M.Sc Thesis


M.Sc StudentIdo Winer
SubjectSol Gel Synthesis of Doped ZnO Transperent Electrodes for
Photovoltaic cells
DepartmentDepartment of Chemical Engineering
Supervisors Full Professors Grader Gideon
Dr. Shter Gennady
Full Thesis textFull thesis text - English Version


Abstract


An important component of thin-film PV cells is the Transparent Conducting Oxide (TCO) layer, which acts as a front electrode of the PV absorber. The most common TCO material is ITO, (Indium-Tin oxide), which demonstrates good electrical and optical properties. However, the high cost of Indium limits its wide industrial implications. Zinc oxide is a promising alternative TCO material due to its excellent transparency, good conductivity, and low-cost.

Today most of TCOs are deposited by high cost methods. The sol-gel method is a simple and robust technology, offering a reliable and relatively simple property control. The use of the Sol-Gel coating method enables an excellent control on TCO's properties, and can reduce manufacturing cost compared to other methods. In addition, this method can be applied easily to large areas, required for industrial applications of PV devices.

The goal of this work was to develop a sol-gel derived ZnO transparent electrode. The main purpose was to investigate the influence of the different process parameters on the film’s final properties. By understanding the influences of each parameter, we intended to create a film with the most suitable properties to act as a TCO film inside a solar cell.

The influence of heat treatments on the layer was studied. We found out that higher sintering temperature improve the nanostructure of the film and reduces its porosity. However, too high temperatures damaged the films creating macro-defects and harming the conductivity.

We investigated the influence of different solution parameters, including precursor salt, solvent and stabilizer. We saw that each parameter has a very significant influence on the film’s properties. The optimal results were received when using zinc acetate as a salt, 2-methoxyethanol  as a solvent and monoethanolamine as a stabilizer.

An attempt was made to implement the films inside a dye sensitized solar cell. The attempt wasn’t successful because of the aggressive nature of the electrolyte used in the solar cell. Few attempts to solve the problem improved the results but still we weren’t able to reach the desired results using the iodine based electrolyte.

Films with a thickness of 50-600nm were deposited, the films showed excellent transmittance of ~90% in the visible and near IR region. In most cases a c-axis preferred orientation, which is typical for ZnO films. Films showed sheet resistance that varied significantly according to the process parameters, while the best result was of 68 Ω/sqr.