Enhanced Charge Transport in a Conjugated Polymer Blended with an Insulating Polymer

• Published in: Chemistry, an Asian journal an Asian journal, 2020-03, Vol.15 (6), p.796-801
• Main Authors: Kim, Hyung Do, Iriguchi, Ryo, Fukuhara, Tomohiro, Benten, Hiroaki, Ohkita, Hideo
• Format: Article
• Language: English
• Subjects: Atomic force microscopes; Atomic force microscopy; Blend Film; Carrier density; Carrier Mobility; Charge density; Charge Transport; Chemistry; Conductivity; Conjugated Polymer; Current carriers; Dilution; Excimers; Hole conductivity; Insulating Polymer; Local current; Mixtures; Polymers; Polystyrene resins; Quinoxalines; Temperature dependence; Weight
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201901743

Herein, the hole transport in a quinoxaline–thiophene based conjugated polymer (PTQ1) mixed with an insulating polystyrene (PS) was studied by macroscopic and local current density−voltage characteristics measurements. As a result, we found that the hole conductivity in PTQ1 : PS blends increases as the weight ratio of PTQ1 is reduced down to 20 wt%. This is mainly ascribed to increases in mobility because the charge carrier density would be constant in the insulating PS matrix. With decreasing PTQ1 weight ratio in the blends, the absorption bandwidth of PTQ1 and additional emission due to excimer decreased, suggesting that interchain interactions are suppressed. By measuring the temperature‐dependent conductivity, we also found that the activation energy for the hole conductivity is smaller in PTQ1 : PS blends than in PTQ1 neat films. These findings suggest that trap sites decrease because of the suppressed interaction between PTQ1 chains in blend films. We also measured conductive atomic force microscope images of the blend films to clarify the local conductive property. For PTQ1 neat films, a low conductive image was observed over the entire film. For PTQ1 : PS blends, on the other hand, many highly conductive spots were locally found. We thus conclude that the dilution of PTQ1 chains in the PS matrix leads to a lower formation of trap sites, resulting in more conductive transport in PTQ1 : PS blends than in PTQ1 neat films. The hole transport in a quinoxaline–thiophene based conjugated polymer (PTQ1) mixed with insulating polystyrene (PS) has been studied by analyzing macroscopic and microscopic current density–voltage characteristics. As a result, not only the hole conductivity but also the local current image was higher in PTQ1 : PS blends with 20 wt% of PTQ1 than in PTQ1 neat films. This is due to the lower formation of trap sites by dilution of PTQ1.