Synergetic Phase Modulation and N-Doping of MoS₂ for Highly Sensitive Flexible NO₂ Sensors

Molybdenum disulfide (MoS₂) is a promising electronic material owing to its excellent electrochemical features, high carrier mobility at room temperature, and widely tunable electronic properties. Here, through precursor engineering and post-treatments to tailor their phase and doping, electronic characteristics of MoS₂ are significantly modified. It is found that 2H semiconductor phase with nitrogen doping (N-doping) in flexible gas sensors constructed with Ag electrodes exhibits the highest sensitivity of ≈2500% toward 10 ppm of NO₂. This sensitivity is ≈17- and 417-folds higher than that of 2H MoS₂ without N-doping, and mixed phases with metallic 1T and semiconductor 2H phase, respectively. Comprehensive experimental investigations reveal mechanisms underlying this record sensitivity, that is, the use of N-doped 2H MoS₂ sensors not only significantly suppresses dark current but also effectively enhances electron transfer to NO₂ molecules. Moreover, density function theory calculations underpin the experimental results, confirming that N₂H₄ molecules from the precursor solution not only promote phase transition but also enable N-doping during post-treatments, thus boosting sensing capability. This work, for the first time, reveals the synergistic effect of phase modulation and N-doping of MoS₂, which can be readily used in other flexible electronic applications, advancing MoS₂-based electronics to a new stage.