The integration of 2D materials into future applications relies on advances in their quality and production. We here report a synthesis method that achieves ultrahigh optoelectronic performance at unprecedented fabrication scales. A mediator-assisted chemical vapor deposition process yields tungsten-disulfide (WS2) with near-unity photoluminescence quantum yield, superior photosensitivity and improved environmental stability. This enhancement is due to the decrease in the density of lattice defects and charge traps brought about by the self-regulating nature of the growth process. This robustness in the presence of precursor variability enables the high-throughput growth in atomically confined stacks and achieves uniform synthesis of single-layer WS2 on dozens of closely packed wafers. Our approach enhances the scientific and commercial potential of 2D materials as demonstrated in producing large-scale arrays of record-breaking optoelectronic devices.