Adjusting stability of FAPbI3 solar cells via phase-controlled single crystal precursors

To achieve high efficiency in α-FAPbI3-based perovskite solar cells, an effective strategy involves utilizing defect-minimized single-crystal FAPbI3 as a precursor for thin-film fabrication. However, the phase stability of freshly synthesized α-FAPbI3 single crystals (fresh-α-FAPbI3) is strongly affected by storage conditions. When stored in an open environment, the single crystal retains its pristine black α-phase (open-α-FAPbI3). Conversely, storage in a sealed environment induces a phase transition to the yellow δ-phase (sealed-δ-FAPbI3). In this study, three distinct single-crystal phases were employed as precursors for perovskite solar cells to systematically evaluate their long-term stability concerning crystal phases. The crystallinity and carrier lifetime of the resulting thin films were monitored over the course of one month. The results revealed that using fresh-α-FAPbI3 as a precursor maintained superior crystallinity and suppressed carrier recombination. Additionally, variations in the work function of the films were investigated. Stability assessments demonstrated that devices fabricated using fresh-α-FAPbI3 exhibited remarkable resilience, retaining 97.68% of their initial efficiency after one month. These findings highlight the role of the single-crystal phases in bolstering the operational stability of perovskite solar cells and underscore the necessity of further exploration into phase transitions under different storage conditions.