Unveiling the Mutual Promotion Mechanism of Adjacent Vacancy Defects Enables High-Performance Perovskite Solar Cells.

The perovskite defect evolution directly impacts the efficiency and stability of perovskite solar cells (PSCs). In this work, the mutual promotion mechanism of adjacent cation and anion vacancies in perovskite is unveiled, which means the cation/anion vacancy induces the adjacent anion/cation vacancy through decreasing the formation energy. This mutual promotion mechanism provides an explanation for the dynamic evolution of defects, and emphasizes the necessity of simultaneously passivating of adjacent defects. Accordingly, a new additive of 2-hydrazinylpyrazine is utilized to passivate adjacent defects, considering its adjacent electron-rich N atom, which can chemically bond uncoordinated Pb, and the hydrazine group, which can anchor FA+ through hydrogen bonds. Besides, this 2-hydrazinylpyrazine also optimizes the perovskite crystallization through accelerating nucleation and slowing crystal growth, demonstrated by the in situ photoluminescence spectra. The resulting inverted 0.08 cm2 and 1 cm2 PSCs obtain PCEs of 26.28% and 24.71%, respectively. Moreover, the Target device shows enhanced stability by maintaining 93% and 90% of the initial efficiency after operating 1700 h under 1-sun illumination and being exposed to harsh thermal cycling for 150 times, respectively.