3.2. UV–Vis spectroscopy
Fig. 1 shows the UV–Vis absorption spectra of P3HTs. The
observed max of P3HT-96, P3HT-70 and P3HT-58 are 555, 491 and 435 nm, respectively. The decreasing max implies the reduction of regioregularity which results from poor -stacking and high chain folding [4]. Apart from max, P3HT-96 shows two shoulders at 523 and 603 nm, indicating the vibronic coupling of polymeric chains [19]. For P3HT-70, two weak shoulders at 535 and 584 nm are also observed where as for P3HT-58 no such additional shoulders are observed. This indicates that extend of chain packing in P3HT-58 is poorer as compared to P3HT-70 and P3HT-96. The reason for better chain packing in P3HT-96 and P3HT-70 is attributed to the method of polymerization. The band gaps of the polymers calculated from the onset of absorption spectra for P3HT-96, P3HT-70 and P3HT-58 are found to be 1.85, 1.90 and 2.08 eV, respectively. As the band gap of the conjugated polymers depends upon the effective conjugation length, the increasing trend indicates reduction of the conjugation which is due to the decrease in effective stacking and increase in chain folding of the polymers.
3.2. UV–Vis spectroscopy Fig. 1 shows the UV–Vis absorption spectra of P3HTs. Theobserved max of P3HT-96, P3HT-70 and P3HT-58 are 555, 491 and 435 nm, respectively. The decreasing max implies the reduction of regioregularity which results from poor -stacking and high chain folding [4]. Apart from max, P3HT-96 shows two shoulders at 523 and 603 nm, indicating the vibronic coupling of polymeric chains [19]. For P3HT-70, two weak shoulders at 535 and 584 nm are also observed where as for P3HT-58 no such additional shoulders are observed. This indicates that extend of chain packing in P3HT-58 is poorer as compared to P3HT-70 and P3HT-96. The reason for better chain packing in P3HT-96 and P3HT-70 is attributed to the method of polymerization. The band gaps of the polymers calculated from the onset of absorption spectra for P3HT-96, P3HT-70 and P3HT-58 are found to be 1.85, 1.90 and 2.08 eV, respectively. As the band gap of the conjugated polymers depends upon the effective conjugation length, the increasing trend indicates reduction of the conjugation which is due to the decrease in effective stacking and increase in chain folding of the polymers.
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