Ultrafast Kinetics of Chlorinated Polymer Donors: A Faster Excitonic Dissociation Path

Lihe Yan; Zezhou Liang; Jinhai Si; Pingping Gong; Yufei Wang; Xingpeng Liu; Junfeng Tong; Jianfeng Li; Xun Hou

doi:10.1021/acsami.1c24348

Ultrafast Kinetics of Chlorinated Polymer Donors: A Faster Excitonic Dissociation Path

ACS Appl Mater Interfaces. 2022 Feb 9;14(5):6945-6957. doi: 10.1021/acsami.1c24348. Epub 2022 Jan 27.

Authors

Lihe Yan¹, Zezhou Liang¹, Jinhai Si¹, Pingping Gong², Yufei Wang³, Xingpeng Liu², Junfeng Tong², Jianfeng Li², Xun Hou¹

Affiliations

¹ Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of Photonic Technique for Information, School of Electronics Science & Engineering, Faculty of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
² School of Materials Science and Engineering, Gansu Provincial Engineering Research Center for Organic Semiconductor Materials and Application Technology, Lanzhou Jiaotong University, Lanzhou 730070, China.
³ Siyuan Laboratory, Guangzhou Key Laboratory of Vacuum Coating Technologies and New Energy Materials, Department of Physics, Jinan University, Guangzhou 510632, China.

PMID: 35081710
DOI: 10.1021/acsami.1c24348

Abstract

Halogen-substituted donor/acceptor materials are widely regarded as a promising strategy toward improved power-conversion efficiencies (PCEs) in polymer solar cells (PSCs). A chlorinated polymer donor, PClBTA-PS, and its non-chlorinated analogue, PBTA-PS, are synthesized. The PClBTA-PS-based devices show significant enhancements in terms of open-circuit voltage (V_OC = 0.82 V) and fill factor (FF = 76.20%). In addition, a PCE of 13.20% is obtained, which is significantly higher than that for the PBTA-PS-based devices (PCE = 7.63%). Grazing incident wide-angle X-ray scattering shows that the chlorinated polymer enables better π-π stacking in both pure and blend films. DFT and TD-DFT calculations as well as ultrafast photophysics measurements indicate that chlorinated PClBTA-PS has a smaller bonding energy and a longer spontaneous-emission lifetime. The results also reveal that the charge-transfer-state excitons in PClBTA-PS:IT4Cl blend films split into the charge-separated (CS) state via a faster dissociation path, which produces a higher yield of the CS state. Overall, this study provides a deeper understanding of how a halogen-substituted polymer can improve PSCs in the future.

Keywords: density functional theory; excitonic dissociation path; femtosecond time-resolved transient absorption (fs-TA) spectroscopy; halogen-substitution; polymer solar cells.