Charge Photogeneration and Recombination in Fluorine-Substituted Polymer Solar Cells

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.

Photoelectric Conversion and Device Stability of PM6:PY-IT Solar Cells Based on a Water Solution-Processed MoO3 Hole Transport Layer

“…The device architecture of all-polymer solar cells employed the classical conventional configuration, that is, the ITO/MoO 3 or PEDOT:PSS/PM6:PY-IT/LiF/Al structure. The cleaning process of ITO glass was carried out according to the literature. , Subsequently, the ITO substrate was dried and ultraviolet ozone-treated for 10 min. After that, the MoO 3 precursor solution (or PEDOT:PSS) was spin-coated on the ITO substrate at 4000 rpm for 30 s. Then, the wet film was annealed at 300 °C for 30 min to form the MoO 3 film, whereas the PEDOT:PSS layer with a thickness of ∼25 nm was annealed at 150 °C for 15 min in air .…”