| Summary: | Semiconductor composite materials have attracted interest from surface-enhanced Raman scattering (SERS) substrate research. Here, we investigate an organic-inorganic semiconductor heterojunction P3HT@Ag<sub>2</sub>NCN composite film as a recyclable SERS substrate for molecule detection application. Our study shows that the SERS substrate of the composite P3HT@Ag2NCN composite film has high sensitivity, excellent signal reproducibility, and is reusable. Significant π-stacking of the probe molecules with the thiophene π-cores molecules from P3HT plays an important role in the large SERS enhancement by the charge transfer mechanism. Due to physical interaction between P3HT and Ag<sub>2</sub>NCN, the organic-inorganic semiconductor heterojunction structure further improves charge transfer efficiency and the SERS property. Our results show that the enhancement factor (EF) of P3HT@Ag<sub>2</sub>NCN composite films (EF = 6147 ± 300) for the probe molecule methylene blue is more than 7 times that of P3HT substrate (EF = 848 ± 85) and is about 75 times that of Ag<sub>2</sub>NCN nanorods (EF = 82 ± 8). In addition, the SERS substrates of the P3HT@Ag<sub>2</sub>NCN composite film also display excellent reusability and signal reproducibility (<i>RSD</i> < 4.8%). Our study opens up a new opportunity for designing an ideal SERS substrate with high sensitivity, selectivity, long-term stability, low cost, and reusability.
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