Control and Characterization of Organic Solar Cell Morphology Through Variable-Pressure Solvent Vapour Annealing

Organic photovoltaics (OPVs) have recently experienced a tremendous increase in efficiency due to advancements in light absorbing materials and improvements in film morphology control. Solvent vapour annealing (SVA) of OPVs is an important post deposition method for controlling film morphology; however, current OPV SVA methods are difficult to reproduce, provide limited control over morphology, and lack scalability. In this thesis, it is shown that a flow through variable-pressure solvent vapour annealing (VP-SVA) system can be used to reproducibly and selectively anneal OPV active layers to controlled morphologies. VP-SVA is useful not only for the well-studied P3HT:PC61BM model system, but also for modern OPV active layers based on non-fullerene acceptors. Phase separation and material crystallinity are tuned by controlling the chloroform vapour concentration used in the annealing process; this was monitored by photo-induced force microscopy (PiFM) and grazing incidence wide angle X-ray scattering (GIWAXS), respectively. The results show that over-annealing can occur in both active layer blends, illustrating the importance of tuning the solvent vapour concentration