Bridging the gap between processing and performance : morphological characterization of organic photovoltaics using X-ray methods
Abstract/Contents
- Abstract
- How can we provide renewable energy with low upfront cost and adaptable installation? This is the question that organic photovoltaics (OPV) seek to answer. OPV devices benefit from inexpensive production, flexibility, and low weight. The performance of lab-made devices has been steadily improving, but there is still a barrier to scaling up production. This is because the efficiency of the device depends heavily on the morphology of the active layer as it self-assembles from solution. In this dissertation, I develop and use X-ray methods to measure the morphology of OPV materials in order to link processing, morphology, and performance. I start with an overview of OPV devices, including a summary of morphological parameters that are of interest. Then I outline the characterization strategies that are currently available. I apply these methods to investigate the links between fabrication, morphology, and performance for two fabrication strategies. In the first part, I analyze the effect of various annealing temperatures on a polymeric material. I conclude that moderate-temperature annealing improves the morphology and performance, while high-temperature annealing results in a side chain cleavage reaction which is favorable to morphology but detrimental to performance. This discrepancy is likely caused by reaction by-products remaining in the film. The similarity of this reaction to degradation caused by irradiation gives clues to the burn-in mechanism which has been widely observed in OPV materials. The second part examines the effect of side chain manipulation on morphology and performance in a polymer:fullerene system. I conclude that high performance is achieved through favorable domain sizes, crystallinity, and packing structure, all of which intimately depend on side chain selection. On the other hand, high performance does not require the existence of a mixed phase, which also depends on side chain selection. I also find that the highest performing system benefits from the self-assembly of the polymer into small aggregates, which is aided by its unique side chain configuration. Next, I develop new strategies for analyzing OPV morphology. The first of these describes a software package that I wrote to help researchers analyze various aspects of X-ray scattering data: normalization and uncertainty in scattering intensity, indexing a scattering pattern to extract a crystal structure, and correction of a scattering pattern for refraction. Lastly, I demonstrate that ptychography may be used for measuring OPV morphology with unprecedented resolution and low beam damage when beam energy is decreased.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2019; ©2019 |
| Publication date | 2019; 2019 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Savikhin, Victoria | |
|---|---|---|
| Degree supervisor | Pianetta, Piero | |
| Thesis advisor | Pianetta, Piero | |
| Thesis advisor | Solgaard, Olav | |
| Thesis advisor | Toney, Michael Folsom | |
| Degree committee member | Solgaard, Olav | |
| Degree committee member | Toney, Michael Folsom | |
| Associated with | Stanford University, Department of Electrical Engineering. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Victoria Savikhin. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis Ph.D. Stanford University 2019. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2019 by Victoria Savikhin
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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