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Surface band bending and carrier dynamics in colloidal quantum dot solids.
Pip C J Clark1, Nathan K Lewis1, Jack Chun-Ren Ke1
1Department of Physics and Astronomy and the Photon Science Institute, The University of Manchester, Manchester M13 9PL, UK. pcjclark@gmail.com.
Nanoscale
|October 20, 2021
Summary
Band bending occurs at the surface of colloidal quantum dot (CQD) solids, impacting device performance. Oxygen contaminants influence carrier dynamics, with faster dynamics observed in specific CQD solids.
Area of Science:
- Materials Science
- Surface Science
- Nanotechnology
Background:
- Band bending in colloidal quantum dot (CQD) solids is crucial for charge transport in devices.
- The presence of intrinsic band bending at the CQD solid-vacuum interface was previously unconfirmed.
Purpose of the Study:
- To investigate intrinsic band bending at the surface of CQD solids.
- To determine the timescales of carrier dynamics at the CQD solid surface.
- To correlate surface chemistry with carrier dynamics.
Main Methods:
- Photoemission surface photovoltage measurements were used to detect surface depletion regions.
- Laser-pump photoemission-probe time-resolved measurements characterized carrier dynamics.
- Surface chemistry analysis identified contaminants.
Main Results:
- Depletion regions were observed at the surface of both n-type and p-type CQD solids across various ligand treatments.
- Carrier dynamics timescales varied significantly, spanning six orders of magnitude.
- Faster dynamics (microseconds) were seen in PbS-MAI/PbI2 solids, while slower dynamics (seconds) occurred in PbS-MPA and PbS-PbI2 solids.
- A correlation was found between slower carrier dynamics and the presence of oxygen contaminants.
Conclusions:
- Intrinsic band bending is present at the surface of CQD solids.
- Oxygen contaminants likely form deep traps, leading to slower surface carrier dynamics.
- Understanding surface band bending and carrier dynamics is essential for optimizing CQD device performance.
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