Sublimation of Mg onto CdS/CdTe films fabricated by advanced deposition system

One way to improve the efficiency of CdS/CdTe solar cells is to incorporate complex CdTe alloys into the device architecture. While formation of wider bandgap Cd_1-xMg_xTe has been demonstrated with sputtering and co-evaporation, use of sublimation techniques for large areas is yet to be investigated. Using a sublimation technique suitable for large area processing, we deposited Mg thin films onto TEC10 and TEC10/CdS/CdTe structures. XPS depth profiling and ellipsometry show that the Mg and the underlying CdTe layer intermixed substantially, formed an alloyed film, and incorporated oxides into the film. For non-CdCl₂ treated CdS/CdTe devices coated with Mg, a 120 mV gain in V_oc was realized by utilizing a Br₂/methanol etching process prior to metallization. Nonetheless, additional measures are needed to effectively implement this complex alloy into a high efficiency device structure. Use of statistical process optimization and high vacuum systems are suggested to improve the film quality.