Nanocrystalline CsPbBr3 thin films: a grain boundary optoelectronic study

Recently ternary compounds of CsPbX3 (X=Cl, Br, I) produced by co-evaporating CsX and PbX2 purified powders are attracting much interest for their interesting optical characteristics and potential applications in luminescence based detector and devices. Indeed, nano-crystallites are produced in the thin film material as evidenced by optical spectroscopy and X-Ray diffraction. These ternary nano-aggregates are wide-gap semiconductors with direct band-to-band transition. Identification of the nano-crystallites in the film is based on a similarity of the observed spectroscopic properties with those of the bulk CsPbX3 purified by the Bridgman technique. The materials object of this study have been deposited by Physical Vapour Deposition inside an UHV apparatus on DC7059 optical glass starting from CsBr and PbBr2 purified powders or by crushing Bridgman crystals. In this paper, we report on an impedance spectroscopy study in a wide frequency range (10-5 107 Hz) and temperature (100-650 K) aimed to identify the distribution of surface related electronic defects. Moreover, transient photoconductivity measurements in the sub-nanosecond range have then been performed to infer the role of these defects on the charge carriers recombination mechanism and mobility-lifetime product.