Display omitted •Facilely realizing the boost of interfacial carrier transports.•Effectively coating Bi0.5Sb1.5Te3 fillers with highly conductive CuTe layer.•Achieving highly crystallized PEDOT:PSS as the matrix.•Producing promising σ of ~2300 S cm−1 and peak S2σ of 312 µW m−1 K−2 at room temperature.•Generating promising open-circuit thermovoltage of ~7.7 mV with human wrist as the thermal source. Incorporating inorganic thermoelectric fillers into conductive polymers is one promising strategy to develop high-performance flexible thermoelectric films. However, due to the relatively high interfacial contact resistance between fillers and polymers, carriers tend to be scattered at the interfaces during the interfacial transports, which deteriorates the electrical properties of the system, and in turn leads to low energy conversion efficiency. Here, a new strategy is developed to optimize interfacial carrier transports in Bi0.5Sb1.5Te3/PEDOT:PSS composite, by coating Bi0.5Sb1.5Te3 fillers with highly conductive CuTe layer. With highly crystallized PEDOT:PSS prepared as the matrix, high-performance Cu-Bi0.5Sb1.5Te3 /PEDOT:PSS film is fabricated with promising σ of ~2300 S cm−1 and peak S2σ of 312 µW m−1 K−2 at room temperature, which reaches to a record-high value in the reported Bi0.5Sb1.5Te3/PEDOT:PSS composites. Accordingly, a home-made flexible thermoelectric device is fabricated using our prepared composites, generating a promising open-circuit thermovoltage of ~7.7 mV with the human wrist as the thermal source. This study addresses the significance of interfacial carrier transport, hinting the bright prospects of cheap conductive polymers as the effective power source of wearable electronics.