Band Engineering and Majority Carrier Switching in Isostructural Donor-Acceptor Complexes DPTTA-F X TCNQ Crystals (X = 1, 2, 4)

Yingying Liang; Yunke Qin; Jie Chen; Weilong Xing; Ye Zou; Yimeng Sun; Wei Xu; Daoben Zhu

doi:10.1002/advs.201902456

Band Engineering and Majority Carrier Switching in Isostructural Donor-Acceptor Complexes DPTTA-F _X TCNQ Crystals (X = 1, 2, 4)

Adv Sci (Weinh). 2019 Nov 26;7(3):1902456. doi: 10.1002/advs.201902456. eCollection 2020 Feb.

Authors

Yingying Liang^{1

2}, Yunke Qin^{1

2}, Jie Chen^{1

2}, Weilong Xing^{1

2}, Ye Zou^{1

2}, Yimeng Sun^{1

2}, Wei Xu^{1

2}, Daoben Zhu^{1

2}

Affiliations

¹ Beijing National Laboratory for Molecular Sciences Key Laboratory of Organic Solids Institute of Chemistry Chinese Academy of Sciences Beijing 100190 China.
² University of Chinese Academy of Sciences Beijing 100049 China.

Abstract

Three isostructural donor-acceptor complexes DPTTA-F _X 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.

Keywords: band engineering; donor–acceptor complexes; majority carrier switching; narrow gap; thermoelectric material.