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Band Engineering and Majority Carrier Switching in Isostructural Donor-Acceptor Complexes DPTTA-F TCNQ Crystals (X =
Yingying Liang1,2, Yunke Qin1,2, Jie Chen1,2
1Beijing National Laboratory for Molecular Sciences Key Laboratory of Organic Solids Institute of Chemistry Chinese Academy of Sciences Beijing 100190 China.
Abstract:
Three isostructural donor-acceptor complexes DPTTA-F TCNQ (X = 1, 2, 4) are investigated experimentally and theoretically. By tuning the number of F atoms in the acceptor molecules, the resulting complexes display a continuous down shift of the valence band maximum, conducting band minimum, and optical bandgap. The majority carriers convert from hole (DPTTA-F1TCNQ), balanced hole, and electron (DPTTA-F2TCNQ) to electron (DPTTA-F4TCNQ). This result shows that band engineering can be realized easily in the donor-acceptor complex systems by tuning the electron affinity of the acceptor. The bandgaps of these three complexes vary from 0.31 to 0.41 eV; this narrow bandgap feature is crucial for achieving high thermoelectric performance and the unintentional doping in DPTTA-F4TCNQ leads to the effective suppression of the bipolar cancelling effect on the Seebeck coefficient and the highest power factor.
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