Sunlight stability of organic light-emitting diodes

This paper reports on the photodegradation of organic light-emitting diodes (OLEDs) due to exposure to visible and near-ultraviolet light. Such exposure affects strongly the device performance, e.g., the electroluminescence intensity and the device current decrease considerably, however, the photoluminescence remains unaffected. This photodegradation was investigated on various production-relevant classes of high-quality polymer semiconductors with different energy gaps, i.e., a yellowish-green polyphenylenevinylene derivative, a red polyfluorene derivative, and a blue polyspiro derivative. It will be demonstrated that the action spectrum of the photodegradation is strongly correlated with the fundamental absorption of the polymer itself. The indium-doped tin oxide (ITO) polymer interface was identified as the interface where photodegradation takes place, while the bulk of each layer (ITO or polymer) turned out to be insensitive to irradiation with visible or near-ultraviolet light. Furthermore, it is demonstrated that the photoinduced damage can be suppressed by inserting appropriate interlayer systems