Separate observation of surface passivation and linking effects of oleylamine alkylamine ligands on metal-halide perovskite films

In this study, we separately observed the synergetic effects of crystal linking and substituting A-site vacancies with the linker molecule oleylamine (OAm) alkylamine in metal-halide perovskite films by adopting a simple drying process during perovskite structure formation. Furthermore, without the drying process, we observed the synergetic effect of passivation and crystal linking in the OAm films. Owing to the linking effect, the preferred (001) orientational alignment of the crystals improved compared with that of the pristine film. In addition, we evaluated surface passivation using X-ray photoelectron spectroscopy. However, when we applied the drying process before thermal annealing, OAm molecules were observed only in the surface region of the film, and the crystal distribution was similar to that of the pristine film without OAm. Furthermore, when the passivation effect is maximized, significantly improved water resistance and stability were obtained. Despite the initial device performance of the OAm device showed the most improved power conversion efficiency (PCE), the PCE of OAm + Dry device degraded the least due to strongly induced passivation effect. The OAm + Dry maintained 70.4% of their initial PCE after 1000 h without encapsulation in the ambient air, but 58.8% and 16.2% for the OAm and the Control devices.