Trapped Fluorine Enables Thermally Stable Broadband Photodetection in Graphene/Fluorinated Graphene Heterostructure

Fluorinated graphene holds significant promise for optoelectronic applications, yet the instability of carbon–fluorine (C‐F) bonds has limited its practical use. This study investigates the long‐term operational and thermal stability of a photodetector containing graphene/fluorinated graphene heterostructure (Gr/F‐Gr HS). In this design, the top graphene serves as a capping layer that stabilizes fluorine atoms in the bottom fluorinated graphene (F‐Gr) via interlayer interactions and suppresses fluorine diffusion. This fluorine‐trapping configuration effectively passivates the defects in the F‐Gr layer, enhancing both the drain current and optical absorption without altering the device structure. The photodetector achieves > 10 4 A/W responsivity, ≈10 12 Jones detectivity, and sub‐200 µs response, enabling frequency resolution up to 1 kHz across a broad spectral wavelength range (300–1150 nm). The device retains ≈86% of its initial photocurrent after one year in ambient conditions and remains stable up to 200 °C. All‐atom molecular dynamics simulations support the experimental results, revealing that the capping layer stabilizes C‐F bonds by suppressing fluorine migration and enabling interlayer fluorine redistribution. Together, these findings highlight the superior thermal stability of Gr/F‐Gr, reinforcing its promise for advanced optoelectronic applications.