Improved efficiency organic photovoltaic cells through morphology control and process modification

Organic photovoltaic (OPV) cells have drawn great attention due to the potential to produce flexible, light weight, affordable solar cells using polymer organic photovoltaic materials; however, the current power conversion efficiency achieved for these systems is too low for widespread implementation of the technology. Morphology and phase separation are key factors determining the performance of organic photovoltaic cells. Precise control of the size and distribution of the phase-separated photoactive domains is necessary for optimum photon-electron conversion. Polyhedral oligomeric silsesquioxane (POSS) nanostructured chemicals have the potential to provide enhanced control of morphology, crystallinity, and phase dispersion in polymeric blend systems. In this work, POSS molecules with different organic functionalities were utilized to control OPV film morphology. The light absorption, crystallinity, and phase separated domain size were evaluated to determine the relationship between POSS structures and film characteristics. The selected POSS molecules were utilized for further device fabrication and performance measurements, with which the POSS enhanced performance was revealed. Furthermore, processing conditions are also important in determining the performance and phase separated morphology of the OPV devices. The effects of solvent vapor annealing and thermal annealing were evaluated in terms of light absorption, crystallinity, long-term stabilitiy, and device performance.