Charge Photogeneration and Recombination in Fluorine-Substituted Polymer Solar Cells

Rong Hu; Yurong Liu; Jun Peng; Jianjun Jiang; Mengyao Qing; Xiaochuan He; Ming-Ming Huo; Wei Zhang

doi:10.3389/fchem.2022.846898

Charge Photogeneration and Recombination in Fluorine-Substituted Polymer Solar Cells

Front Chem. 2022 Feb 24:10:846898. doi: 10.3389/fchem.2022.846898. eCollection 2022.

Authors

Rong Hu¹, Yurong Liu¹, Jun Peng², Jianjun Jiang², Mengyao Qing², Xiaochuan He³, Ming-Ming Huo⁴, Wei Zhang^{2

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Affiliations

¹ School of Materials Science and Engineering, Chongqing University of Arts and Sciences, Chongqing, China.
² School of Physics and Materials Science, Guangzhou University, Guangzhou, China.
³ Songshan Lake Materials Laboratory, Dongguan, China.
⁴ Qingdao Branch, Naval Aeronautical University, Qingdao, China.
⁵ Research Center for Advanced Information Materials (CAIM), Huangpu Research and Graduate School of Guangzhou University, Guangzhou, China.
⁶ Guangzhou University-Linköping University Research Center on Urban Sustainable Development, Guangzhou University, Guangzhou, China.

Abstract

In this contribution, we studied the effect of fluorine substitution on photogenerated charge generation, transport, and recombination in polymer solar cells. Two conjugated polymer materials, PBDTTT-E (fluorine free) and PTB7 (one fluorine substitution), were compared thoroughly. Meanwhile, various characterization techniques, including atomic force microscopy, steady-state spectroscopy, transient absorption spectroscopy, spectroelectrochemistry, and electrical measurements, were employed to analyse the correlation between molecular structure and device performance. The results showed that the influence of fluorine substitution on both the exciton binding energy of the polymer and the carrier recombination dynamics in the ultrafast timescale on the polymer was weak. However, we found that the fluorine substitution could enhance the exciton lifetime in neat polymer film, and it also could increase the mobility of photogenerated charge. Moreover, it was found that the SOMO energy level distribution of the donor in a PTB7:PC71BM solar cell could facilitate hole transport from the donor/acceptor interface to the inner of the donor phase, showing a better advantage than the PBDTTT-E:PC71BM solar cell. Therefore, fluorine substitution played a critical role for high-efficiency polymer solar cells.

Keywords: charge recombination; charge transport; fluorine substitution; polymer solar cells; power conversion efficiency.