Unraveling segregation behavior of inactive secondary phase driven by ion-competition reaction for perovskite-2D PbI2 heterojunction solar cells.

The undesired segregation of inactive secondary phase that randomly distributed across the perovskite film is detrimental to charge-carrier transport dynamics and light stability. However, in-depth studies for understanding the underlying chemical reaction mechanism and the relationship between phase structural configuration and physical properties are still lacking. Herein, the segregation behavior of the inactive secondary phase and the underlying microcosmic mechanism regarding ionic chemical replacement reaction and lattice reconfiguration process are systematically elaborated. A high-quality perovskite-PbI 2 heterojunction film is constructed via converting the three-dimensional PbI 2 photoactive phase into a two-dimensional inactive phase, alleviating the energetic disorder of carrier dynamics and photochemical dissociation. The resultant perovskite solar cells achieve an efficiency of 24.23% with excellent light-resistance. The dissociation energetics of phase dimensional structure is theoretically analyzed. This work provides new insights into crystal structure design for constructing high-quality perovskite heterojunction devices. [Display omitted] • The segregation behavior of secondary phase in perovskite is rationally regulated based on dimensional engineering strategy. • Evolution mechanism of ion-competition reaction and lattice reconstruction process is revealed in depth. • The energetic disorder of carrier dynamics is well ameliorated based on the formed build-in type-Ⅰ band alignment. • Perovskite-2D PbI 2 heterojunction devices achieve high efficiency of 24.23% with excellent long-term light-resistance. [ABSTRACT FROM AUTHOR]