The Air Stability and Operational Lifetime of Organic Photovoltaic Materials and Devices

Replacing energy intensive evaporated materials with solution processed alternatives is key to allowing OPVs to be fabricated using processes such as roll-to-roll (R2R) fabrication. However, roll-to-roll fabrication is primarily an ambient processing method, and as such the materials used need to be stable in the presence of oxygen and moisture. The effects of ambient oxygen and moisture on materials utilised in OPV devices are well documented, and in almost all cases are detrimental to device performance. Therefore, identifying materials and techniques that address these difficulties are essential.
In this thesis, using a combination of spectroscopic techniques and device characterisation, it is shown that applying optimised thermal treatments can reduce the uptake of moisture in molybdenum oxide hole transport layers, and reduce the resulting negative effects on device performance. The air stability, and therefore suitability for R2R fabrication, of several polymers are investigated. PFDT2BT-8 was identified as the most stable, and was utilised to fabricate OPV devices from solution in air using a variety of materials with efficiencies > 5%. In addition, the development of lifetime testing techniques, both in a laboratory and outdoor setting, evidencing operating lifetimes of > 7 years for devices utilising ambient solution processed materials.
In conclusion, this thesis describes the development of materials and techniques to allow for the fabrication of organic photovoltaic (OPV) devices from solution under ambient conditions, having high efficiencies and long operating lifetimes.