Lan, Fei
(2018)
FUNDAMENTALS OF KELVIN PROBE FORCE MICROSCOPY AND ITS
APPLICATIONS IN THE CHARACTERIZATION OF SOLAR CELLS.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Kelvin probe force microscopy (KPFM) is capable of detecting surface potential (SP) distribution of various materials in nanoscales. Such technique provides quantitative basis for the analysis of electronic properties such as band alignment of semiconductors, junction structure of solar cells and work function of materials. However, because electrostatic force is a long-range force, SP images obtained by KPFM is usually a distorted and blurred reproduction of the real SP distribution of the sample. In this work, KPFM imaging system is modeled as a time-invariant system with measurement equals the convolution of the point spread function (PSF) of the KPFM system with the true SP distribution of the sample. To reverse the distortion, PSF of the KPFM system is first calibrated by comparing the SP distribution of a calibration electrode pair measured by KPFM and the ideal SP distribution simulated with COMSOL. Then, with the calibrated PSF, a non-linear algorithm based on total variation regularization is implemented to reconstruct the SP distribution from the measurements.
In addition, the applications of KPFM in the characterization of solar cells are demonstrated in this work. First, KPFM system is utilized to clarify the electrical role of single walled carbon nanotube (SWNT) in organic solar cells. Usually, SWNTs are introduced in organic solar cells to improve the carrier mobility in these cells. However, the charge transport mechanisms between SWNTs and polymers in organic solar cells are unclear. To clarify the problem, KPFM is utilized in the observation of the SP change in SWNTs when they are placed in hole-enriched and electron-enriched environment. By comparing the SP change of SWNTs, charge transport mechanisms between SWNTs and polymers in organic solar cells are revealed. Finally, KPFM is utilized in the characterization of the cross-sectional surface of planar perovskite solar cells. With the SP profiles of the cross-sectional surface, electric field, junction structures as well as charge injection barriers inside the cells are revealed. These characterizations contribute to the in-depth understanding of the working mechanisms of the solar cell devices, which are valuable for their further optimization.
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| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
25 January 2018 |
| Date Type: |
Publication |
| Defense Date: |
7 April 2017 |
| Approval Date: |
25 January 2018 |
| Submission Date: |
26 August 2017 |
| Access Restriction: |
5 year -- Restrict access to University of Pittsburgh for a period of 5 years. |
| Number of Pages: |
111 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Electrical Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Kelvin Probe Force Microscopy; Solar cells; Point spread function; Deconvolution; Carbon nanotube |
| Date Deposited: |
25 Jan 2018 21:30 |
| Last Modified: |
25 Jan 2023 06:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/33152 |
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