In situ imaging of stacking fault removal during annealing of a CdTe solar cell

Stacking faults are ubiquitous in the CdTe photovoltaic absorber material. Although not detrimental to solar cell performance by themselves, they originate at grain boundary defect sites that act as charge traps, and stacking fault occurrence is thus indicative of the latter. Annealing in the presence of a Cl source is an established method for passivating these grain boundary defects and, in the process, removing stacking faults. The posttreatment of the absorber layer improves the solar power conversion efficiency by more than 300%. We propose to study the removal of stacking faults in situ during annealing by dark-field X-ray microscopy. The aim is to quantify the impact of Cl bonding at stacking fault-initiating defects at the grain boundaries on the kinetics of stacking fault removal. This will enable us to improve existing models of Cl activation, thereby enabling more efficient pathways for the passivation of grain boundary defects and, thus, more efficient CdTe solar cells.