was determined as a function of temperature, adopting the thermally induced bending technique, which allowed us to extract the coefficient of thermal expansion (31 × 10 −6 °C −1 ) and Young’s biaxial modulus (19.6 GPa) for the films. Nanohardness (~0.76 GPa) and a reduced Young’s modulus of 27.1 GPa were determined through nanoindentation measurements.