Intermediate Phase Engineering with 2,2-Azodi(2-Methylbutyronitrile) for Efficient and Stable Perovskite Solar Cells

Sequential deposition has been widely employed to modulate the crystallization of perovskite solar cells because it can avoid the formation of nucleation centers and even initial crystallization in the precursor solution. However, challenges remain in overcoming the incomplete and random transformation of PbI₂ films with organic ammonium salts. Herein, a unique intermediate phase engineering strategy has been developed by simultaneously introducing 2,2-azodi(2-methylbutyronitrile) (AMBN) to both PbI₂ and ammonium salt solutions to regulate perovskite crystallization. AMBN not only coordinates with PbI₂ to form a favorably mesoporous PbI₂ film due to the coordination between Pb²⁺ and the cyano group (C≡N), but also suppresses the vigorous activity of FA⁺ ions by interacting with FAI, leading to the full PbI₂ transformation with the preferred orientation. Therefore, perovskites with favorable facet orientations are obtained, and the defects are largely suppressed owing to the passivation of uncoordinated Pb²⁺ and FA⁺ . As a result, a champion power conversion efficiency over 25% with a stabilized efficiency of 24.8% is achieved. Moreover, the device exhibits an improved operational stability, retaining 96% of initial power conversion efficiency under 1000 h continuous white-light illumination with an intensity of 100 mW cm^-2 at ≈55 °C in N₂ atmosphere.