Controlling the Chain Orientation and Crystal Form of Poly(9,9-dioctylfluorene) Films for Low-Threshold Light-Pumped Lasers

Neat thin films of semiconducting polymers are attractive as efficient gain media toward optically pumped lasers. However, the optical loss and out-coupling of isotropic polymer thin films are far from being rationally regulated from the perspective of chain orientation and crystal form. Herein, we accomplished a simultaneous control of both chain orientation and crystal form in large-area highly ordered poly(9,9-dioctylfluorene) (PFO) thin films through epitaxial crystallization. The well-arranged PFO lamellae naturally shape a low-loss, graded-index waveguide to provide spatially distributed optical feedback. Moreover, much more horizontally oriented dipoles significantly enhance the light out-coupling efficiency. Thus, the only 65 nm-thickness oriented PFO films demonstrate excellent amplified spontaneous emission with a low excitation threshold (7.1 mu J/cm(2)) and a narrow full width at half-maximum (2.2 nm) measured in the perpendicular direction of PFO chains. This strategy opens an effective pathway to prepare high-performance polymer thin-film lasers and electrically pumped polymer lasers.

Automated summary

This study simultaneously controlled chain orientation and crystal form in large-area highly ordered PFO thin films through epitaxial crystallization, resulting in low-loss waveguides and enhanced light out-coupling efficiency, leading to excellent performance in amplified spontaneous emission.