Cu ion substitution induced grain growth, band gap engineering and carrier recombination engineering of all-inorganic CsPbBr₃ perovskite films

All-inorganic CsPbBr₃ perovskite films with the different degrees of Cu ion substitution were prepared by multi-step spin coating precursor solutions. Based on the results of XRD and XPS, it was confirmed that partial Pb was replaced by Cu and no impurities were generated with the increase of Cu content in the Cu-doped CsPbBr₃ film. The red shift of the diffraction peak and the decrease of lattice constant in the range of 0%-3% Cu ions in this XRD spectra demonstrate the progressive substitution of Cu ions, which suggests lattice contraction. It was seen that the average grain size significantly increased to 841.94 nm with the addition of 3% Cu into CsPbBr₃ films from SEM. Meanwhile, the optical band gap of the CsPbBr₃ film decreases to 2.336 eV and the recombination probability of carriers of the CsPbBr₃ film is lower when the Cu ion content gradually increases to 3%. However, the average grain size reduces, the optical band gap increases, and the recombination probability of carriers improves as the Cu ion content gradually increases to 6%. Therefore, the content of optimal Cu ion is 3% in this experiment. This work provides a new path for the development of all-inorganic perovskite films and devices.