Compositing　a　secondary　phase　in　Ag2Se　can　usually　tune　the　electron　and　phonon　scattering　to　improve　the　thermoelectric　performance.　However,　the　intrinsically　high　carrier　concentration　still　limits　the　performance　optimization.　Here,　we　employ　a　modulation　decoration　strategy　to　simultaneously　achieve　submicron-scale　constituents　and　compositional　modification　for　synergistic　optimization　of　thermoelectric　properties.　Amorphous　nano　Sb2S3　has　been　decorated　on　the　surface　of　Ag2Se　powders,　and　S　was　added　into　the　Ag2Se　matrix　through　an　ion　exchange　reaction　accompanied　by　the　formation　of　a　crystal/amorphous　mixed　secondary　phase　of　Sb2(S,　Se)3.　The　S　doping　reduced　the　excessive　intrinsic　carrier　concentration,　leading　to　modified　electrical　transport　properties　and　significantly　reduced　electrical　thermal　conductivity.　On　the　other　hand,　introducing　the　S　dopants　and　the　crystal/amorphous　interfaces　into　the　Ag2Se　matrix　could　increase　the　lattice　anharmonicity,　further　contributing　to　the　reduced　thermal　conductivity.　Consequently,　the　Ag2Se-0.4　%　Sb2S3　sample　obtains　a　high　average　zT　value　of　＞　1　in　the　temperature　range　of　300–390　K.　In　addition,　the　maximum　cooling　temperature　difference　of　over　85　K　can　be　predicted　in　an　Ag2Se/Ag2Se-0.4　%　Sb2S3　segregated　module　at　the　hot　side　temperature　of　350　K.　©　2025