High Resistivity Zinc Stannate As A Buffer Layer In CdS/CdTe Solar Cells

Author

Sudhakar R. Gayam, University of South Florida

Graduation Year

2005

Document Type

Thesis

Degree

M.S.E.E.

Degree Granting Department

Electrical Engineering

Major Professor

Christos S. Ferekides, Ph.D.

Committee Member

Don L. Morel, Ph.D.

Committee Member

Yun L. Chiou, Ph.D.

Keywords

Semiconductors, Thin films, Transparent conducting materials, Sputtering, Interdiffusion

Abstract

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 V_OC = 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.
https://digitalcommons.usf.edu/etd/2893