Enhancement of light-emitting properties by simultaneously patterning and controlling molecular alignment in polyfluorene thin films

Abstract

Soft nano-imprinting lithography is used to fabricate PFO nanogratings. On the one hand, soft nano-imprinting lithography has been well explored to create nanostructures and induce molecular orientation in conjugated polymer thin films because of its limited cost, high throughput, and small feature size. On the other hand, the pure α-conformation PFO nanogratings with highly ordered molecular chains can be achieved with graphoepitaxial alignment without any molecular chain degradation. Hence, herein, we demonstrated that large-area PFO (poly(9,9-dioctylfluorene)) nanogratings could be fabricated by this effective way with high accuracy of patterning and chain alignment controllability. The molecular chain alignment degree can be tuned due to entropic and geometrical reasons; this has been verified by polarized absorption and GIWAXD (grazing incidence wide angle X-ray diffraction). Moreover, both the optical and electrical pumping properties have been characterized. In addition, not only optimized polarizability was observed at the most oriented situation, but also 20% more light was extracted from this PLED device.