ION MODULATED ORGANIC TRANSISTORS - Doria

Nikolai Kaihovirta3. RESULTS AND DISCUSSIONSThe PTFE:PFSA-based MemFET is used as the model device (Figure3.18). The sterically hindered phenolic antioxidant 4,4´-methylenebis(2,6-di-tert-butyl phenol) (subsequently denoted as stabilizer) is added intothe P3HT-solution. The chemical structure for the stabilizer is shown inFigure 3.18 (b) and the stabilization mechanism is illustrated in Scheme3.2. Accordingly, the stabilizer structure serves several purposes [80].Highly reactive alkoxy and peroxy radicals are stabilized by the easilyabstractable hydrogen from the phenolic moiety. Furthermore, theantioxidant complex is stabilized by the resonance structure, provided bythe aromatic system. The alkyl substituents at 2,6-positions provide twofunctionalities. Firstly, they enhance the hydrogen donating ability of theantioxidant. Secondly, they hinder the formed phenoxyl radical to furtherreact by abstracting hydrogen from the polymeric backbone.COOHROOOCO+ROOHOScheme 3.2. The stabilization mechanism for sterically hindered phenolicantioxidants.P3HT- and P3HT+stabilizer-samples were fabricated by spin-coatingthe solutions on respective glass substrates. Thermal stress studies werecarried out in ambient air and in darkness at 110 ºC. The change in theUV-Vis absorption was regularly monitored on the samples in order toobserve any signs for improved lifetime in the stabilized P3HT. Theresults are depicted in Figure 3.19. The change in absorbance is similar inboth cases. Initially, the annealing of the samples will improve theabsorption but after a few hours of annealing both samples displaybleaching of the absorbance peak. Further thermal stress will result inblue-shift of the peak and eventually to a complete loss of the absorbance[81]. Even though the bleaching seemingly falls with equal rates, afterfour hours of annealing, the absorbance is consistently higher throughoutC42