Evaluation of the effect that the substitution of the ion MA by the ion Cs produces on the properties of thin films of CsxMA1-xPbI3 prepared by spin-coating

In this paper we report results concerning the effect that the substitution of the ion methylamonium (MA) by the ion cesium causes on the properties of the hybrid compound CsxMA1-xPbI3, synthesized by spin coating. It was found that this substitution occurs effectively when less than 15% of the ions of MA are replaced by cesium and that above this quantity the cesium forms another compound. Special emphasis was placed on evaluating the effect of the Cs content on the optical, structural and morphological properties of CsxMA1-xPbI3 films, through characterization performed using techniques such as diffuse reflectance, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). These studies allowed checking that the incorporation of cesium in the structure of the compound MAPbI3 induces structural disorder, as well as an increase of its energy gap Eg, from a value of 1.56 eV for samples of composition MAPbI3 to a value of 1.59 eV for samples with composition Cs0.25MA0.75PbI3. Additionally, it was found that the CsxMA1-xPbI3 films exhibits a morphology consisting of compact grain with sub-micron size, grouped in needle-shaped structures.