In situ crystallization of 0D perovskite derivative Cs3Bi2I9 thin films via ultrasonic spray

Abstract

Cs3Bi2I9 has been proposed to be an alternate candidate for various optoelectronic applications to meet the stability and toxicity issues associated with the highly performing organic lead halide perovskites. In the present work, we report the in situ formation of cesium bismuth iodide thin films by ultrasonically assisted sequential spray deposition of BiI3 and CsI in ethanol-based precursor solutions. The films formed by varying the layer configurations and relative molarity were investigated to identify the optimum conditions to obtain pure Cs3Bi2I9 films. Further, we probe their structure, morphology, optical and electronic properties in combination with computational studies. X-ray diffraction and Raman spectroscopy confirmed the crystallinity and chemical structure of the spray cast perovskite films. Scanning electron microscopy images present the surface morphology composed of uniformly distributed hexagonal grains of ∼ 280 nm in average size. The absorption coefficient of the films was evaluated in the order of ~ 106 cm−1 using UV–Vis–NIR spectral analysis. The calculated direct band gap value of 1.99 eV was in accordance with the theoretical calculations. Furthermore, the optimized Cs3Bi2I9 film was photoconductive. The I-V characteristics of FTO/ZnO/Cs3Bi2I9/C-Ag heterojunction revealed a significant rectification behavior with a diode factor of 1.75. FTO/CdS/Cs3Bi2I9/C-Ag heterojunction showed a Voc of 300 mV and Jsc of 0.003 mA cm−2. Our results imply that the spray deposited Cs3Bi2I9 films have a profound potential for applications in photodetectors and solar cells upon detailed investigations.