Efficient single-crystal 4-N,N-dimethylamino-4-N-methyl-stilbazolium tosylate (DAST) on the optical, piezoelectric coefficient and structure of P(VDF-HFP) copolymer for energy conversion systems

Poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP) doped with 4-N,N-dimethylamino-4-N-methyl-stilbazolium tosylate (DAST) composites with various concentrations of DAST dye is prepared using the casting method. The crystal structure and optical properties of the pure and P(VDF-HFP)/DAST composites with various contents of DAST dye are investigated using various techniques such as UV–Vis spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and polarized optical microscopy (POM). The analysis of XRD data and FTIR spectra revealed that the β-fraction has been improved in the composite samples with increasing the content of DAST dye. Analysis of UV spectra displayed that the optical band gap of P(VDF-HFP) pure copolymer is 5.41 eV and has been reduced to be 3.75 eV for P(VDF-HFP)/10 wt% DAST that will be suitable for efficient systems of energy conversion and multijunction-based layer solar cells. Also, it is found that the nonlinear and linear optical parameters of the composite samples are DAST dye-dependent. Thermally stimulated depolarization current (TSDC) technique has been applied to investigate the dipolar and space charge relaxations of the composites. Moreover, it is observed that the pyroelectricity and piezoelectricity are enhanced with increasing the content of DAST dye. The highest content of the DAST dye showed maximum values of the pyroelectric and the piezoelectric coefficients of ~ 4 × 10–5 C/m2 K and ~ 34 pC/N at stress of 6.27 × 105 Pa, respectively. Our results of the polymer/dye composites give an opportunity of a promising material for flexible piezoelectricity devices used in many potential applications and energy harvesting systems.