In the past, we described a dry process for the fabrication of CdTe/CdS thin film solar cells. In this process, most ofthe layers composing the cell, namely ITO, ZnO, CdS and back contact are deposited by sputtering and CdTe isdeposited by close-spaced sublimation. The treatment of CdTe is done at 400°C, for 10-20 minutes, without CdCl2,by using a Freon gas, dichlorofluoromethane, as a Cl supplier. Back contact is made by depositing onto a not-etchedCdTe film surface a buffer layer of As2Te3, followed by a thin layer of Cu and Mo. Recently, we modified the Cltreatmentand we improved the quality of the back contact. Since dichlorofluoromethane is an ozone depleting agentand its use is now forbidden, we replaced it with a gas, like Ar, containing 4%HCl and mixing it with a Fluorinecontaininggas, such as CHF3. Both these gases are not depleting agents and they aren’t forbidden. By adjusting therelative amounts of the chemical species into this mixture, we got results which are very similar to those obtainedwith dichlorofluoromethane. Concerning the back contact, we discovered that, by using as a buffer layer As2Te3, orBi2Te3 and by making an annealing in air at 200°C for 15-30 minutes, a stable and ohmic contact, without anyrollover in the solar cell I-V characteristic, is obtained.
Last Progress in CdTe/CdS Thin Film Solar Cell Fabrication Process
Menossi, Daniele;ROMEO, Alessandro;
2014-01-01
Abstract
In the past, we described a dry process for the fabrication of CdTe/CdS thin film solar cells. In this process, most ofthe layers composing the cell, namely ITO, ZnO, CdS and back contact are deposited by sputtering and CdTe isdeposited by close-spaced sublimation. The treatment of CdTe is done at 400°C, for 10-20 minutes, without CdCl2,by using a Freon gas, dichlorofluoromethane, as a Cl supplier. Back contact is made by depositing onto a not-etchedCdTe film surface a buffer layer of As2Te3, followed by a thin layer of Cu and Mo. Recently, we modified the Cltreatmentand we improved the quality of the back contact. Since dichlorofluoromethane is an ozone depleting agentand its use is now forbidden, we replaced it with a gas, like Ar, containing 4%HCl and mixing it with a Fluorinecontaininggas, such as CHF3. Both these gases are not depleting agents and they aren’t forbidden. By adjusting therelative amounts of the chemical species into this mixture, we got results which are very similar to those obtainedwith dichlorofluoromethane. Concerning the back contact, we discovered that, by using as a buffer layer As2Te3, orBi2Te3 and by making an annealing in air at 200°C for 15-30 minutes, a stable and ohmic contact, without anyrollover in the solar cell I-V characteristic, is obtained.
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