Polymer Morphology and Device Performance in Polymer Electronics

Abstract

Since the first successful fabrication of the polymer light-emitting diode (PLED) using poly(p-phenylenevinylene) (PPV) as the active material,¹ there has been widespread research interest in conjugated polymers. The lightweight, flexibility, ease of processing, and the unique electrical and photonic semiconducting properties are among the most attractive characteristics of this class of materials. Because some of these materials can be obtained in solution form, spin-coating has become the most commonly used technique for obtaining uniform thin films of these materials. It is often noted that results published by different groups are inconsistent. For example, as shown in Fig. 6.1, emission spectra of poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) thin films can be dramatically different. In addition, fluorescence decay dynamics of MEH-PPV films with a photoluminescence (PL) spectrum similar to curve a in Fig. 6.1 reported by Jakubiak Rothberg² are significantly different from that with a PL spectrum similar to curve b in Fig. 6.1 reported by Samuel et al.³ The dispute of the charge carriers’ mobility is another example. Scott et al.,^4,5 found that the electron is highly mobile in MEH-PPV films. Blom et al.⁶ suggested that the charge recombination zone is next to the cathode, which suggests that the holes move faster than the electrons. It was also noted that hole transport is dispersive and, therefore, an interpretation in terms of charge carrier mobility is not meaningful.⁷