Investigation Of The Thermal Stability Of Moox As Hole-Selective Contacts For Si Solar Cells

The stoichiometry and work function of molybdenum oxide (MoOx) are of crucial importance for its performance as hole selective contact for crystalline silicon solar cells. Hydrogenated amorphous silicon (a-Si:H) is typically used as an interface passivation layer in combination with MoOx to reduce surface recombination. As the fabrication process of a solar cell typically contains subsequent high-temperature processes, the consideration of thermal stability of MoOx with and without a-Si:H becomes critical. In this work, in situ x-ray spectroscopy (XPS)/ultraviolet photoelectron spectroscopy and Fourier transform infrared spectroscopy in the temperature range from 300 K to 900 K are used to investigate the thermal stability of MoOx with and without a-Si:H. In addition, both the passivation and contact performance are studied by evaluating the surface saturation current density J(0s), carrier lifetime tau(eff), and contact resistivity rho(c). The XPS results reveal that the as-evaporated MoOx on top of both c-Si and a-Si:H is sub-stoichiometric, and the work function of both films is higher than 6eV. While after in situ annealing, the evolution of MoOx phase on top of a-Si:H shows a different behavior compared to it on c-Si which is attributed to H diffusion from a-Si:H after 600 K, whereas the work function shows a similar trend as a function of the annealing temperature. The J(0s) of a p-type Si symmetrically passivated by MoOx is found to be 187 fA/cm(2) and the rho(c) is similar to 82.5 m Omega.cm(2) in the as-evaporated state. With a-Si interface passivation layer, J(0s) is significantly lower at 5.39 fA/cm(2). The J(0s) and the rho(c) increase after post-deposition annealing. The evolution of these functional properties can be attributed to the material properties. Published by AIP Publishing.