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Study of Exciton Hopping Transport in PbS Colloidal Quantum Dot Thin Films Using Frequency- and Temperature-Scanned Photocarrier Radiometry

  • Lilei Hu
  • Andreas Mandelis
  • Alexander Melnikov
  • Xinzheng Lan
  • Sjoerd Hoogland
  • Edward H. Sargent
ICPPP 18
Part of the following topical collections:
  1. ICPPP-18: Selected Papers of the 18th International Conference on Photoacoustic and Photothermal Phenomena

Abstract

Solution-processed colloidal quantum dots (CQDs) are promising materials for realizing low-cost, large-area, and flexible photovoltaic devices. The study of charge carrier transport in quantum dot solids is essential for understanding energy conversion mechanisms. Recently, solution-processed two-layer oleic-acid-capped PbS CQD solar cells with one layer treated with tetrabutylammonium iodide (TBAI) serving as the main light-absorbing layer and the other treated with 1,2-ethanedithiol (EDT) acting as an electron-blocking/hole-extraction layer were reported. These solar cells demonstrated a significant improvement in power conversion efficiency of 8.55% and long-term air stability. Coupled with photocarrier radiometry measurements, this work used a new trap-state mediated exciton hopping transport model, specifically for CQD thin films, to unveil and quantify exciton transport mechanisms through the extraction of hopping transport parameters including exciton lifetimes, hopping diffusivity, exciton detrapping time, and trap-state density. It is shown that PbS-TBAI has higher trap-state density than PbS-EDT that results in higher PbS-EDT exciton lifetimes. Hopping diffusivities of both CQD thin film types show similar temperature dependence, particularly higher temperatures yield higher hopping diffusivity. The higher diffusivity of PbS-TBAI compared with PbS-EDT indicates that PbS-TBAI is a much better photovoltaic material than PbS-EDT. Furthermore, PCR temperature spectra and deep-level photothermal spectroscopy provided additional insights to CQD surface trap states: PbS-TBAI thin films exhibit a single dominant trap level, while PbS-EDT films with lower trap-state densities show multiple trap levels.

Keywords

CQD solar cells Detrapping lifetime Exciton lifetimes Hopping transport Hopping diffusivity Lead sulfide (PbS)colloidal quantum dot Photocarrier radiometry (PCR) Trap states 

Notes

Acknowledgments

The support of the Canada Research Chairs and the Natural Sciences and Engineering Research Council of Canada (NSERC) through a Discovery Grant to AM is gratefully acknowledged.

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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  • Lilei Hu
    • 1
  • Andreas Mandelis
    • 1
    • 2
  • Alexander Melnikov
    • 1
  • Xinzheng Lan
    • 2
  • Sjoerd Hoogland
    • 2
  • Edward H. Sargent
    • 2
  1. 1.Center for Advanced Diffusion-Wave and Photoacoustic Technologies (CADIPT), Department of Mechanical and Industrial EngineeringUniversity of TorontoTorontoCanada
  2. 2.Edward S. Rogers Sr. Department of Electrical and Computer EngineeringUniversity of TorontoTorontoCanada

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