Halide perovskites have gained interest as light absorber materials due to their outstanding properties for optoelectronic devices, including record efficiencies in solar cells and ignited research in photodetectors. However, the challenges remain unresolved, including the inherent instability of hybrid perovskite materials and the formation of intermediate phases during solvent-based synthesis methods. To overcome these challenges, we developed the mechanosynthesis (MS) of hybrid perovskite powders and perovskite-graphite composites for visible light photodetector applications. Using this scalable and solvent-free ball-milling technique, we synthesized methylammonium lead iodide (MAPbI₃) hybrid perovskites and MAPbI₃-graphite composite powders, and characterizations have shown that nanograins (∼10 nm) in aggregates share common crystallographic orientations [1]. The synthesized composites were designated as MAPI-4h (without graphite), MAPI-Gr3%, and MAPI-Gr5%, with high yields of 86.3%, 84.3%, and 89%, respectively. The obtained powders were compacted into pellets via uniaxial compaction, and Ag electrodes were deposited on top of pellets to fabricate photodetector devices. The devices were designated as Ag-MAPI-4h, Ag-MAPI-Gr3%, and Ag-MAPI-Gr5%, respectively. The formation of ohmic contact was verified by stable linear current-voltage (I-V) curves in the dark. With the addition of Ag electrodes, the devices exhibited ten times higher current and more efficient charge extraction compared to pellets without Ag electrodes. An uniform distribution of few-layer graphite within the MAPbI₃ matrix was noticed in pellets. The effect of graphite addition was also studied for improving the photodetection performance. The Photoresponsivity was measured around 750 nm wavelength. The photoresponsivity of Ag-MAPI-Gr5%, Ag-MAPI-Gr3%, and Ag-MAPI-4h were respectively 0,13 ⅹ 10⁶ AW^-1, 7,7 ⅹ 10⁰ AW^-1, and 58,87 ⅹ 10^-3 AW^-1. Fast rise time (τ_r) and fall time (τ_f) were recorded for Ag-MAPI-4h as 1.1 s and 1.68 s, respectively, under light. Graphite should enhance the conductivity and hence the charge transport; however, it diminishes the photoresponsivity. Graphite-enhanced Raman scattering was observed with the composite with 5 wt % graphite, showing its strong resistance to photodegradation and suggesting a charge transfer between graphite and MAPbI₃. Such charge transfer is also in agreement with the quenching of the PL with an increasing amount of graphite. The presence of graphite would induce a local modification of the Coulomb interaction, “attracting” the charge carriers at the graphite and MAPbI₃ interfaces and thus favoring the charge separation and transport. This high photoconductive gain matches with the trapping of one type of charge carrier, while the other one is multiplied via injection from the contact electrodes, thus contributing even more to the photoconductivity. These results demonstrated at first the great potential of mechanosynthesis, which is a green, easy scalable and eco-friendly powder synthesis technique to develop light-sensitive materials for photovoltaic and photodetection applications.

Keywords : Mechanosynthesis of perovskites, MAPbI₃@Graphite composites, visible-light photodetectors, solvent-free synthesis, perovskite photodetectors