- Title
- Investigation of thermally induced morphological changes in organic photovoltaic devices
- Creator
- Routley, Ben Stephen
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2019
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- This thesis aimed to develop optical-based techniques for studying the active layer morphology and performance of organic photovoltaic devices. The results obtained from these techniques have lead to the development of models to explain the mechanisms of the phase separation observed in the active layer. In the first experimental chapter, the development of a near-field optics based photocurrent mapping measurement technique is presented. This technique is an extension of the established near-field scanning photocurrent mapping (NSPM) technique. It is postulated that by performing NSPM using multiple wavelengths simultaneously, quantitative chemical composition information could be obtained. Initially, a technique that sequentially switched the measurement wavelength is developed. However, this switching leads to thermal flexing of the NSPM probe rendering the technique unsuitable. To alleviate this flexing the sequential method is replaced with frequency division multiplexing (FDM). Using this FDM approach the developed multi-wavelength near-field scanning photocurrent mapping (MWNSPM) technique is used to identify the phase separation occurring in a poly(9,9-dioctyl- fluorene-2,7-diyl-co-bis-N,N’-(4-butylphenyl)-bis-N,N’-phenyl-1,4-phenylenedi-amine) (PFB) : poly(9,9-dioctyl_uorene-2,7-diyl-co-benzothiadiazole) (F8BT) blend film. Although MWNSPM is capable of identifying rich regions of these two species, no quantitative chemical information is obtained. In the second experimental chapter, the development of the multi-wavelength scanning absorption mapping (MWSAM) technique is presented. This technique measured the optical absorption for multiple wavelengths forming absorption maps. These maps are used to solve a set of simultaneous equations to obtain the film’s optical thickness and chemical composition. MWSAM is used to obtain quantitative chemical information for a poly-3-hexylthiophene (P3HT) : [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) film, with the results self-consistent with film’s manufacturing conditions. The established technique scanning transmission X-ray microscopy (STXM) also utilises absorption to measure the film’s thickness and chemical composition. Hence a comparison between the results obtained by MWSAM and published STXM results is made, with the MWSAM results comparing favourably. In the third experimental chapter, the MWSAM technique is extended to allow for the measurement of the absorption and photocurrent maps simultaneously. The same set of simultaneous equations used by MWSAM are used to obtain the film’s thickness and chemical composition. However, unlike MWSAM the device’s local EQE and IQE are measured, allowing for a direct comparison between the local morphology and local performance; this technique is termed multi-wavelength scanning absorption mapping (MWSPAM). Analysis of the local morphology and local performance establishes the presence of enhanced charge transfer states forming for the 650 nm excitation. In the fourth experimental chapter, the developed MWSPAM technique is used to study a series of P3HT:PCBM based OPVs with different annealing times. It is shown that the microstructure of the OPV’s active layer will undergo large-scale evolution when thermally annealed, with large-scale phase separation of the P3HT and PCBM occurring. Additionally, a factor that indicates the performance of P3HT and PCBM in a given morphology is determined. In the final experimental chapter, further analysis of the series of annealed OPVs is conducted, leading to the development of several algorithms to calculate information relating to the formation of PCBM aggregates. This information is used in conjunction with the data presented throughout the thesis to hypothesise a diffusion model for PCBM crystallites that form in the P3HT:PCBM film.
- Subject
- organic photovoltaic devices; near-field optics; scanning absorption mapping; photocurrent mapping
- Identifier
- http://hdl.handle.net/1959.13/1400454
- Identifier
- uon:34773
- Rights
- Copyright 2019 Ben Stephen Routley
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 17 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 223 KB | Adobe Acrobat PDF | View Details Download |