Abstract
Efficient conjugated polymer optoelectronic devices benefit from concomitantly high luminescence and high charge carrier mobility. This is difficult to achieve, as interchain interactions, which are needed to ensure efficient charge transport, tend also to reduce radiative recombination and lead to solid-state quenching effects. Many studies detail strategies for reducing these interactions to increase luminescence, or modifying chain packing motifs to improve percolation charge transport; however achieving these properties together has proved elusive. Here, we show that properly designed amorphous donor-alt-acceptor conjugated polymers can circumvent this problem; combining a tuneable energy gap, fast radiative recombination rates and luminescence quantum efficiencies >15% with high carrier mobilities exceeding 2.4 cm2/Vs. We use photoluminescence from exciton states pinned to close-crossing points to study the interplay between mobility and luminescence. These materials show promise towards realising advanced optoelectronic devices based on conjugated polymers, including electrically-driven polymer lasers.
Highlights
Efficient conjugated polymer optoelectronic devices benefit from concomitantly high luminescence and high charge carrier mobility
Φ generally increases with energy gap (Eg), and this trend is shown for various polymers in Fig. 1a, and tabulated values are provided in Supplementary Table 1
In the present work, we have demonstrated a class of conjugated polymers with low degree of energetic disorder, that exhibit simultaneously a high carrier mobility >2 cm2/Vs and a high photoluminescence quantum efficiency >15% and, to the best of our knowledge, the highest Φ · μ values reported far for conjugated polymers, which outcompete the state-of-the-art by >10×
Summary
Efficient conjugated polymer optoelectronic devices benefit from concomitantly high luminescence and high charge carrier mobility This is difficult to achieve, as interchain interactions, which are needed to ensure efficient charge transport, tend to reduce radiative recombination and lead to solid-state quenching effects. We show that properly designed amorphous donor-alt-acceptor conjugated polymers can circumvent this problem; combining a tuneable energy gap, fast radiative recombination rates and luminescence quantum efficiencies >15% with high carrier mobilities exceeding 2.4 cm2/Vs. We use photoluminescence from exciton states pinned to close-crossing points to study the interplay between mobility and luminescence. We use photoluminescence from exciton states pinned to close-crossing points to study the interplay between mobility and luminescence These materials show promise towards realising advanced optoelectronic devices based on conjugated polymers, including electrically-driven polymer lasers. This has been attributed to a number of different mechanisms, including increased exciton diffusion to pre-existing chemical defects or exciton quenching ‘trap’ sites[12,13], an additional density of charge-transfer interchain states with low oscillator strength[13,14,15,16], additional fast non-radiative recombination channels arising from intersecting bands[17,18,19], and the suppression of radiative recombination pathways by H-aggregate formation[20]
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