Characterizing the Back-Contact Interface of Poly-Crystalline Cd(Se)Te Devices Using Transmission Electron Microscopy

Poly-crystalline 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.[1] The back-contact of CdSeTe devices is a significant limitation to increased device performance since no metal has been identified that has a sufficiently high work function for Ohmic contact with the CdTe absorber at the back-surface of the film stack. Thin layers of different materials are tried for band-engineering to achieve passivation and hole-selectivity.[2] Here, we will explore novel back-contact film layers in an effort to overcome this energy band mismatch. Atomic-resolution imaging in a scanning transmission electron microscope (STEM) combined with electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (XEDS) are used to characterize these devices and to inform the production process. The goal is to identify the ideal atomic and electronic structures, as well as any interfacial diffusion of elements.