Controlled Steric Hindrance Enables Efficient Ligand Exchange for Stable, Infrared-Bandgap Quantum Dot Inks

Mengxia Liu, Fanglin Che, Bin Sun, Oleksandr Voznyy, Andrew Proppe, Rahim Munir, Mingyang Wei, Rafael Quintero-Bermudez, Lilei Hu, Sjoerd Hoogland, Andreas Mandelis, Aram Amassian, Shana O. Kelley, F. Pelayo Garciá De Arquer, Edward H. Sargent

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

Colloidal quantum dots (CQDs), which benefit from a size-tuned bandgap, are a solution-processed material for infrared energy harvesting. This characteristic enables the fabrication of solar cells that form tandem devices with silicon. Unfortunately, in the case of CQDs having diameters sufficiently large (>4 nm) so that the nanoparticles absorb light well beyond silicon's bandgap, conventional ligand exchanges fail. Here we report a strategy wherein short-chain carboxylates, used as a steric hindrance controller, facilitate the ligand exchange process on small-bandgap CQDs. We demonstrate that the net energy barrier to replace original capping ligands with lead halide anions is decreased when short carboxylates are involved. The approach produces more complete ligand exchange that enables improved packing density and monodispersity. This contributes to a 2-fold reduction in the trap state density compared to the best previously reported exchange. We demonstrate solar cells that achieve a record infrared photon-to-electron conversion efficiency at the excitonic peak.
Original languageEnglish (US)
Pages (from-to)1225-1230
Number of pages6
JournalACS Energy Letters
Volume4
Issue number6
DOIs
StatePublished - Apr 30 2019

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