The Department of Physics discussed a Master’s thesis in the field of Pure Sciences submitted by Mohammed Hadi Mahdi Ahmed, entitled:
“A Theoretical Study of the Charge Transfer Reaction Rate in Indoline Dye Contacting TiO₂ Semiconductor.”
The thesis was supervised by Professor Dr. Hadi Jabbar Majeebal and examined by an academic committee comprising Professor Dr. Samira Ahmed Ibrahim, Chair; Assistant Professor Dr. Ronaq Qais Ghadban, Member; Assistant Professor Dr. Nisan Saud Oraibi, Member; and Professor Dr. Hadi Jabbar Majeebal, Member and Supervisor.
The study aimed to develop a theoretical approach for investigating electron-transfer probability and charge-transfer reaction rates in dye-sensitized solar cells (DSSCs) based on D102 indoline dye and titanium dioxide (TiO₂) semiconductor, using quantum transport theory to investigate electron transfer between the dye and semiconductor.
The study also aimed to investigate the effects of the surrounding medium, particularly different solvents, on reorganization energy, coupling strength, and electron-transfer probability, and consequently to evaluate the contact efficiency between D102 dye and the TiO₂ semiconductor.
The thesis adopted a theoretical approach to investigate hybrid dye-sensitized solar-cell systems consisting of D102 dye coupled to TiO₂ semiconductor and surrounded by different solvents, including dimethoxyethane, dichloromethane, tert-butyl alcohol, 1-butanol, ethanol, and methanol.
The study employed a quantum donor–acceptor scenario to simulate electron transfer from the excited state of D102 dye to the conduction band of the TiO₂ semiconductor. Reorganization energy was calculated using a semiclassical approach based on the relevant energy levels of the dye and semiconductor.
MATLAB was used to perform the theoretical calculations and analyze several parameters associated with charge-transfer processes, including reorganization energy, coupling strength, charge-carrier concentration, and electron-transfer probability.
Key Findings
The findings demonstrated that electron-transfer probability is significantly influenced by reorganization energy, coupling strength, charge-carrier concentration, and the properties of the surrounding solvent medium.
The study showed that electron-transfer probability increased with increasing concentration, reaching its highest value at a concentration of 7 × 10¹⁸ cm⁻³. It also increased with increasing coupling strength, reaching a maximum value of 1.244 × 10⁻⁶ eV, according to the reported results.
The findings indicated that dye-sensitized solar cells exhibited improved performance at higher coupling strength and increased charge-carrier concentration. In particular, a concentration of 7 × 10¹⁸ cm⁻³ provided a noticeably higher efficiency compared with a concentration of 2 × 10¹⁸ cm⁻³.
The study also revealed differences in the effects of the investigated solvents on electron-transfer processes. The D102-TiO₂ cells showed notable sensitivity to ethanol and methanol compared with some of the other solvents, while dichloromethane (DCM) produced the lowest electron-voltage transfer among the investigated cases.
The results further demonstrated that increasing coupling strength and charge-carrier concentration enhances electron transfer from excited D102 dye molecules to the TiO₂ semiconductor. Changes in these parameters can therefore directly influence solar-cell performance and charge-transfer efficiency.
The significance of the study lies in applying theoretical modeling and quantum transport theory to understand charge-transfer mechanisms in dye-sensitized solar cells. This provides a scientific basis for investigating the factors governing electron-transfer processes between organic dyes and semiconductor materials.
The findings contribute to a deeper theoretical understanding of the relationship between reorganization energy, coupling strength, charge-carrier concentration, solvent environment, and the performance of dye-sensitized solar cells. Such knowledge may support future efforts to develop more efficient materials and systems for solar-energy conversion.
The thesis is directly aligned with Sustainable Development Goal 7 (SDG 7): Affordable and Clean Energy, through its investigation of dye-sensitized solar cells and the factors governing electron transfer and solar-energy conversion efficiency.
The research is also closely related to Sustainable Development Goal 9 (SDG 9): Industry, Innovation and Infrastructure, through the application of quantum theory and computational modeling to the investigation of advanced materials and systems with potential applications in renewable-energy technologies.
The study also contributes indirectly to Sustainable Development Goal 13 (SDG 13): Climate Action, as the development of more efficient solar-energy conversion technologies can contribute in the future to greater reliance on renewable energy sources and reduced dependence on conventional energy sources associated with higher carbon emissions.
The thesis highlights the importance of theoretical physics research in supporting the development of renewable-energy technologies by providing deeper insight into the microscopic and quantum processes governing charge transfer within solar cells, thereby contributing to future efforts to improve their performance and efficiency.
