Abdisa, Bedasa (2016) Stability Study and Photovoltaic Application of Quinoxaline Based Polymers and Effect of Low Boiling Point Solvent Additives on Photovoltaic Performance of Bulk Heterojunction Polymer Solar Cells. PhD thesis, Addis Ababa University.
![[img]](http://thesisbank.jhia.ac.ke/style/images/fileicons/application_pdf.png) |
PDF (Stability Study and Photovoltaic Application of Quinoxaline Based Polymers and Effect of Low Boiling Point Solvent Additives on Photovoltaic Performance of Bulk Heterojunction Polymer Solar Cells)
Bedasa, Abdisa(1).pdf - Accepted Version Restricted to Repository staff only Download (2MB) | Request a copy |
Abstract
In this study the photochemical stability and photovoltaic performance of two polymer families are presented; one based on a thiophene-quinoxaline unit and the other one on a thiophene-pyridopyrazine unit. Copolymerization of these monomers together with thiophene-hexylthiophene was performed in order to make the polymers more black, i.e. to fill the gap between the high- and the low-energy peak in the absorption spectra. The study has focused on how an increasing fraction of thiophenehexylthiophene affects the photo-oxidative stability of these polymers, as well as the solar cell performance. Accordingly, thiophene-pyridopyrazine devices displayed increased device efficiency. In addition, the stability is retrained upon inclusion of the extra monomer of 30% and 50% mole fraction of thiophene-hexylthiophene. In contrast, it was found that for the thiophene-quinoxaline based copolymer both, device efficiency and stability, decreased with inclusion of 30%, 50%, and also 80% thiophene-hexylthiophene. Furthermore, the effect of incorporation of low mole fraction of thiophenehexylthiophene i.e 1% and 2.5% in to quinoxaline based polymer on photochemical and photovoltaic performance was also studied. In contrast to the incorporation of large fraction of thiophene-hexylthiophene in to quinoxaline based polymer, incorporation of low fraction of thiophene-hexylthiophene has improved both photochemical stability and photovoltaic performance of the copolymers. Additionally, the effect of low boiling point solvent additives such as iodomethane, iodoethane, and diiodomethane on photovoltaic performance of bulk heterojunction polymer solar cells was studied. According to our findings, the efficiency of TQ1:[60]PCBM based devices have increased from 3.41% (control device) to 4.28, to 4.41, and 4.66% when the devices are processed from 3% (v/v) IMe, IEt, and DIMe, respectively. Similarly, the PCE of PCDTBT:[70]PCBM based devices have also showed enhancement from 3.08% (control device) to 3.39, 3.80, and 4.37% when processed from 3% (v/v) IMe, IEt, and DIMe, respectively. All the solvent additives have improved current density and fill factor leading to enhanced power conversion efficiency compared to control device fabricated without any additive. This is due to formation of nanomorphology creating large D-A interface area for better charge carrier dissociation and interpenetrated networks for efficient charge carrier transport to electrodes as confirmed from the AFM images. As confirmed by comparing UVVis absorption spectra of pristine blend films and blend films soaked in the additives for 5 seconds, the solvent additives selectively dissolved the PCBM aggregates leading to enhancing their misciblity/interaction in to the polymer domains of the active layer. The enhanced misciblity and nanoscale formation of the blends were further confirmed by an increase of the quenching efficiency of the PL of the blends containing the solvent additives compared to the pristine blends. Therefore, the increase in interface area and formation of networks between the donors and acceptors up on addition of the low boiling point solvent additives are the main reasons for the improvement of current density and fill factor leading to enhanced PCEs.
| Item Type: | Thesis (PhD) |
|---|---|
| Subjects: | Q Science > Q Science (General) Q Science > QD Chemistry |
| Divisions: | Africana |
| Depositing User: | Selom Ghislain |
| Date Deposited: | 10 Sep 2018 14:08 |
| Last Modified: | 10 Sep 2018 14:08 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/5114 |
Actions (login required)
 |
View Item |