Doping of organic semiconductors is crucial for the operation of organic (opto)electronic and electrochemical devices. Typically, this is achieved by adding heterogeneous dopant molecules to the polymer bulk, often resulting in poor stability and performance due to dopant sublimation or aggregation. In small-molecule donor–acceptor systems, charge transfer can yield high and stable electrical conductivities, an approach not yet explored in all-conjugated polymer systems. Here, we report ground-state electron transfer in all-polymer donor–acceptor heterojunctions. Combining low-ionization-energy polymers with high-electron-affinity counterparts yields conducting interfaces with resistivity values five to six orders of magnitude lower than the separate single-layer polymers. The large decrease in resistivity originates from two parallel quasi-two-dimensional electron and hole distributions reaching a concentration of ∼1013 cm–2. Furthermore, we transfer the concept to three-dimensional bulk heterojunctions, displaying exceptional thermal stability due to the absence of molecular dopants. Our findings hold promise for electro-active composites of potential use in, for example, thermoelectrics and wearable electronics.
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We thank C. Musumeci (Linköping University) for assistance with atomic force microscopy and S. Gustafsson (Chalmers) for assistance with TEM specimen preparation. This work was supported by the Knut and Alice Wallenberg foundation, VINNOVA (grant no. 2015-04859), the Swedish Research Council (grant agreement nos. 2016-03979, 2016-06146, 2016-05498, 2016-05990, 2018-03824), the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO Mat LiU no. 2009 00971), ÅForsk (18-313) and the European Research Council (ERC) under grant agreement no. 637624. We also thank the Chalmers Material Analysis Laboratory for their support of microscopes. T.P.R acknowledges funding from the Finnish Cultural Foundation and the Finnish Foundation for Technology Promotion. N.S. thanks the National Natural Science Foundation of China (grant no. 61805211). H.Y. acknowledges JST ALCA (JPMJAL1404) and the Futaba Foundation. Work at the University of Washington was supported by the National Science Foundation (DMR-1708450). D.F. acknowledges the Deutsche Forschungsgemeinschaft (DFG) for the grant ‘Molecular Understanding of Thermo-Electric Properties in Organic Polymers (FA 1502/1-1)’, and the Regional Computing Centre (RRZK) of Universität zu Köln, for providing computing time and resources on the HPC CHEOPS.
The authors declare no competing interests.
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Xu, K., Sun, H., Ruoko, TP. et al. Ground-state electron transfer in all-polymer donor–acceptor heterojunctions. Nat. Mater. 19, 738–744 (2020). https://doi.org/10.1038/s41563-020-0618-7
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