Influence of anion hardness in (001) surface of CsPbX3 (X = F, Cl, Br and I) halide perovskites

Computational simulations play a significant role in material science, determining material properties, developing new materials, and unveiling their technological applications, including studying halide perovskites. This family of compounds is considered promising for use in photovoltaic cells and light-emitting devices. Understanding surface-dependent properties at the nanoscale is crucial because they can differ significantly from those observed on the macroscale. Taking into this account, the present study utilized DFT/HSE06 approach to elaborate a computational model of CsPbX3 (X = F, Cl, Br, and I) compounds and their (001) surfaces. This research found that anion X− hardness strongly influences surface stability, cluster distortions, band gap energy, and carrier mobility. PbX2 surface termination is most stable when X = F, while CsX termination is most stable when X = Cl, Br, and I. According to the anion hardness decrease, outermost clusters in CsX terminations become distorted, and an inverse behavior is observed for PbX2 terminations. The CsPbX3 (001) surfaces exhibit a direct band gap at the R point, characterized by a significant concentration of electronic states below the Fermi level. Furthermore, it has been observed that the anion hardness is crucial to the availability of bands near the band gap, with a decrease in hardness increasing in available electronic states. The band gap energy (Egap) of PbX2 is slightly larger than that of CsX terminations. In the outermost layers for CsX terminations, significantly larger areas of negative potential occur than the PbX2. These results provide valuable insights into designing and optimizing nanoscale halide perovskites for various applications.