Acid-Assisted Ligand Exchange Enhances Coupling in Colloidal Quantum Dot Solids

Jea Woong Jo, Jongmin Choi, F. Pelayo García De Arquer, Ali Seifitokaldani, Bin Sun, Younghoon Kim, Hyungju Ahn, James Fan, Rafael Quintero-Bermudez, Junghwan Kim, Min Jae Choi, Se Woong Baek, Andrew H. Proppe, Grant Walters, Dae Hyun Nam, Shana Kelley, Sjoerd Hoogland, Oleksandr Voznyy, Edward H. Sargent*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

58 Scopus citations


Colloidal quantum dots (CQDs) are promising solution-processed infrared-absorbing materials for optoelectronics. In these applications, it is crucial to replace the electrically insulating ligands used in synthesis to form strongly coupled quantum dot solids. Recently, solution-phase ligand-exchange strategies have been reported that minimize the density of defects and the polydispersity of CQDs; however, we find herein that the new ligands exhibit insufficient chemical reactivity to remove original oleic acid ligands completely. This leads to low CQD packing and correspondingly low electronic performance. Here we report an acid-assisted solution-phase ligand-exchange strategy that, by enabling efficient removal of the original ligands, enables the synthesis of densified CQD arrays. Our use of hydroiodic acid simultaneously facilitates high CQD packing via proton donation and CQD passivation through iodine. We demonstrate highly packed CQD films with a 2.5 times increased carrier mobility compared with prior exchanges. The resulting devices achieve the highest infrared photon-to-electron conversion efficiencies (>50%) reported in the spectral range of 0.8 to 1.1 eV.

Original languageEnglish (US)
Pages (from-to)4417-4423
Number of pages7
JournalNano letters
Issue number7
StatePublished - Jul 11 2018


  • Colloidal quantum dots
  • infrared
  • narrow bandgap
  • photovoltaics
  • solution-phase ligand exchange
  • surface passivation

ASJC Scopus subject areas

  • General Chemistry
  • Condensed Matter Physics
  • Mechanical Engineering
  • Bioengineering
  • General Materials Science


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