The ZnO-reflectance effect on the heterojunction ITO/ZnO/CdS/CdTe

• Published in: 2012 38th IEEE Photovoltaic Specialists Conference pp. 002021 - 002023
• Main Authors: Pena, J. L., Rejon, V., Ares, O., Camacho, J. M., Rios-Flores, A.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.06.2012
• Subjects: antireflection coating; CdS; CdTe; Glass; Indium tin oxide; Optical films; Photovoltaic cells; Reflectivity; refractive index; Zinc oxide; ZnO
• ISBN: 1467300640; 9781467300643
• ISSN: 0160-8371
• DOI: 10.1109/PVSC.2012.6317995

The reported structure in this work was fabricated using layers ITO/ZnO/CdS/CdTe grown onto borosilicate commercial glass. The thin films of ITO and CdS were deposited using rf-sputtering in argon atmosphere from ITO and CdS targets. The ZnO layer also was deposited by rf-sputtering from metallic Zn target. All targets were of 5N of purity. The CdTe film was about 8 μm of thickness, was deposited onto CdS using a conventional closed space sublimation technique. By using basic calculus for optical antireflective coatings, was demonstrated that film ZnO has the nearest refraction index as needing for optical matching for ITO and CdS layers. The reflectance of the structure glass/ITO/ZnO/CdS/CdTe when the ZnO thickness is varied from 100-400 nm it is reported. In this work also the reflectance of the intermediate structures such as glass/ITO, glass/ITO/ZnO and glass/ITO/ZnO/CdS are reported. We found a minimum reflectance of 9% of the complete structure between 500-850 nm of wavelength. By taking the optimal thickness, a solar cell was fabricated, was activated by using CHClF 2 gas mixed with Ar at 400 °C for 5 minutes. As a back contact 15 nm of Cu and 500 nm of Mo were deposited by rf-sputtering in Ar atmosphere. The efficiency was about 10.1% for a cell of 1.01 cm2. After two months, the solar cell preserves its characteristics.