Template-Assisted Growth of High-Quality α-Phase FAPbI₃ Crystals in Perovskite Solar Cells Using Thiol-Functionalized MoS₂ Nanosheets

Formamidinium lead iodide (FAPI) has gained attention for hybrid perovskite solar cell (PSC) applications due to its enhanced stability and narrow bandgap. However, a significant challenge remains in inducing and stabilizing the elusive perovskite "black phase"─photoactive cubic α-FAPI─as the relatively bulky FA⁺ cations tend to favor the thermodynamically stable nonphotoactive "yellow phase". In this study, we present a templated growth strategy employing thiol-functionalized MoS₂ nanosheets as templates. By introduction of 3-mercaptopropionic acid (MPA)-functionalized MoS₂ as a growth template, precise control over crystal formation was achieved, favoring the growth of high-quality α-FAPI films. These advanced templated films exhibited substantial improvements in charge transport properties, efficient light absorption, and enhanced charge extraction. As a result, the PSCs achieved a significantly enhanced power conversion efficiency (PCE) compared to the nontemplated control device, increasing from 20.6 to 22.5%. The MoS₂-incorporated device also demonstrated excellent shelf stability, maintaining 91% of the initial PCE even after 1600 h of storage without device encapsulation.