19 Device stability in organic optoelectronics

After efficiency, lifetime is the second-most-important parameter for organic devices. This chapter highlights the state of the art with regard to device stability in organic light-emitting diodes and organic photovoltaics, with discussion of the critical role that interfaces play in their performance. The chapter begins with a brief overview of degradation, including definitions and measurement approaches. It then proceeds to examine major mechanisms of device breakdown. First, the role of interfacial adhesion is highlighted, as operational and environmental delamination is a critical issue, particularly for flexible devices. Morphological stability is described next, examining dewetting, crystallization, and phase segregation as major problems for high-efficiency devices. This is followed by a section on intrinsic chemical instability at the electrodes and one on water- and oxygen-induced degradation, which remains the most critical challenge in device stability. Combating these mechanisms has been the focus of research into encapsulants and buffer layers, and also has led to the introduction of inverted devices as a successful new device architecture. A description of two final mechanisms, charge carrier-induced degradation and photoinduced degradation, are also covered briefly. The chapter ends with a historical look at how lifetimes have evolved, highlighting the current goals for next-generation, stable organic devices.