Morphology of X-ray detector Cs₂TeI₆ perovskite thick films grown by electrospray method

For the purpose of developing Cs₂TeI₆ based X-ray detectors and imaging devices, Cs₂TeI₆ thick films were prepared using the electrospray method under ambient conditions. The effects of spraying parameters on the morphology of the films were investigated. During the electrospray process, we observed that Cs₂TeI₆ microdroplets changed to a steady cone jet and then to an unstable multi-jet model as the electrical bias increased from 6 kV to 12 kV, resulting in variable film morphologies. Five representative solvent systems with different evaporation rates and contact angles on the FTO/double-TiO₂ substrates were studied. We find a strong correlation of the contact angle with the speed of primary nucleation, growth mode and subsequent film morphology. Moreover, the crystalline quality has been improved with the rise of substrate temperature. Finally, a dense and uniform Cs₂TeI₆ film was obtained with an electrical bias of 10 kV using dimethyl formamide (DMF) as the solvent at a substrate temperature of 160 °C. The resulting Cs₂TeI₆ films have resistivity on the order of 10¹⁰ Ω cm, which indicates potential applications in X-ray detection and imaging. The films show a strong photoresponse to visible light based on the Cs₂TeI₆ thick film devices, and an on-off ratio of 22 under 425 nm light (∼65 mW cm^-2). The sensitivity of the assembled Cs₂TeI₆ perovskite-based detectors can be 2.4 nC R^-1 cm^-2 under illumination of 60 kVp X-rays.