Revealing Surface and Interface Evolution of Molybdenum Nitride as Carrier-Selective Contacts for Crystalline Silicon Solar Cells

Molybdenum nitride (MoN_x) was perceived as carrier-selective contacts (CSCs) for crystalline silicon (c-Si) solar cells due to having proper work functions and excellent conductivities. However, the poor passivation and non-Ohmic contact at the c-Si/MoN_x interface endow an inferior hole selectivity. Here, the surface, interface, and bulk structures of MoN_x films are systematically investigated by X-ray scattering, surface spectroscopy, and electron microscope analysis to reveal the carrier-selective features. Surface layers with the composition of MoO_2.51N_0.21 form upon air exposure, which induces the overestimated work function and explains the origin of inferior hole selectivities. The c-Si/MoN_x interface is confirmed to adopt long-term stability, providing guidance for designing stable CSCs. A detailed evolution of the scattering length density, domain sizes, and crystallinity in the bulk phase is presented to elucidate its superior conductivity. These multiscale structural investigations offer a clear structure-function correlation of MoN_x films, providing key inspiration for developing excellent CSCs for c-Si solar cells.