Carbon  nanotubes  and  their  composite  thermoelectric  (TE)  materials  have  significant  advantages  in supplying power to flexible electronics due to their high electrical conductivity, excellent flexibility, and facile preparation technology. In this work, stable n-type silver ammonia-polyethyleneimine/single-walled carbon nanotube ([Ag(NH₃)₂]⁺-PEI/SWCNT) composite films were facilely prepared by solution blending and  vacuum-filtration  methods.  The  results  demonstrate  that  light  silver  ammonia  doping  optimizes the carrier concentration and carrier mobility of the composite film, and a maximum power factor (PF) of [Ag(NH₃)₂]⁺-PEI/SWCNT  of  91.9  μW m^-1 K^-2  was  obtained,  which  is  higher  than  that  of  PEI/SWCNT (70.0 μW m^-1 K^-2). Furthermore, when the composite films were reduced by the NaBH4  solution, the Seebeck coe?cient and the PF value were further increased to -45.5 μV K^-1  and 115.8 μW m^-1 K^-2, respectively. For demonstration, a maximum output voltage of 13.8 mV and output power of 492 nW were achieved using a three p–n junction-based TE device constructed by [Ag(NH₃)₂]⁺-PEI/SWCNT at a temperature difference of 50 K. Thus, this study provides a metal complex ion doping strategy to improve thermoelectrical  properties  and  air  stability  of  the  PEI/SWCNT  composite  films,  which  have  potential applications in flexible electronics.