Chain Coupling and Luminescence in High-Mobility, Low Disorder Conjugated Polymers.

Optoelectronic devices based on conjugated polymers often rely on multilayer device architectures, as it is diffcult to design all the different functional requirements, in particular the need for efficient luminescence and fast carrier transport, into a single polymer. Here we study the photophysics of a recently discovered class of conjugated polymers with high charge carrier mobility and low degree of energetic disorder and investigate whether it is possible in this system to achieve by molecular design a high photoluminescence quantum yield without sacrificing carrier mobility. Tracing exciton dynamics over femtosecond to microsecond timescales, we show that nearly all non-radiative exciton recombination arises from interactions between chromophores on different chains. We evaluate the temperature dependence and role of electron-phonon coupling leading to fast internal conversion in systems with strong inter-chain coupling, and the extent to which this can be turned off by varying side chain substitution. By sterically decreasing inter-chain interaction, we present an effective approach to increase the fluorescence quantum yield of low energy gap polymers. We present a red-NIR-emitting amorphous polymer with the highest reported lm luminescence quantum efficiency of 18 % whose mobility concur- rently exceeds that of amorphous-Si. This is a key result towards the development of single-layer optoelectronic devices which require both properties.

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