Layered transition metal chalcogenides (TMDCs) are promising materials for developing multifunctional and compact optoelectronic-integrated devices to extend Moore's Law. However, the low photoluminescence quantum efficiency (PLQY) and single carrier polarity remain two bottlenecks in achieving these exciting applications, due to the notorious defects that unavoidable in the sample preparation.Here, we report a unique defect engineering strategy from both theoretical and experimental perspectives, and achieve simultaneously giant photoluminescence enhancement and carrier polarity modulation in WS₂ monolayers via doping with IIIA atoms. The doped samples exhibit large sizes (~614 µm), significantly improved PL quality with the PL intensity/PLQY being up to two orders of magnitude higher than that of undoped ones, and simultaneous carrier polarity modulation from unipolar to ambipolar. Moreover, the constructed p-n homojunctions based on the doped samples show excellent rectification ratio (up to ~2200) and ultra-fast response time (<1 ms). Intriguingly, both the PL property and device performance display extraordinary stability even after hundreds of days under the atmospheric environment. Our doping strategy is universally applicable to other TMDCs and dopants. This work not only provides a general strategy to eliminate the negative effects of defects in 2D materials, but also utilize them to achieve desired optoelectronic properties by smart design, marking an important step toward multifunctional and high-performance optoelectronic-integrated devices and systems.