Importance of Electric-Field-Independent Mobilities in Thick-Film Organic Solar Cells

Carr Hoi Yi Ho*, Yusen Pei, Yunpeng Qin, Chujun Zhang, Zhengxing Peng, Indunil Angunawela, Austin L. Jones, Hang Yin, Hamna F. Iqbal, John R. Reynolds, Kenan Gundogdu, Harald Ade, Shu Kong So, Franky So*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

9 Citations (Scopus)


In organic solar cells (OSCs), a thick active layer usually yields a higher photocurrent with broader optical absorption than a thin active layer. In fact, a ∼300 nm thick active layer is more compatible with large-area processing methods and theoretically should be a better spot for efficiency optimization. However, the bottleneck of developing high-efficiency thick-film OSCs is the loss in fill factor (FF). The origin of the FF loss is not clearly understood, and there a direct method to identify photoactive materials for high-efficiency thick-film OSCs is lacking. Here, we demonstrate that the mobility field-dependent coefficient is an important parameter directly determining the FF loss in thick-film OSCs. Simulation results based on the drift-diffusion model reveal that a mobility field-dependent coefficient smaller than 10-3(V/cm)-1/2is required to maintain a good FF in thick-film devices. To confirm our simulation results, we studied the performance of two ternary bulk heterojunction (BHJ) blends, PTQ10:N3:PC71BM and PM6:N3:PC71BM. We found that the PTQ10 blend film has weaker field-dependent mobilities, giving rise to a more balanced electron-hole transport at low fields. While both the PM6 blend and PTQ10 blend yield good performance in thin-film devices (∼100 nm), only the PTQ10 blend can retain a FF = 74% with an active layer thickness of up to 300 nm. Combining the benefits of a higher JSCin thick-film devices, we achieved a PCE of 16.8% in a 300 nm thick PTQ10:N3:PC71BM OSC. Such a high FF in the thick-film PTQ10 blend is also consistent with the observation of lower charge recombination from light-intensity-dependent measurements and lower energetic disorder observed in photothermal deflection spectroscopy.

Original languageEnglish
Pages (from-to)47961-47970
Number of pages10
JournalACS Applied Materials and Interfaces
Issue number42
Early online date26 Oct 2022
Publication statusPublished - 26 Oct 2022

Scopus Subject Areas

  • Materials Science(all)

User-Defined Keywords

  • electric field
  • field dependence
  • fill factor
  • mobility
  • organic photovoltaic
  • thick film


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