Raman Scattering Methods for Monitoring the Electric Properties of the Postannealed Bulk Heterojunction

In the case of bulk heterojunctions (BHJs) of regioregular poly(3-hexylthiophene) (P3HT) and the soluble fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), electrical properties have been studied based on the Raman spectroscopy. Significantly, a well enough noteworthy phenomenon is the ″return-back″ shift of the Raman signal at the ∼1450 cm–1 with increasing annealing temperature, which was first observed using the normal Raman spectroscopy of the BHJ system. Based on the Herzberg–Teller coupling term in the organic–organic system, the ″return-back″ shift may be due to the charge transfer (CT), resulting in the significant change of resistivity (ρ). More importantly, the low annealing temperature-dependent frequency shift (ν) is carefully investigated with ρ, and ρ ∝ (−ν)2. In addition, the connection between Raman intensity and ρ is also established. This study is unprecedented to establish a clear connection between frequency shift and electrical properties, indicating that the Raman technique opens an avenue to analyze the electrical properties and characterize the performance of the battery.