Significantly Reduced Thermal-Activation Energy for Hole Transport via Simple Donor Engineering: Understanding the Role of Molecular Parameters for Thermoelectric Behaviors

Fei Zhong; Xiaojun Yin; Zhanxiang Chen; Chunmei Gao; Lei Wang

doi:10.1021/acsami.0c05771

Significantly Reduced Thermal-Activation Energy for Hole Transport via Simple Donor Engineering: Understanding the Role of Molecular Parameters for Thermoelectric Behaviors

ACS Appl Mater Interfaces. 2020 Jun 10;12(23):26276-26285. doi: 10.1021/acsami.0c05771. Epub 2020 Jun 1.

Authors

Fei Zhong¹, Xiaojun Yin¹, Zhanxiang Chen², Chunmei Gao³, Lei Wang¹

Affiliations

¹ Shenzhen Key Laboratory of Polymer Science and Technology, College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China.
² Hubei Key Lab on Organic and Polymeric Optoelectronic Materials, Department of Chemistry, Wuhan University, Wuhan, 430072, P.R. China.
³ College of Chemistry and Chemical Engineering, Shenzhen University, Shenzhen 518060, P.R. China.

PMID: 32421324
DOI: 10.1021/acsami.0c05771

Abstract

Thermal activation energy for charge transfer (E_act,σ) plays a crucial role in determining the electrical properties of organic semiconductors, which are largely dominated by the Coulomb binding energy (E_coul,ICTC) or static energy disorder (σ_ICTC) of the formed integer charge transfer complexes at low or high doping concentration, respectively. Herein, we provide two typical donor-acceptor type polymers with distinct donors to disclose the role of molecular parameters in response for their corresponding thermoelectric (TE) behaviors. Noticeably, both the E_coul,ICTC and σ_ICTC of the polymers can be effectively restrained by varying the initial carbazole (CZ) donor to the dithieno[3,2-b:2',3'-d]pyrrole (DTP) moiety, which contributes to the remarkably decreased E_act,σ values of the PDTP-DPP than that of PCZ-DPP. Accordingly, the optimized power factors (PF) for PDTP-DPP (10.8 μW m^-1 K^-2) is almost 5 times higher than the primary PCZ-DPP (1.8 μW m^-1 K^-2) at ambient condition. In addition, a further improved PF over 85.5 μW m^-1 K^-2 can be achieved by PDTP-DPP at 488 K due to the synergy of thermal-induced dedoping and thermal-activated semiconducting behavior. Ultraviolet photoelectron and X-ray photoelectron spectroscopy measurements confirm the lower thermal activation energy for efficient p-doping of PDTP-DPP than that of PCZ-DPP.

Keywords: integer charge transfer complexes; molecular parameters; p-doping; thermal-activation energy; thermoelectric.