Understanding the Copassivation Effect of Cl and Se for CdTe Grain Boundaries

Chlorine passivation treatment of cadmium telluride (CdTe) solar cells improves device performance by assisting electron–hole carrier separation at CdTe grain boundaries. Further improvement in efficiency is observed after alloying the absorber layer with selenium. High-resolution secondary ion mass spectroscopy (NanoSIMS) imaging has been used to determine distribution selenium and chlorine boundaries a selenium-graded device. Atomistic modeling based on density functional theory (DFT-1/2) further reveals that presence an exemplar (110)/(100) boundary passivates critical acceptor defects leads n-type inversion boundary. The defect state analysis provides explanation for band-bending effects energy band alignment results, thereby elucidating mechanisms high efficiencies Se-alloyed Cl-passivated cells.