Abstract
Bismuth triiodide (BiI3) 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 (MA3Bi2I9), 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 BiI3 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.
Highlights
The current demand for cost-efficient and renewable materials for energy applications has recently acted as a great driving force towards the development of low cost photovoltaic cells
Podraza et al.[6], who determined that a single BiI3 crystal has an indirect band gap of 1.67 eV
The latter reached this value after several measurements aimed at solving discrepancies found in the literature, which varied from a direct band gap of 2.2 eV21 to an indirect one of 1.55 eV6
Summary
The current demand for cost-efficient and renewable materials for energy applications has recently acted as a great driving force towards the development of low cost photovoltaic cells. With a view to overcoming this issue, some lead-free materials suitable for photovoltaic applications have gained the attention of researchers in recent years In their studies, bismuth triiodide (BiI3)[2,3,4,5] has revealed itself to be a promising candidate for photovoltaic applications, being a semiconductor with an adequate band gap for these purposes: 1.67 eV6. Bismuth triiodide (BiI3)[2,3,4,5] has revealed itself to be a promising candidate for photovoltaic applications, being a semiconductor with an adequate band gap for these purposes: 1.67 eV6 This material is versatile, and useful as the active absorbent layer in solar cells; it may be suitable for conversion into a perovskite-like material such as MA3Bi2I9, which is suitable for photovoltaic applications[7,8,9]. (c) Refractive index and extinction coefficient as a function of photon energy (the inset is a photo of a sample −25 mm × 5 mm in size). (d,e) Scanning electron microscope images of top view and cross section of BiI3 films, respectively and (f) AFM image
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