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https://ptsldigital.ukm.my/jspui/handle/123456789/519495| Title: | Development Of ZnxCd1-xS Window Layer For Cadmium Telluride (Cdte) Thin Film Solar Cells |
| Authors: | Md. Sharafat Hossain (P55861) |
| Supervisor: | Nowshad Amin, Professor Dr. |
| Keywords: | Development Of ZnxCd1-xS Window Layer Window Layer For Cadmium Telluride Cdte Thin Film Solar Cells Solar cells |
| Issue Date: | Jul-2013 |
| Description: | Poly-crystalline CdS has been found to be the suitable heterojunction partner for CdTe solar cell, however, the conventional polycrystalline CdS/CdTe cell has several drawbacks, such as CdS has low bandgap (2.42 eV), inter diffusion of lower bandgap (1.3 eV) CdS1-yTey material at the p-n junction, high lattice mismatch between CdTe and CdS that limit device performance. In order to overcome these problems, this research proposed the introduction of ZnxCd1-xS as window layer in CdTe solar cells. A novel method has been introduced to control the composition of ZnxCd1-xS window material to be applied in CdTe solar cells with optimum value of ��x��. The novelty is that ZnxCd1-xS thin films have been fabricated by RF magnetron co-sputtering using CdS and ZnS targets by varying the RF power ratios of CdS and ZnS to control the composition ��x��. The effects of the ZnxCd1-xS layer on CdTe solar cell performance have been studied through numerical simulation achieving highest efficiency 21.87% (Voc = 0.98 V, Jsc = 26.57 mA/cm2, FF = 0.84), experimental fabrication and characterizations. Numerical simulation is used to evaluate the effects of TCO front contacts (ITO/FTO), ZnxCd1-xS window materials and back surface field effects on the cell performance. The stress analysis of ZnxCd1-xS/CdTe solar cells for the effect of temperature was also performed. Strategies to improve efficiency and cell performance are explored from simulation works. Prospects of ultra-thin CdTe absorber layer is also modelled and it is found 1 μm thick absorber layer yields comparable conversion efficiency of 19.15% with the conventional CdTe solar cells with 4 μm thick absorber layer. In practical fabrication of ZnxCd1-xS window layers, sputtering parameters such as RF powers of CdS at 40 W and ZnS from 5-32 W (for optimizing the composition ��x��), substrate temperature (100-400 0C), operating pressure (8-20 mTorr), thickness of the films (50-300 nm), annealing temperature (200-500 0C) and time (5-30 min.) for optimum value of ��x��=0.2, were varied and the effects of structural and optical properties were evaluated to find the optimum sputtering parameters through various characterization tools. Experimentally, to fabricate an ultra-thin CdTe solar cell structure, CdTe layer of 1.1-4.5 μm were deposited on top of TCO/ZnxCd1-xS as the absorber layer aiming to attain reduced material and energy input. The cell was activated using CdCl2 heat treatment at 400 0C for 15 minutes. Different back surface field (BSF) materials have been investigated for best performance. RF sputtering and screen-printing have been used to deposit final back contacts on top of ITO or FTO/ZnxCd1-xS/CdTe/BSF stacks under various conditions during which the process has been optimized. Comparing all the results, it is seen that the structure of Glass/ITO/Zn0.2Cd0.8S/CdTe/Cu-doped C-paste/Ag Paste exhibits best cell efficiency of 8.97% with considerably high value of Voc (0.882 V) but low FF (0.67). The low FF may be attributed to the high resistivity of the junction between CdTe and back contact and the high resistivity of Zn0.2Cd0.8S window layer although low concentration of Zn is used and consequently outcomes poor FF. In conclusion, this study has investigated the potentials of ZnxCd1-xS window layers and opened up the usage for CdTe solar cells for better conversion efficiency as a result of theoretical and practical investigation.,PhD |
| Pages: | 198 |
| Call Number: | TK2960 .H655 2013 3 |
| Publisher: | UKM, Bangi |
| Appears in Collections: | Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina |
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