- Title
- Novel approaches to improve device performances of nanoparticle organic solar cells
- Creator
- Chowdhury, Riku
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Organic photovoltaic (OPV) technology has been introduced as an alternative to conventional silicon photovoltaics. Although the state-of-the–art power conversion efficiency (PCE) of OPV surpassed 17% from a single-junction OPV device (PCE of 17.6%) in January 2020, a major issue for this type of OPV is their use of hazardous halogenated solvents for the photoactive layer processing, which limits the commercialization of OPV technology because of environmental and human health concerns. Therefore, processing with eco-friendly solution-processable photoactive materials is a necessary step toward the large-scale commercialization of OPV technology. Alternative approaches using water and other “green” solvents as the solvent may be more suitable for large-scale OPV production. This approach has been projected to enable the opportunity to recycle solvents and hence cut down the manufacturing cost. However, organic semiconductors are poorly soluble in water, therefore dispersion of organic materials into the water-like polar solvent via a surfactant-based miniemulsion process is a smart strategy to overcome this limitation. Initial studies of aqueous processed sodium dodecyl sulphate (SDS) surfactant-based donor:acceptor nanoparticle (NP) ink found that the phase separated core-shell morphology induced in the resultant NPs led to poor exciton dissociation and charge transport in the photoactive layer. Thus, the performance of the nanoparticulated OPV (NP-OPV) is much less efficient than that of the halogenated solvent processed OPV counterpart. This thesis has explored three novel options to address the above-mentioned issues with (1) modified miniemulsion, (2) surfactant engineering and (3) implementation of plasmonic nanostructure. The first study created a more blended intra- and inter-particle morphology of P3HT:PC61BM nanoparticles prepared through a modified miniemulsion method with a vacuum assisted solvent removal technique. This modified miniemulsion method led to an improvement in photoactive layer morphology, as well as a significant reduction (about 5-fold) in NP synthesis time. A combination of field emission secondary electron microscope (FESEM), UV-visible (UV-vis) spectroscopy and scanning transmission X-ray microscopy (STXM) measurements revealed a nanoparticle morphology comprised of highly blended donor-acceptor domains compared to the core-shell conventional miniemulsion processed NP morphology. Therefore, the improved NP morphology boosted the NP-OPV device performance by 27% and 48% using Ca and ZnO as the electron transport layer (ETL) respectively, compared to the reference NP-OPV device. In the second study, a new surfactant, 2-(3-thienyl) ethyloxybutylsulfonate (TEBS) used to synthesise the P3HT:PC61BM NPs. The physical and chemical properties of the TEBS-based NPs were investigated using FESEM, UV-Vis, X-ray diffraction (XRD) and STXM methods. For the first time, the internal chemical composition of TEBS NPs was identified as having an intermixed P3HT:PCBM NP morphology using STXM chemical composition mapping, which is altered from the conventional core-shell morphology of SDS NPs. A systematic examination has been executed to carefully refine the NP production to achieve the best device performance. Devices fabricated from optimized TEBS stabilised P3HT:PC61BM NPs have improved PCE, about 25% higher than that of SDS based NP-OPV devices. The enhancement of TEBS NP-OPV devices was verified by the EQE measurement with about 26% augmentation of photocurrent generation over the corresponding SDS NP-OPV device. Finally, the addition of plasmonic nanoparticles has been implemented to improve the poor exciton dissociation efficiency which is generally observed in aqueous processed NP-OPV devices. Relatively low-cost NaxWO3 plasmonic nanoparticles were imbedded into the electron transfer layer of NP-OPV devices. By carefully controlling the mixing ratio of the absolute weight concentration of NaxWO3 and ZnO in the cathodic interfacial layer, the optical absorbance of the NP-OPV device can be improved by about 15% which leads to an enhanced EQE. The JSC of the best NP-OPV device was found to be amplified by about 12.5% and ultimately, the PCE of the corresponding NP-OPV device was boosted ⁓35% compared to the standard NP-OPV device. Further investigation of the maximum exciton generation rate and probability of exciton dissociation in the hero NP-OPV devices showed that these parameters increased by around 21.5% and 6.6% correspondingly, confirming the effect of NaxWO3 nanoparticles of enhancing the performance of NP-OPV device. In addition, recorded PL data was consistent with the calculated maximum exciton generation rate at the optimized mixing ratio of NaxWO3:ZnO used in the NP-OPV devices. The overall results indicate that enhancement in light absorption of the water-processed photoactive layer by scattering and Localized Surface Plasmonic Resonance (LSPR) effects increase the exciton generation rate and the probability of exciton dissociation, which play critical roles in charge generation in the water-processed NP-OPV device.
- Subject
- nanoparticle organic solar cells; modified miniemulsion process; surfactant engineering; intermixed donor:acceptor morphology; plasmonic nanoparticles
- Identifier
- http://hdl.handle.net/1959.13/1460972
- Identifier
- uon:46077
- Rights
- Copyright 2021 Riku Chowdhury
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT01 | Thesis | 7 MB | Adobe Acrobat PDF | View Details Download | ||
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