Concentration-Dependent Sers of P3ht in Ag/P3ht/Mba System: Charge-Transfer Study

Abstract

A sandwich structure of metal/organic semiconductor/probe molecules was constructed by using a layered self-assembly method. By varying the concentration of the poly(3-hexylthiophene) (P3HT) solution to control the thickness of the P3HT thin film, the dielectric environment surrounding the Ag nanoparticles can be altered and the localized surface plasmon resonance (LSPR) phenomenon can be effectively regulated. Using mercaptobenzoic acid (MBA) as a probe molecule, the surface-enhanced Raman scattering (SERS) enhancement performance of the Ag/P3HT composite system was studied. Our results indicated that when the P3HT concentration was 10-5 g/mL, the enhancement of the SERS intensity tends to be stable, and ρCT reaches the maximum value. Our findings also suggest that the SPR effect at the Ag/P3HT interface promotes the transfer of electrons from the conduction band (CB) of Ag/P3HT to the lowest unoccupied molecular orbital (LUMO) of MBA, resulting in a significant enhancement of the SERS intensity. With a detection limit of MBA molecules as low as 10-10 mol/L, our study affirmed the excellent sensitivity and efficiency of the Ag/P3HT composite as a SERS substrate. This study will help broaden the research scopes of SERS substrates and contribute to the exploration of the SERS mechanism.

Keywords: SERS, P3HT, MBA, Charge-transfer