Revealing the Importance of Front Interface Quality in Highly Doped CdSexTe1-x Solar Cells

As carrier concentration improves in CdTe-based solar cells, modeling shows that the front interface becomes a bottleneck for performance. Optimization of the front interface has proven difficult, however, because it both is buried and evolves substantially during standard superstrate device processing. Here, we address both issues by cleaving state-of-the-art superstrate CdSexTe1-x device stacks at the emitter/absorber interface and reconstructing in the substrate configuration using a MgyZn1-yO/ZnO:Al front contact. By comparing devices that were either copper- or arsenic-doped, the influence of front interface quality on low-doped and highly doped absorbers was studied, respectively. A much larger performance drop was observed for reconstructed arsenic-doped devices, which was attributed to insufficient emitter doping, formation of compensating defects at the front interface, and increased sensitivity to both effects due to a collapsed depletion region. This work highlights key challenges unique to highly doped CdSeTe:As devices that must be addressed moving forward.