Hybridized Flat Band-Assisted Photoresponse Enhancement in Superatomic Crystal Mg4C60

The band structure critically determines the intrinsic photodetector performance. With a high density of states (DOS), favorable band configuration, and strong electronic correlations, flat-band physics offers promising perspectives for optoelectronic optimization. Here, we demonstrate a broadband photodetector based on Mg4C60 superatomic crystals, in which hybridization of C-2p and Mg-3s orbitals creates flat bands with a suitable semiconducting gap. Such hybridization produces a global off-Γ conduction band minimum (CBM) with a nearly flat dispersion of ∼50 meV and an indirect quasiparticle gap of ∼1.37 eV, yielding a pronounced photoresponse peak at 905 nm. Complementary optical measurements and theoretical calculations show that these flat bands promote the photodetection figures of merit in few-layer Mg4C60 devices, leading to excellent photoresponsivity of ∼7 A·W-1, detectivity of ∼8.1 × 109 Jones, noise equivalent power of ∼5.5 × 10-14 W·Hz-1/2, and external quantum efficiency of ∼950%, exceeding most carbon-based photodetectors. This work establishes a general strategy for high-performance optoelectronics via flat-band engineering in superatomic crystals.