Stability and degradation of organic photovoltaics

Organic photovoltaics (OPV)s are a type of renewable energy technology that have gained a large amount of interest in the scientific literature in recent years,motivated by their potential for large scale use as a flexible, semi-transparent and low cost renewable energy alternative. Due to their flexible and semi-transparent nature, there are several potential applications that are not available to conventional photovoltaics, such as use in windows or wearables. However, several key issues remain to be addressed before large scale, cost effective use is possible. Arguably the foremost issue is the lifetime of the devices; which is currently too short for practical use. There are various degradation processes that can occur in these devices and often numerous such processes occur simultaneously. To improve device stability, their degradation must be investigated and understood. The most common method for investigating degradation of OPVs is lifetime measurements. Thus, this thesis presents details of the construction of an automated degradation system for performing lifetime measurements on small (5mm²) OPV devices. Using this degradation system, systematic studies on the stability of several OPV architectures under various lighting conditions were conducted. Devices were constructed with a range of material systems, to elucidate degradation behaviour related to materials and interfaces. The stability of OPV devices was shown to be dependent on material and interface stability,as well as illumination conditions. Observed trends changed significantly when different lighting conditions were employed. Furthermore, the degradation behaviour of printed OPVs was found to be dependent on the thickness of buffer layers used, with unexpected trends observed in the degradation for different thicknesses. Through rigorous degradation measurements presented in this thesis, a more extensive picture of the stability and degradation of OPV devices has been obtained. This understanding provides several pathways for fabrication of more stable OPV devices, including avoiding materials observed to cause rapid degradation, and using filters on appropriate structures to reduce photo-active degradation.