Fabrication And Characterization Of Thin Film On Polyethylene Terephthalate Substrate For Cigs Solar Cell

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Date
2012-04
Authors
Faraj, Mohammad Ghaffar
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Publisher
Universiti Sains Malaysia
Abstract
The cost of the electrical energy generated by the solar cells was higher than that generated by fossil fuels. Cost reduction of the solar cell is therefore required. Feasibility of fabricating thin film CIGS solar cells on low-cost polyethylene terephthalate (PET) substrates in order to bring down the costs of the CIGS solar cell technology was explored. The structure CIGS solar cells consisted of polyethylene terephthalate (PET) substrate, molybdenum back contact reflector, CIGS absorber layer, cadmium sulfide (CdS) buffer layer and zinc oxide (ZnO) window layer have been evaluated. The Mo back contact layer, with a thickness of 800 nm, was deposited on a PET substrate using direct current (DC) sputtering. The AFM surface study showed that the surface of the Mo films was also smooth, presenting an RMS of 25.09 nm. The resistivity of the films deposited was 1.6 × 10-5 Ω.cm. A 1.5 μm thick p-type CIGS with a Ga content that varied from 0.3-0.6 were deposited using a screen-printing technique. The RMS surface roughness of the CIGS film varied from 71.35-33.95 nm for Ga contents (0.3-0.6), and the band-gap energies of the CIGS thin films increased with an increasing Ga/(In + Ga) ratio. From the electrical properties, it was found that CIGS films with different Ga ratios always show p-type conductivity. A CdS thin film with a thickness of 100 nm was deposited using a thermal evaporation technique. It was found that the RMS for the CdS thin film was 3.46 nm, and the transmission rate was more than 60% for wavelengths longer than 500 nm. The band gap for the CdS thin film was 2.41eV. The as-deposited CdS thin film had a high resistivity of 923Ω.cm.These results show that the CdS thin film has properties that make them ideal as a buffer layer in CIGS solar cells. The ZnO window layer with a thickness of 300 nm was studied using a thermal evaporation technique. It was found that the RMS for the ZnO thin film was 16.23 nm, and the band gap for the ZnO thin film was 3.375 eV. The as-deposited ZnO thin film had a resistivity of 12×10-4 Ω.cm. These results show the ZnO thin film has properties that make them ideal as a window layer in CIGS solar cells.
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Keywords
Feasibility of fabricating thin film CIGS solar cells , on low-cost polyethylene terephthalate
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