Effect of selenium and chlorine co-passivation in polycrystalline CdSeTe devices

CdTe-based solar cell efficiency has rapidly improved over the last few years. Some of the reasons have been a change to the absorber composition including the incorporation of selenium, and better front contact and emitter materials in CdTe photovoltaic devices. In addition to the increase in short-circuit current by reducing the bandgap, Se plays other important roles in passivation of defects thus improving the conversion efficiency of CdSeTe/CdTe graded absorber photovoltaic devices. Here, we combine structural and optical characterizations with first principles calculations to investigate the role of Se and Cl segregation in CdSeTe devices. We find that in the presence of Se and Cl, the minority carrier lifetime improves due to a reduction of midgap defect states. We also correlate this effect with defect passivation in CdSeTe devices and suggest innovative ways to further improve CdTe-based photovoltaic efficiency.