Crystalline Phase Segregation of Quantum-Dots-Passivated CH₃NH₃PbI₃ Film via Argon Plasma Treatment

In this study, a composite perovskite film composed of lead cesium triiodide (CsPbI₃) quantum dots (QDs) and methylammonium lead iodide (CH₃NH₃PbI₃; MAPbI₃) was proposed. The CsPbI₃ QDs prepared by hot-injecting were used as an anti-solvent in precursors to passivate the surface of this composite perovskite film. The further argon (Ar) plasma treatment improves the surface of the film. The effects of the powers from 100 to 200 W on the composite perovskite film structure, chemical element composition, and optical properties were studied. The experimental results demonstrate that the CsPbI₃ QDs passivation boosts the ultraviolet light absorption (350–450 nm) and inhibits the formation of the PbI₂ phase. Furthermore, Ar plasma treatment effectively improved CsPbI₃ QDs passivation on MAPbI₃ film. The powers lower than 140 W cause C=O bonds to dissolve and coordination bonds to form between OA carboxyl moieties and undercoordinated Pb²⁺ ions. At 160 and 140 W, the obvious crystal phase segregation and a decrease in light absorption are observed, respectively. Meanwhile, the strong bombardment of Ar ions at higher than 160 W causes the severe degradation of MAPbI₃ film.