Improved performance of molecular bulk-heterojunction photovoltaic cells through predictable selection of solvent additives

Kenneth R. Graham, Patrick M. Wieruszewski, Romain Stalder, Michael J. Hartel, Jianguo Mei, Franky So, John R. Reynolds

Research output: Contribution to journalArticlepeer-review

152 Scopus citations


Solvent additives provide an effective means to alter the morphology and thereby improve the performance of organic bulk-heterojunction photovoltaics, although guidelines for selecting an appropriate solvent additive remain relatively unclear. Here, a family of solvent additives spanning a wide range of Hansen solubility parameters is applied to a molecular bulk-heterojunction system consisting of an isoindigo and thiophene containing oligomer as the electron donor and [6,6]-phenyl-C 61-butyric acid methyl ester (PC 61BM) as the electron acceptor. Hansen solubility parameters are calculated using the group contribution method and compared with the measured solubilities for use as a screening method in solvent additive selection. The additives are shown to alter the morphologies in a semipredictable manner, with the poorer solvents generally resulting in decreased domain sizes, increased hole mobilities, and improved photovoltaic performance. The additives with larger hydrogen bonding parameters, namely triethylene glycol (TEG) and N-methyl-2-pyrrolidone (NMP), are demonstrated to increase the open circuit voltage by ~0.2 V. Combining a solvent additive observed to increase short circuit current, poly(dimethylsiloxane), with TEG results in an increase in power conversion efficiency from 1.4 to 3.3%.

Original languageEnglish
Pages (from-to)4801-4813
Number of pages13
JournalAdvanced Functional Materials
Issue number22
StatePublished - Nov 21 2012


  • molecular bulk-heterojunction
  • morphology
  • organic photovoltaic devices
  • organic solar cells
  • solvent additive processing

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • General Chemistry
  • Condensed Matter Physics
  • General Materials Science
  • Electrochemistry
  • Biomaterials


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