Wafer-Scale Bandgap-Tunable MoS₂/PbS Phototransistors Enabled by Solution Processing

Molybdenum disulfide (MoS₂)/lead sulfide (PbS) heterostructures exhibit exceptional potential because of their strong light-matter interactions and high carrier mobility. Critically, bandgap engineering can further optimize the light-absorption range for next-generation phototransistors. However, the bandgap engineering capability for MoS₂/PbS heterojunctions formed by conventional transfer-after-chemical vapor deposition (CVD) fabrication is typically inherently restricted due to solely vertical interlayer coupling. Here, to realize wafer-scale bandgap-tunable MoS₂/PbS phototransistors, we investigate the band structure of vertical and lateral MoS₂/PbS heterojunctions via ab initio calculations and find that lateral heterojunctions in heterostructures dominate the bandgap tunability via tuning of the Type-II band alignment. To achieve wafer-scale uniformity, we investigated how plasma treatment modulates the thin-film surface energy, and the results substantially improved fabrication scaling of MoS₂/PbS heterojunctions from traditional micro-scale level to an incredible 4-inch wafer-scale with near-ideal yields (97%) and enabled bandgap tunability (from 1.24 to 0.61 eV). The resulting phototransistors exhibit a maximum responsivity of 88 A/W, specific detectivity of 4.77  ×  10¹² Jones, and a typical on/off ratio of 3.16  ×  10⁷. This work establishes a pathway for developing wafer-scale bandgap-tunable optoelectronics.