Dramatic Recrystallization During CdCl2 Treatment of Evaporated CdTe Thin Filmsa

In this work, we report the different effects of CdCl₂ treatment on CdTe films deposited by thermal evaporation onto CdS and MgZnO (MZO) buffer layers. The main finding, which is relevant for understanding recent advances in CdTe device efficiency, is that few-μm thick CdTe films deposited on MZO can be induced to completely recrystallize forming a film consisting of grains that span the film thickness and are up to 30 μm laterally. On CdS buffer layers, the changes in microstructure with Cl treatment are much less pronounced and the final microstructure is less ideal for thin film photovoltaics. We propose a thermodynamic framework for understanding the microstructural changes during CdCl₂ treatment which can assist in understanding the wide range of behaviors observed across the many CdTe thin film solar cell fabrication procedures.