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

doi:doi:10.1038/nmat2165

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 -electron system to -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 ( $approximately$ 3–6 $times$ 10^-
2 cm² V^-
1 s^-
1) and simultaneously excellent light-emission characteristics. These materials are expected to be of interest for light-emitting transistors³, light-emitting diode sources for optical communications⁴ 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 30 W cm^-
2 (0.1 nJ per pulse or 0.3 J cm^-
2) for 10 Hz, 12 ns, 390 nm excitation) and slope efficiencies (up to 11% ).

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