In CdTe-based devices the "back-contact" is a crucial subject of scientific and industrial importance, since it affects the conversion efficiency and the long-term stability of solar cells. It is common to Te-enriched CdTe surface by chemical etching. Here it is proposed a new way for obtaining a CdTe film with a Te-rich surface taking advantage of the original treatment in Chlorine atmosphere, alternative to the use of CdCl2, without doing any CdTe etching. The back-contact formation on this Te-rich surface occurs by using a buffer layer, which indifferently could be Sb2Te3, As2Te3 or Bi2Te3, deposited by sputtering or by evaporation at low temperature (≈ 200 °C), followed by the deposition of a metal contact (Mo). In this condition, I-V characteristic of the solar cell shows the typical roll-over behavior, distinctive of a rectifying back-contact. Performing an annealing of the device, at a temperature of 200 °C, in air for a few minutes, the roll-over disappears and the fill factor increases considerably. If the annealing is not made in air, or in presence of Oxygen, the roll-over doesn't disappear. Preliminary accelerated ageing tests have shown a good contact stability of these CdTe solar cells. We will explain why the CdTe surface is Te-rich only after an annealing in air at 200 °C and how this can contribute to form an ohmic and stable back-contact in presence of Sb-, As- and Bi-based chalcogenide.

KEY DEVELOPMENTS IN CdTe THIN FILM SOLAR CELL BACK-CONTACT

ROMEO, Alessandro;RIMMAUDO, Ivan;SALAVEI, Andrei
2013-01-01

Abstract

In CdTe-based devices the "back-contact" is a crucial subject of scientific and industrial importance, since it affects the conversion efficiency and the long-term stability of solar cells. It is common to Te-enriched CdTe surface by chemical etching. Here it is proposed a new way for obtaining a CdTe film with a Te-rich surface taking advantage of the original treatment in Chlorine atmosphere, alternative to the use of CdCl2, without doing any CdTe etching. The back-contact formation on this Te-rich surface occurs by using a buffer layer, which indifferently could be Sb2Te3, As2Te3 or Bi2Te3, deposited by sputtering or by evaporation at low temperature (≈ 200 °C), followed by the deposition of a metal contact (Mo). In this condition, I-V characteristic of the solar cell shows the typical roll-over behavior, distinctive of a rectifying back-contact. Performing an annealing of the device, at a temperature of 200 °C, in air for a few minutes, the roll-over disappears and the fill factor increases considerably. If the annealing is not made in air, or in presence of Oxygen, the roll-over doesn't disappear. Preliminary accelerated ageing tests have shown a good contact stability of these CdTe solar cells. We will explain why the CdTe surface is Te-rich only after an annealing in air at 200 °C and how this can contribute to form an ohmic and stable back-contact in presence of Sb-, As- and Bi-based chalcogenide.
2013
3936338337
CdTe; Solar Cells; back contact
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11562/646952
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