Impact of Solvent Additive on Carrier Transport in Polymer:Fullerene Bulk Heterojunction Photovoltaic Cells

Carr Hoi Yi Ho, Qi Dong, Hang Yin, Winky Wing Ki Leung, Qingdan Yang, Harrison Ka Hin Lee, Sai Wing Tsang, Shu Kong So*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

45 Citations (Scopus)
14 Downloads (Pure)


The effects of a solvent additive, 1,8-diiodooctane (DIO), on both hole and electron transport are investigated in a state-of-the-art bulk-heterojunction (BHJ) system, namely PTB7:PC71BM. For a polymer:fullerene weight ratio of 1:1.5, the electron mobility in the blend film increases by two orders of magnitude with the DIO concentration while almost no change is found in the hole mobility. For lower DIO concentrations, the electron mobility is suppressed because of large, but poorly connected PC71BM domains. For higher concentrations of DIO, the electron mobility is improved progressively and the hole mobility becomes the limiting factor. Between 1 and 5 vol%, the electron and hole mobilities are balanced. Using the Gaussian disorder model (GDM), we found that the DIO concentration modifies fundamentally the average hopping distances of the electrons. In addition, there exist alternative donor-acceptor ratios to achieve optimized PTB7:PC71BM based solar cells. It is demonstrated that the fullerene content of the BHJ film can be significantly reduced from 1:1.5 to 1:1 while the optimized performance can still be preserved.

Original languageEnglish
Article number1500166
JournalAdvanced Materials Interfaces
Issue number12
Publication statusPublished - 1 Aug 2015

Scopus Subject Areas

  • Mechanics of Materials
  • Mechanical Engineering

User-Defined Keywords

  • admittance spectroscopy
  • bulk heterojunction
  • carrier transport
  • photovoltaics
  • solvent additives


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