Influence of spin–spin exchange on charge transfer in PANI-ES/P3DDT/PCBM composite

• Organic PANI-ES/P3DDT/PCBM composites were formed on ceramic plates.
• The spin and electronic properties of charge carriers were studied before and upon white light illumination.
• Magnetic resonance parameters show strong exchange spin–spin interaction.
• We report a spin-assisted charge transfer in the PANI-pTSA/P3DDT/PCBM composite.

The first results of the light-induced EPR study of magnetic, relaxation and dynamic parameters of charge carriers stabilized in emeraldine salt form of polyaniline (PANI-ES) highly doped with sulfuric (SA) and para-toluenesulfonic (pTSA) acids, spin pairs background photoinitiated in bulk heterojunctions formed by poly(3-dodecylthiophene) with [6,6]-phenyl-C61-butyric acid methyl ester (P3DDT/PCBM) as well as charge carriers in appropriate PANI-ES/P3DDT/PCBM composites are described. Main magnetic resonance parameters for positively charged polarons in both polymer backbones and negatively charged methanofullerene ion-radical in the P3DDT/PCBM bulk heterojunctions were determined separately from deconvoluted LEPR spectra. These parameters were shown to be governed by the conformation of the PANI-ES chains which determines insulating and conducting forms of the PANI-SA and PANI-pTSA samples, respectively. The effective absorption peak-to-peak line width was described in terms of the exchange interaction of the polarons hopping along the neighboring solitary PANI and P3DDT nanoparticles. Paramagnetic susceptibility of such charge carriers was interpreted in the framework of the model of exchange coupled spin pairs differently distributed in parental polymer matrices. Exchange interaction increases dramatically as the PANI-SA network is replaced by the PANI-pTSA one in the triple composite. This deepens overlapping of wave functions of polarons in both polymer matrices and leads to the increase in the energy barrier which they overcome crossing a bulk heterojunctions and acceleration of spin–lattice relaxation in PANI-pTSA. Polaron diffusion in P3DDT was shown to govern spin susceptibility of methanofullerene anion radicals rotating between its chains.

Figure optionsDownload as PowerPoint slide