Studies on zinc oxide nanostructures for dye sensitized type solar cells and photocatalysis applications | |
| Author | Bora, Tanujjal |
| Call Number | AIT Diss. no.ISE-12-20 |
| Subject(s) | Zinc oxide Nanostructures |
| Note | A dissertation submitted in partial fulfillment of the requirementsfor the degree of Doctor of Engineering in Nanotechnology, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ISE-12-20 |
| Abstract | Nanostructures of zinc oxide (ZnO) were synthesized and used for dye sensitized type solar cells and photocatalysis applications. Hydrothermal technique was used for the synthesis of vertically aligned ZnO nanorods, which were sensitized with ruthenium complex dye N719 to fabricate dye sensitized solar cells (DSSCs). Reduction of native defects in the hydrothermally grown ZnO nanorods by a post annealing treatment was found to play an important role in the performance ofthe DSSCs, analyzed by using a one-diode model equivalent circuit for DSSCs. For the improvement in the DSSC performance, gold (Au) nanoparticles were incorporated in the ZnO nanorod photoelectrodes in order to reduce back electron transfer at the photoelectrode. From the picosecond-resolved, time-correlated singlephotoncount (TCSPC)studies, it was found that the electron injection dynamics in both the bare ZnO and ZnO/Au nanocomposite photoelectrodes is relatively similar; however, the ZnO/Au nanocomposite photoelectrodes exhibited aslower fluorescence decayassociated with the electron recombination processindicating lower interfacial charge recombinations due to the formation of a Schottky barrier at the ZnO/Au interface.Applications of porphyrin molecules to harvest solar energy efficiently and cost effectively is an upcoming research area in the field of DSSCs. The ZnO nanostructures were sensitized with hematoporphyrin (HP) in order to develop a potential light harvesting electrode for efficientDSSCs as well as visible light photocatalysis. Hematoporphyrin molecules conjugated to the ZnO nanostructures through the carboxylic groups of HP. Efficient fluorescence quenching of HP in the resulting HP-ZnO nanorods implied ultrafast electron migrationprocess from photoexcited HP to ZnO nanorods and this photoinduced event find its application in the utilization of the HP-ZnO nanostructures for the fabrication of efficient DSSCs. The photocatalytic degradation of a dye, methylene blue, under visible light irradiation was studied in the presence of oxygen where the photocatalytic activity was found to be influenced by HP sensitization time and the presence of inert gas.ZnO nanorods were further used to fabricate cadmium sulfide (CdS) quantum dot sensitized solar cells (QDSSCs), where the CdS QDs were synthesized in-situ on the surface of the ZnO nanorods. The performance of the CdS QDSSCs was found to be enhanced with the post annealing treatment of the CdS QDs, attributed mainly to the annealing of the defects in the QDs. In order to improve the charge transfer process in the photoelectrode, a core/shell type photoelectrode was developed with ZnO nanorods as core and zinc stannate as shell layer, which exhibited enhanced device efficiency compared to the bare ZnO nanorods owing to the higher surface area and improved charge separation at the core/shell nanorod arrays.In recent years, nanotechnology has gained significant interest for various applications in the medical field. In this regard, utilization of ZnO nanoparticles for the efficient degradation of bilirubin (BR) via photocatalysis technique was explored. BR is a water insoluble byproduct of heme catabolism and can cause jaundice when its excretion is ivimpaired. The ZnO nanoparticle activated photocatalytic degradation of BR through a non-radiative energy transfer pathway was greatly influenced by the surface defect states (mainly oxygen vacancies) of the nanoparticles. The possible mechanism of energy transfer process between the ZnO nanoparticles and the surface adsorbed BR molecules has been studied through picosecond-resolved TCSPC technique. Correlation of photocatalytic degradation and TCSPC studies showed that the defect engineered ZnO nanoparticles obtained through annealing, led to an efficient decomposition of BR molecules enabled by Förster resonance energy transfer (FRET) process. |
| Year | 2012 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ISE-12-20 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Industrial Systems Engineering (DISE) |
| Academic Program/FoS | Industrial Systems Engineering (ISE) |
| Chairperson(s) | Dutta, Joydeep; |
| Examination Committee(s) | Kumar, Sivanappan ;Chanchana Thanachayanont; |
| Scholarship Donor(s) | Sheikh Saqr Al Qasimi Graduate Research Fellowship, United Arab Emirates; |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2012 |