Not yet reviewed by Pith; the record is open.

Silver phenylselenide (AgSePh), known as mithrene, is a two-dimensional (2D) organic-inorganic chalcogenide (MOC) semiconductor with a wide direct band gap, narrow blue emission and in-plane anisotropy. However, its application in next-generation optoelectronics is limited by crystal size and orientation, as well as challenges in large-area growth. Here, we introduce a controlled tarnishing step on the silver surface prior to the solid-vapor-phase chemical transformation into AgSePh thin films. Mithrene thin films were prepared through thermally assisted conversion (TAC) at 100{\deg}C, incorporating a pre-tarnishing water (H${_2}$O) vapor pulse and propylamine (PrNH${_2}$) as a coordinating ligand to modulate Ag${^+}$ ion reactivity and facilitate the conversion of Ph${_2}$Se${_2}$ into an active intermediate. The AgSePh thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and grazing incidence wide-angle X-ray scattering (GIWAXS). The pre-tarnishing process, combined with organic ligands, resulted in large crystals exceeding 1 ${\mu}$m and improved homogeneous in-plane orientation, while also enabling the selective, wafer-scale synthesis of mithrene on 100 mm wafers. Furthermore, the films were integrated on planar graphene field-effect phototransistors (GFETs) and demonstrated photoresponsivity beyond 100 A/W at 450 nm, highlighting mithrene's potential for blue light-detection applications.