Cation-exchange doping of n-type conjugated polymers entailing glycolated side chains

Improving the doping efficiency of n-type conjugated polymers is a significant challenge in the field. However, the limited availability of dopants and methods for doping results in the electrical performance of n-type materials lagging behind that of p-type materials. In this study, we introduce a novel method for n-doping called cation-exchange doping, which enhances the doping levels of n-type polymers that incorporate glycolated side chains. We selected two n-type conjugated polymers to undergo cation-exchange doping using the direct dopant tetrakis(dimethylamino)ethylene (TDAE), along with three cations: Li+, 1-Ethyl-3-methylimidazolium (EMIM+), and tributylmethylphosphonium (TBMP+). All of these doped materials demonstrate improved thermoelectric performance and achieve deeper doping levels compared to doping with TDAE alone. The two polymers exhibit distinct electrical properties and thermoelectric performance related to cations, highlighting the importance of counterion engineering in optimizing the outcomes of cation-exchange doping. This can be explained by the cation-mediated density of states and electrical conductivity resulting from electrochemical doping. This research demonstrates a universal method for cation-exchange doping in n-type polymer semiconductors and offers new insights into understanding the interaction between polymers and counterions in organic electronics.
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Part 1 outlines the experimental protocols and chemical reagents employed in the cation-exchange doping process. The data in Part 2 confirm successful cation exchange, as evidenced by increased Raman peak intensity ratios (P-3O: I₁₃₀₅/I₁₃₂₅; f-BTI2g-SVSCN: I₁₃₈₀/I₁₄₁₀), attenuated optical absorption spectra, reduced TDAE-specific FT-IR signals, and characteristic phosphorus (P) signatures in XPS analysis. Part 3 demonstrates superior electrical properties and thermoelectric performance in cation-exchanged systems compared to TDAE-doped counterparts, attributed to enhanced carrier concentration and reduced energetic barriers for charge transport. Part 4 reveals cation-specific variations in surface morphology and crystalline structure, though no significant correlation between electronic properties and microstructural ordering is observed. In Part 5, we propose a mechanistic framework linking cation-specific characteristics to performance enhancements. Part 6 provides supplementary data characterizing the performance of TDAE-doped polymers and reveals electronic stability enhancement via cation-exchange modification.
Funded by National Natural Science Foundation of China (Nos. 52273201, 52473199, 62205143), Jilin Scientific and Technological Development Program (No. 20230402070GH, 20240101172JC) and a grant for Distinguished Young Scholars of the National Natural Science Foundation of China (Overseas), and China Postdoctoral Science Foundation Funded Project (No. grant 2022M723077)