Abstract
Colloidal quantum dots (CQDs) are attractive materials for inexpensive, room-temperature-, and solution-processed optoelectronic devices. A high carrier diffusion length is desirable for many CQD device applications. In this work we develop two new experimental methods to investigate charge carrier diffusion in coupled CQD solids under charge-neutral, i.e., undepleted, conditions. The methods take advantage of the quantum-size-effect tunability of our materials, utilizing a smaller-bandgap population of quantum dots as a reporter system. We develop analytical models of diffusion in 1D and 3D structures that allow direct extraction of diffusion length from convenient parametric plots and purely optical measurements. We measure several CQD solids fabricated using a number of distinct methods and having significantly different doping and surface ligand treatments. We find that CQD materials recently reported to achieve a certified power conversion efficiency of 7% with hybrid organic-inorganic passivation have a diffusion length of 80 ± 10 nm. The model further allows us to extract the lifetime, trap density, mobility, and diffusion coefficient independently in each material system. This work will facilitate further progress in extending the diffusion length, ultimately leading to high-quality CQD solid semiconducting materials and improved CQD optoelectronic devices, including CQD solar cells. © 2013 American Chemical Society.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 5282-5290 |
| Number of pages | 9 |
| Journal | ACS Nano |
| Volume | 7 |
| Issue number | 6 |
| DOIs | |
| State | Published - May 31 2013 |
| Externally published | Yes |
Bibliographical note
KAUST Repository Item: Exported on 2020-10-01Acknowledged KAUST grant number(s): KUS-11-009-21
Acknowledgements: This publication is based in part on work supported by Award KUS-11-009-21, made by King Abdullah University of Science and Technology (KAUST), by the Ontario Research Fund Research Excellence Program, and by the Natural Sciences and Engineering Research Council (NSERC) of Canada. David Zhitomirsky would like to acknowledge his NSERC CGS D scholarship. We thank Angstrom Engineering, Inc. and Innovative Technology, Inc. for useful discussions regarding material deposition methods and control of the glovebox environment, respectively. The authors would like to acknowledge P. Maraghechi for aid in ellipsometry measurements and technical assistance from E. Palmiano, R. Wolowiec, and D. Kopilovic.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.