Improving Stability and Performance of Cesium Mixed Lead Halides for Photovoltaic Applications

Abstract We have focused on mixed halide perovskite thin films of the formula CsPbX 3 where (X 3 = Br 3 , Cl 3 , I 3 , Br 2 Cl, Br 2 I, and I 2 Cl) prepared by spin-coating in order to study the effects of partial and total Br substitution. For this purpose, we performed a series of characterizations, including x-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–visible spectroscopy. All the films except CsPbI 2 Br showed two characteristic peaks at 2 θ angles of 26.80° and 51.80° corresponding to the (111) and (220) crystallographic planes. In the case of CsPbI 2 Br, we have the same peaks, but the main ones are located at 15° and 30° for the (100) and (200) planes, respectively. SEM examined the surface morphology of the different mixed lead halide films; the best surface was that of the CsPbBr 2 I sample, which is well-coated, dense, with no pinholes and no cracks, and has the largest grain size. In addition, all the mixed halide films showed good absorbance, especially between 600 nm and 900 nm, with band gap values between 1.94 and 2.92 eV.