The role of O2 in CdSeTe thin film deposition and CdSeTe/CdTe solar cell performance

By integrating CdSeTe alloy into CdTe based thin-film solar cells, high efficiency above 19% has been obtained. However, the role of O-2 during the CdSeTe deposition has not been studied since the current reported CdSeTe deposition process by close space sublimation (CSS) is free of oxygen. We found the oxygen performed an important role in this process. Here, we prepared CdSeTe films under O-2/N-2 ambient and apply them as absorblayer together with CdTe. The effects of O-2 on the CdSeTe deposition, material performance, and devices have been studied. Oxygen in the ambient can increase Se content in the CdSeTe alloy for the as-deposited films. A two-step reaction process of oxidation - sublimation is proposed to explain the role of oxygen. The oxygen facilitates the amount of Se content into the vapor then in the film. With the oxygen appearance, the composition of as-deposited CdSeTe films and the source can be controlled relative stable. This technique makes the process of depositing CdSeTe thin film by CSS for long time operation feasible. The short circuit current density (J(sc)) and fill factor (FF) of the cells are promoted with the introduce of oxygen. A process of high efficiency (Eff.) (>= 19%) CdSeTe/CdTe cells with oxygen in the CSS deposition is developed, which is repeatable and also compatible with both the existing manufacturing and laboratory CdTe process and equipment.