CH₃NH₃PbI_3–xCl_xunder Different Fabrication Strategies: Electronic Structures and Energy-Level Alignment with an Organic Hole Transport Material

We report a photoelectron spectroscopy study on the electronic structure of CH 3 NH 3 PbI 3– x Cl x thin films fabricated by physical evaporation from CH 3 NH 3 I and PbCl 2 precursors, including (1) simultaneously evaporation and (2) sequential evaporation. The results are compared with CH 3 NH 3 PbI 3– x Cl x made using conventional solution chemistry (i.e., spin-coating). Depending on the fabrication method, CH 3 NH 3 PbI 3– x Cl x films show different chemical constituents in the near-surface region, leading to disparities in their energetic levels. The chemical identities of the surface species are revealed by an in situ study on the sequentially evaporated film. Moreover, air-exposure treatment also greatly alters the energetic levels of the film. Using hole transport layer of N, N ′-di(1-naphthyl)- N, N ′-diphenylbenzidine (NPB) as a model system, we find that the energy-level alignment with the spin-coated film after air exposure is most suitable for efficient hole transport.