Center for Functional Nanomaterials Seminar

Organic photovoltaics (OPV) have been considered as a potential low-cost solar energy conversion solution for a clean, safe, affordable and sustainable energy future. They have attracted tremendous academic and industrial interests in recent years, which stems from the deposition flexibility of lightweight organic thin films on a variety of very-low-cost substrates such as glass, plastic or metal foils. Currently, there are three main ongoing avenues to improve the power conversion efficiency of OPVs: the development of new organic materials, improved process control and novel device architecture design. Through molecular design with chemical modification of functional organic molecules, a family of new highly absorptive squaraine (SQ) materials has been systematically synthesized and explored to improve the sunlight harvesting and charge transport. The spin-cast SQ donors are then coated with fullerene acceptors to form a unique nanocrystalline OPV device. This combination of a novel and efficient family of SQ donors, a unique device architecture and optimized fabrication processes leads to high efficiency solar cells. For example, solar cells with efficiencies of ~6.0 % and a fill factor ~0.74 are achieved, which to our knowledge both are the highest numbers reported to date for small molecule OPVs. These results suggest that SQs have promise for achieving further increases in solar cell efficiency in a more ordered nanocrystalline OPV, as will provide an ideal material system and device architecture for low-cost large-area OPVs using roll-to-roll printing techniques.