In Situ Transmission Electron Microscopy: A Powerful Tool for the Characterization of Carrier-Selective Contacts

Abstract

In this study, a molybdenum oxide (MoOx) and aluminum (Al) contact structure for crystalline silicon (c-Si) solar cells was investigated using a combination of transmission line measurements (TLM) and in-situ transmission electron microscopy (TEM). Cross-sectional high-resolution TEM (HRTEM) micrographs revealed a ≈2 nm silicon oxide (SiOx) interlayer at c-Si/MoOx interface in the as-deposited state, indicating that formation of SiOx occurs during deposition of MoOx. Moreover, oxygen diffusion takes place from MoOx towards Al resulting in the formation of a ≈2-3 nm aluminum oxide (AlOx) interlayer at the MoOx/ Al interface. Based on the TLM measurements, the MoOx/Al contact structure retains ohmic transport with low contact resistivity up to 200°C and can therefore be a potential candidate for hole-selective rear contacts in a p-type c-Si solar cell. This work further demonstrates the value of in situ TEM for studying the thermal stability of transition metal oxide-based carrier selective contacts employed in high efficiency c-Si solar cells.