| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Energy Harvesting & Storage | Tuesday Sessions |
| Session EH-TuM |
| Session: | Solar Cells |
| Presenter: | Juan Peña, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico |
| Authors: | L. Peña, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico V. Rejón, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico M. Riech, Universidad Autónoma de Yucatán, Mexico N. Hernández-Rodríguez, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico |
| Correspondent: | Click to Email |
Today CdS/CdTe heterojunction is an important photovoltaic system for conversion of solar energy. Due to the simple techniques used for thin films deposition, it has been brought from laboratory to industrial scale. Although the thin films are deposited by using techniques such as sputtering and CSS, the back contact layers are a challenge in both: the formation of an ohmic contact and that endures a long time. There are several prospects for back contacts using Mo as can be seen in [1]. The solar cell with Cu/Mo as a back contact deposited by using rf-sputtering is reported in [2]. There are few researches that studied how Mo film can be protected against oxidation without adding series resistance. The bilayer Mo/ITO has been used in microelectronics devices [3].
In this work, the CdS/CdTe solar cells that uses Cu/Mo as back contact is investigated. It is shown that the formation of MoOx at surface of Mo thin film influences the series resistance. The oxide is formed when the solar cell is used at outdoor conditions without any encapsulation. Here some indoor experiments were made. First, we show how the Mo/Glass film is oxidized when it is annealed at 400 °C in air. Second, how the Mo is degraded at same conditions when it is used on CdTe/CdS cell and annealed at same conditions. Third, how ITO works when it is deposited over of Mo on the solar cell. Preliminary results indicates that the ITO avoids the formation of MoOx and mechanical scratching , preserves its electrical properties and the solar cell shows good stability after an annealing at 400 °C.
The films Cu, Mo and ITO were deposited by rf-sputtering. We show evidences that the p-n junction remains working properly and the oxidation of Mo is the main cause of the cell efficiency degradation. By using the thin film of ITO on Mo layer all solar cell characteristics are preserved. The CdTe film was grown by conventional CSS technique. The cells were activated by using CHClF2-argon-oxygen gases. DRX spectra and HR-SEM were made for Mo/Glass and ITO/Mo/CdTe structure before and after annealing at 400 °C in air.
Acknowledgement
This work has been supported by CONACYT-México under contract FORDECYT-116157, FOMIX-169739 and FOMIX-172298, CeMIE-Sol PY-207450/25. Measurements were performed at LANNBIO CINVESTAV-Mérida, under support from projects FOMIX-Yucatán 2008-108160, CONACYT LAB-2009-01 No. 123913 and CB2012/ 178947.
References
[1] D. L. Batzner, et al. Thin Solid Films, vol. 451-452, pp. 536-543, 2004.
[2] V. Rejón, et al. Solar Energy, vol. 95, pp. 319-324, 2013.
[3] H. Piao, et al. Surface and Interface Analysis, vol. 39, pp. 493-500, 2007.