Simultaneous optimization of charge-carrier mobility and optical gain in semiconducting polymer films

The combination of efficient light emission and high charge-carrier mobility has thus far proved elusive for polymer semiconductors, with high mobility typically achieved by cofacial pi-electron system to pi-electron system interactions that quench exciton luminescence(1,2). We report a new strategy, comprising the introduction of a limited number of more effective hopping sites between otherwise relatively isolated, and thus highly luminescent, polyfluorene chains. Our approach results in polymer films with large mobility (mu approximate to 3-6 x 10(-2) cm(2) V-1 s(-1)) and simultaneously excellent light-emission characteristics. These materials are expected to be of interest for light-emitting transistors(3), light-emitting diode sources for optical communications(4) and may offer renewed hope for electrically pumped laser action(2,5,6). In the last context, optically pumped distributed feedback lasers comprising one-dimensional etched silica grating structures coated with polymer have state-of-the-art excitation thresholds (as low as 30Wcm(-2) (0.1 nJ per pulse or 0.3 mu J cm(-2)) for 10 Hz, 12 ns, 390nm excitation) and slope efficiencies (up to 11%).