Effect of Doping Concentration on Microstructure of Conjugated Polymers and Characteristics in N‐Type Polymer Field‐Effect Transistors |
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| Authors: | Chuan Liu Junhyuk Jang Yong Xu Hyo‐Jung Kim Dongyoon Khim Won‐Tae Park Yong‐Young Noh Jang‐Joo Kim |
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| Affiliation: | 1. State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat‐Sen University, Guangzhou, China;2. Department of Energy and Materials Engineering, Dongguk University, Jung‐gu, Seoul, Republic of Korea;3. Department of Materials Science and Engineering, Seoul National University, Gwanak‐gu, Seoul, Republic of Korea;4. Department of Organic Material Science and Engineering, Pusan National University, Geumjeoung‐gu, Busan, Republic of Korea |
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| Abstract: | Despite extensive progress in organic field‐effect transistors, there are still far fewer reliable, high‐mobility n‐type polymers than p‐type polymers. It is demonstrated that by using dopants at a critical doping molar ratio (MR), performance of n‐type polymer poly[[N,N9‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,59‐(2,29‐bithiophene)] (P(NDI2DO‐T2)) field‐effect transistors (FETs) can be significantly improved and simultaneously optimized in mobility, on–off ratio, crystallinity, injection, and reliability. In particular, when using the organic dopant bis(cyclopentadienyl)–cobalt(II) (cobaltocene, CoCp2) at a low concentration (0.05 wt%), the FET mobility is increased from 0.34 to 0.72 cm2 V–1 s–1, and the threshold voltage was decreased from 32.7 to 8.8 V. The relationship between the MR of dopants and electrical characteristics as well as the evolution in polymer crystallinity revealed by synchrotron X‐ray diffractions are systematically investigated. Deviating from previous discoveries, it is found that mobility increases first and then decreases drastically beyond a critical value of MR. Meanwhile, the intensity and width of the main peak of in‐plane X‐ray diffraction start to decrease at the same critical MR. Thus, the mobility decrease is correlated with the disturbed in‐plane crystallinity of the conjugated polymer, for both organic and inorganic dopants. The method provides a simple and efficient approach to employing dopants to optimize the electrical performance and microstructure of P(NDI2DO‐T2). |
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| Keywords: | doping mobility organic field‐effect transistors polymeric semiconductors stability |
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