Research and development of CdS/CdTe solar cells incorporating ZnTe layers.
This thesis presents experimental work and analysis in research and development of low-cost thin film solar cells. In this work, three semiconducting materials were studied. These semiconducting materials are from group II-VI or also known as 'two-sixers' from periodic table. The semiconductors are cadmium sulfide (CdS), cadmium telluride (CdTe) and zinc telluride (ZnTe).All of these layers were obtained by growing them using electrodeposition in aqueous solutions. In this project, electrodeposition using 2-electrode system was employed to deposit all of the semiconductors. The decision was taken to avoid contamination that might be happening due to the leakage of foreign ions such as K+ and Ag+ contained in the reference electrode into the electrolyte.To help in optimizing the semiconducting layers, three characterization techniques were used frequently. These techniques are optical absorption, x-ray diffraction (XRD) and photoelectrochemical (PEC) cell measurements. These techniques were used to study the optical, structural and electrical conductivity type of the electrodeposited layers respectively. After optimizing the layers using the above three techniques (optical absorption, XRD and PEC), other advance analytical techniques (SEM, XRF, D.C. conductivity measurement, photoluminescence and UPS) were used to fully characterize the materials. This information was also used to further optimize the material layers. At the later stage of this project, research was concentrated on fabricating and assessing solar cell devices. Initial devices fabricated had glass/FTO/CdS/CdTe/Au structure. Current-voltage (I-V) measurement was employed to assess the performance of solar cell devices by measuring the open circuit voltage (V[oc]), short circuit current density (J[sc]), fill factor (FF) and conversion efficiency (eta). The highest efficiency obtained from this solar cell structure was 10.1%. However, this structure had low fill factors in the range of 0.25 to 0.4.To solve this problem, an insulating layer was incorporated into the device to create metal-insulator-semiconductor type structures. Results have shown that by electrodepositing insulating p-type ZnTe layers on top of CdTe, the fill factor can be improved.
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Sheffield Hallam University (United Kingdom).