This study introduces a flexible and scalable charge-trapping intermediate layer of conjugated polymeric film comprising [PANI/PEDOT:PSS]n between the [PVA/PDDA]n triboelectric layer and graphene-based [PVA/GNP-PSS]n electrode using the layer-by-layer (LbL) assembly method. By varying the deposition layers, the optimal coating layout was identified as 2 and 8 bilayers of intermediate and triboelectric layers, respectively. The triboelectric nanogenerator (TENG) fabricated with this optimal configuration achieved peak output voltage and current of 180 V and 9 μA, respectively, at 3 Hz and 5 N against PDMS. This represents a 63.6% increase in output voltage and a 20% increase in output current compared to the TENG without the intermediate charge-trapping layer, owing to the surface charge density reaching 61.5 μC/m2. Furthermore, an ultrathin, free-standing PANI–PEDOT:PSS film was encapsulated in a free-standing PVA–PDDA film, which resulted in a significant TENG output performance of 315 V. Inspired by these TENG results, we investigated the flame-retardant properties of the LbL [PANI/PEDOT:PSS]n coating on polyurethane foam (PUF) and demonstrated, through the open flame test, that the presence of the flame-retardant coating prevented flame flashover, melting, and dripping of the burning PUF. The coated PUF exhibited a lower heat release capacity of 402 J/g·K compared to neat PUF, and the thermal degradation of coated PUF resulted in the formation of 10.95 wt % residue in the TGA test. In addition, the TENG fabricated using the coated foam achieved a significant output performance. Therefore, this study contributes to future flame-retardant energy harvesting materials via sustainable LbL assembly.