The damaging effects of the acidity in PEDOT:PSS on semiconductor device performance and solutions based on non-acidic alternatives

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS, has been widely used as an effective hole transporting material in many different organic semiconductor devices for well over a decade. However, despite having many strong features which make this material such a popular hole transport/injection layer, PEDOT:PSS is well-known to cause degradation in devices and limit their stability due to the acidity of the PSS chain. This review focusses on the attempts that have been made to combat this problem, with different strategies explored, including the development of neutral analogues, use of alternative materials and the introduction of barrier layers to prevent degradation of the electrode. Since solution-processing is a key advantage of using PEDOT:PSS, we concentrate on analogous materials that can also be solution-processed, with particular attention on whether orthogonal processing can be retained. We intend this work to be a useful guide for researchers considering enhanced device lifetimes, an important parameter when considering organic semiconductor devices for commercialisation.