Tuning the Seebeck coefficient of naphthalenediimide by electrochemical gating and doping.
Tuning the Seebeck coefficient of naphthalenediimide by electrochemical gating and doping.
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DOI：
10.1039/c7nr00571g
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发表时间：
2017-04
期刊：
影响因子：
6.7
通讯作者：
Q. Al-Galiby;H. Sadeghi;D. Manrique;C. Lambert
中科院分区：
文献类型：
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作者：
Q. Al-Galiby;H. Sadeghi;D. Manrique;C. Lambert
我们研究了电化学门控和掺杂对萘二酰亚胺（NDI）单分子塞贝克系数的影响。该分子由一个NDI核和两个在海湾区域位置的烷基链组成，通过苯并噻吩（DBT）锚基团连接到金电极。通过在中性、自由基和双阴离子电荷状态之间切换，我们能够相对于电极的费米能来调节分子能级。三种电荷态的单分子室温Seebeck系数分别为-294.5 μV K-1，122 μV K-1，144 μV K-1，室温功率因数分别为4.4 × 10-5 W m-1 K-2，3 × 10-5 W m-1 K-2，8.2 × 10-4 W m-1 K-2.作为优化热电性能的进一步策略，我们还研究了用电子给体（TTF）或电子受体（TCNE）掺杂NDI对声子和电子传输的影响。结果表明，TTF掺杂使室温下的Seebeck系数和功率因数从裸NDI的-73.7 μV K-1和2.6 × 10-7 W m-1 K-2提高到TTF掺杂时的-105 μV K-1和3.6 × 10-4 W m-1 K-2。NDI-TTF的低热导率与较高的塞贝克系数和较高的电导率相结合，导致ZT = 1.2的最大热电优值，这比裸NDI高几个数量级。这表明NDI Seebeck系数的符号和大小都可以通过电化学门控和掺杂可逆地调节，表明这种氧化还原活性分子是用于超薄膜热电器件的有吸引力的材料。
We investigate the sign and magnitude of the single-molecule Seebeck coefficient of naphthalenediimide (NDI) under the influence of electrochemical gating and doping. The molecule consists of a NDI core with two alkyl chains in the bay-area position, connected to gold electrodes via benzothiophene (DBT) anchor groups. By switching between the neutral, radical and di-anion charge states, we are able to tune the molecular energy levels relative to the Fermi energy of the electrodes. The resulting single-molecule room-temperature Seebeck coefficents of the three charge states are -294.5 μV K-1, 122 μV K-1 and 144 μV K-1 respectively and the room-temperature power factors are 4.4 × 10-5 W m-1 K-2, 3 × 10-5 W m-1 K-2 and 8.2 × 10-4 W m-1 K-2. As a further strategy for optimising thermoelectric properties, we also investigate the effect on both phonon and electron transport of doping the NDI with either an electron donor (TTF) or an electron acceptor (TCNE). We find that doping by TTF increases the room-temperature Seebeck coefficient and power factor from -73.7 μV K-1 and 2.6 × 10-7 W m-1 K-2 for bare NDI to -105 μV K-1 and 3.6 × 10-4 W m-1 K-2 in presence of TTF. The low thermal conductance of NDI-TTF, combined with the higher Seebeck coefficient and higher electrical conductance lead to a maximum thermoelectric figure of merit of ZT = 1.2, which is higher than that of bare NDI in several orders of magnitude. This demonstrates that both the sign and magnitude of NDI Seebeck coefficient can be tuned reversibly by electrochemical gating and doping, suggesting that such redox active molecules are attractive materials for ultra-thin-film thermoelectric devices.