New Fabrication Approaches for High Efficiency CdS/CdTe Solar Cells

Presented in this thesis are the results from the study of new fabrication approaches for high efficiency thin film CdS/CdTe solar cells grown in superstrate configuration. Hereinafter the phrases CdS/CdTe solar cells and thin film CdS/CdTe solar cell will imply thin film CdS/CdTe solar cell grown in superstrate configuration. This thesis contains four main parts. The first part (chapters 1 and 2) presents general information about thin film CdS/CdTe solar cells, and their place among other types of solar cells. A definition of the device is given and explained. Possible configurations of thin film CdS/CdTe solar cells are shown. A historical overview of the evolution of thin film CdS/CdTe solar cell efficiency from 1969 - advent of the first thin film CdS/CdTe solar cell – up to now is presented. A short overview of the main ongoing research and present challenges is given in the paragraph “Current research directions”. Also included in the first part is the aim of this study defined according to present-day challenges for CdTe photovoltaic. In the second part (chapter 3) the fabrication process for thin film CdS/CdTe solar cells preparation developed in our laboratory by the author is presented. All steps starting from substrate up to the finished working device are mentioned. All the required techniques and materials are specified. Moreover in the second part the experimental techniques, which were used for solar cells characterization, are presented. The operating modes for each type of characterization are also presented. The third part (from chapter 4 to chapter 7) focuses on the new fabrication approaches for thin film CdS/CdTe solar cells. Influence of alternative fabrication steps in lieu of our standard fabrication process steps on solar cells performance is presented. We examined how the performance of CdS/CdTe solar cells is influenced by: different fabrication methods of CdS window layer and different Bromine-Methanol etching. An alternative recrystallization process for low substrate temperature deposited CdTe solar cells was studied. The influence of alternative treatment on CdS/CdTe solar cells behavior and performance is presented. Results are compared with the results from the standard process. Results of this study addressed by tellurium scarcity are presented in chapter 5. Influence of CdTe thickness on structural and electrical properties of CdTe/CdS solar cells was investigated. In chapter 7 flexible solar cells production process developed in our laboratory is presented. Results and challenges addressed by the fabrication of flexible CdTe solar cells by a low temperature process on ITO/ZnO coated polymers are presented in this chapter. In the fourth part all results obtained during this study are summarized and presented. The results have already been partly published in peer-reviewed journals and conferences proceedings.