Regular Article

Effect of annealing on photo-physical properties of BiI₃ thin films via vacuum thermal evaporation deposition for photovoltaic applications

¹ Department of Physics, Yazd University, Yazd, Iran
² Photonics Research Group, Yazd University, Yazd, Iran

^* e-mail: abehjat@yazd.ac.ir

Received: 9 December 2022
Received in final form: 24 January 2023
Accepted: 31 January 2023
Published online: 26 April 2023

Abstract

In this paper, a simple thermal evaporation deposition (TED) method is used to obtain high-quality bismuth triiodide (BiI₃) films on FTO substrate using BiI₃ powder as an evaporation source. The effects of annealing on the X-ray diffraction analysis and some optical parameters of BiI₃ thin films were investigated. The results show that the annealing temperature on the BiI₃ thin film has a great influence on the preferred orientation of the films. When the annealing temperature is 100 °C, for a deposition thickness of 400 nm, the thin films have high crystallinity and rhombohedral morphology. Scanning electron microscopy observation showed high special resolution of BiI₃ thin films. UV–Vis transmission spectra have been recorded to determine the optical band-gap of BiI₃ films prepared by TED. The obtained data reveal that the indirect optical band-gap of BiI₃ thin films decreases from about 1.7 to 1.6 eV, while the Urbach tail width decreases from 484 to 236 meV, by annealing. We discuss the outstanding annealing effect on photo-physical characterizations of BiI₃ thin film as a candidate solar cell absorber such as lead-free perovskite solar cells.