Characterizing TeO2 Formation in CdTe Devices Using Transmission Electron Microscopy

Poly-crystalline CdTe/Cd(Se)Te based thin film solar cells have shown to be competitive in terms of efficiency and cost of electricity production. Yet, the presence of hetero-interfaces in Cd(Se)Te structure and low minority carrier lifetime have limited the thin film devices from reaching their maximum theoretical efficiency of approximately 30 percent. The back-contact of CdSeTe devices has been identified as one significant limitation to increased device performance since no metal has been identified that has a sufficiently high work function to create an Ohmic contact with the CdTe absorber at the back-surface of the film stack. Here, we will explore the formation of native TeO
2
on the back contact of solar cells to draw inferences on device performance. Atomic-resolution imaging in a scanning transmission electron microscope (STEM) combined with electron energy-loss spectroscopy (EELS) are used to characterize these devices and to inform the production process. The goal is to identify the mechanisms of TeO
2
formation and its role in passivating the back contact.