Graduation Year

2003

Document Type

Thesis

Degree

M.S.E.E.

Degree Granting Department

Electrical Engineering

Major Professor

S.Ferekides, Dr.Christos

Keywords

czt, widegap semiconductors, sublimation, tandem solar cells, thin films

Abstract

Currently thin film solar cells have efficiencies in the range of 16-18%. Higher efficiencies of 20% or more can be achieved by two junction solar cells in which two p-n junctions are connected in series one on top of the other in a tandem structure. The ideal bandgaps for optimum efficiency in a tandem structure are about 1eV for the top cell and 1.7 eV for the bottom cell. Copper Indium Gallium di-Selenide (CIGS) with a bandgap of 1 eV is a suitable candidate for the bottom cell and Cadmium Zinc Telluride (CZT) with a tunable bandgap of 1.44-2.26 eV is a suitable candidate for the top cell. This work involves characterization of cadmium zinc telluride films and solar cells prepared by close spaced sublimation. CZT is deposited by co-sublimation of CdTe and ZnTe. The process has been investigated on various wide bandgap semiconductor materials including cadmium sulphide, cadmium oxide and zinc selenide.

Different post deposition heat treatments were carried out to determine their effect on film and device properties. Characterization of the CZT devices was done using XRD, EDS, SIMS, J-V and spectral response measurements. CZT (Eg~1.7 eV) /CdS exhibited best performance when compared to the other window layers investigated. The best device exhibited Voc=640mV, FF=40% and Jsc=4.5 mA/cm2. The theoretical performance of CZT based solar cells were investigated using SCAPS. The effect of bulk and interface defects on the device parameters were studied.

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