Mapping structural properties of lead halide perovskites by scanning nanofocus x-ray diffraction (Conference Presentation)

Abstract

To date, the most widely employed technique to investigate the crystal structure and morphology of perovskite films have been SEM and X-ray diffraction. Most perovskite films are highly polycrystalline and thus traditional imaging techniques cannot easily isolate single crystallites or determine the statistics of lateral grain size or crystal size and morphology. A further limitation is that both SEM and other scanning probe microscopy techniques are surface-sensitive, with the bulk of the material being largely inaccessible using conventional imaging methods. To gain better insight into a perovskite film, we scan an X-ray beam focused to 400 nm across a sample, while simultaneously recording wide-angle X-ray scattering patterns. Such scanning nanofocus x-ray diffraction (nXRD) techniques have been employed to resolve local variations in structure across a broad range of materials and research fields, however this is the first time they have been applied to a perovskite film. We describe a method to in which each scattering pattern is analysed, allowing a classification to be made of individual perovskite grains according to a specific Miller plane. Using this method, we show that nXRD is able to resolve the extent of individual perovskite grains buried within a polycrystalline film (grain segmentation). We then use nXRD and SEM to demonstrate that the perovskite film coverage can be controlled by varying the temperature of the substrate during spin-coating. We conclude by showing that solar cells with a perovskite layer cast on a substrate held at a relatively high temperature result in devices with higher PCE.