Degree Granting Department
Christos S. Ferekides, Ph.D.
Don L. Morel, Ph.D.
Yun L. Chiou, Ph.D.
Semiconductors, Thin films, Transparent conducting materials, Sputtering, Interdiffusion
The electrical conductivity of transparent conducting oxides is well exploited in front surface electrodes for solar cells where high transmission is also important. Fluorine doped tin oxide (SnO2: F) is the most popular choice of front contacts for CdTe solar cells. In this thesis, Cd2SnO4 and Zn2SnO4 thin films are investigated focusing on their electrical and optical properties and used them in solar cells. Processing for these materials is optimized for optimum solar cell performance.
Cd2SnO4 thin films are deposited by co-sputtering of CdO and SnO2 targets in Ar ambient at room temperature. Then films are subjected to high temperature annealing in He ambient. The films crystallize in inverse spinel structure. The average transmission of a Cd2SnO4 thin film with a thickness of 2500Å obtained in this study is 92%. The lowest resistivity obtained in this work for a Cd2SnO4 film with a thickness of 2500Å is 5.4 X 10-4 Ω-cm. The effect of stoichiometry on structure, optical and electrical properties of Cd2SnO4 is studied by varying the amount of CdO and SnO2 in the Cd2SnO4 film.
Zinc stannate thin films are deposited by co-sputtering of ZnO and SnO2 targets in Ar ambient at both room temperature and elevated temperatures. As deposited and high temperature annealed Zn2SnO4 thin films are highly resistive. The average transmission x of a Zn2SnO4 thin film with a thickness of 2000Å and annealed at 600°C in He has been 94%. Zn2SnO4 thin films are incorporated as a buffer layers into CdTe solar cells. SnO2: F is used as a front contact in CdTe solar cells in conjunction with high resistive Zn2SnO4 buffer layer.
The best SnO2:F /zinc stannate cell device performance for room temperature deposited zinc stannate film resulted for the device with Zn/Sn =2.1. It has an efficiency of 12.43% with VOC = 810mV, FF = 66.6% and JSC = 23.1 mA. The best SnO2:F /zinc stannate cell device performance for Zn2SnO4 thin film deposited at 400°C resulted for the device with 500Å thick zinc stannate. It has an efficiency of 14.21% with VOC = 830mV, FF = 69.3% and JSC = 24.74 mA
Scholar Commons Citation
Gayam, Sudhakar R., "High Resistivity Zinc Stannate As A Buffer Layer In CdS/CdTe Solar Cells" (2005). USF Tampa Graduate Theses and Dissertations.