Origin of Unusual Excitonic Absorption and Emission from Colloidal Ag2S Nanocrystals: Ultrafast Photophysics and Solar Cell

Wasim J. Mir, Abhishek Swarnkar, Rituraj Sharma, Aditya Katti, K. V. Adarsh, Angshuman Nag*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

72 Scopus citations

Abstract

Colloidal Ag2S nanocrystals (NCs) typically do not exhibit sharp excitonic absorption and emission. We first elucidate the reason behind this problem by preparing Ag2S NCs from nearly monodisperse CdS NCs employing cation exchange reaction. It was found that the defect-related midgap transitions overlap with excitonic transition, blurring the absorption spectrum. On the basis of this observation, we prepared nearly defect-free Ag2S NCs using molecular precursors. These defect-free Ag2S NCs exhibit sharp excitonic absorption, emission (quantum yield 20%) in near-infrared (853 nm) region, and improved performance of Ag2S quantum-dot-sensitized solar cells (QDSSCs). Samples with lower defects exhibit photoconversion efficiencies >1% and open circuit voltage of ∼0.3 V, which are better compared with prior reports of Ag2S QDSSCs. Femtosecond transient absorption shows pump-probe two-photon absorption above 630 nm and slow-decaying excited state absorption below 600 nm. Concomitantly, open-aperture z-scan shows strong two-photon absorption at 532 nm (coefficient 55 ± 3 cm/GW).

Original languageEnglish (US)
Pages (from-to)3915-3922
Number of pages8
JournalJournal of Physical Chemistry Letters
Volume6
Issue number19
DOIs
StatePublished - Oct 1 2015

Keywords

  • AgS nanocrystals
  • cation exchange
  • excitonic absorption and emission
  • femtosecond transient absorption
  • quantum-dot-sensitized solar cell

ASJC Scopus subject areas

  • General Materials Science
  • Physical and Theoretical Chemistry

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