Formamidinium lead iodide (FAPbI₃) has become one of the most promising materials for high performance perovskite solar cells (PSC_s) with its ideal band gap and broad light absorption spectrum. However, the traditional solution-processed FAPbI₃ layer usually have low crystallinity with the existence of the photoinactive δ-FAPbI₃with the isotropic low quality α-FAPbI₃ resulting in limited stability. Moreover, unavoidable structural defects will form during crystallization could associate with a variety of drawbacks including severe ion migration and bleaching in PSCs. Here, we introduced the thiol (3-Mercaptopropionic acid, 3-MPA) functionalized molybdenum disulfide (MoS₂) nanoflakes (NFs) into the FAPbI₃ perovskite layer. The MPA-MoS₂ NFs are incorporated through mixing with FAPbI₃ precursors when preparing the ink. The NFs are believed to severe as the crystallization agent and passivates the defects in the as-prepared films. We tracked the crystallographic evolution during thermal annealing with synchrotron-based in situ grazing-incidence wide angle (GIWAXS). The result shows that the MPA-MoS₂ forms an intermediate structure with FAI at the initial stage then facilitate the orientated growth of FAPbI₃. Moreover, as observed in SEM and XRD, respectively, the MPA-MoS₂ incorporated FAPbI₃ shows increases in average grain size with a 3-fold enhancement in crystalline peak intensity, suggesting the promotion of the perovskite crystal quality after the incorporation of the NFs. In addition, as witnessed in photoluminescence (PL) and lifetime decay measurements, the FAPbI₃ with MPA-MoS₂ NFs functionalized by monolayer of the MPA thiols exhibits quenching in PL intensity and lifetime, indicating more efficient the charge transport likely occurs in the NFs incorporated FAPbI₃.

Yifan Yin

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