Magnesium Fluoride Electron-Selective Contacts for Crystalline Silicon Solar Cells

In this study, we present a novel application of thin magnesium fluoride films to form electron–selective contacts to <i>n</i>-type crystalline silicon (c-Si). This allows the demonstration of a 20.1%-efficient c-Si solar cell. The electron-selective contact is composed of deposited layers of amorphous silicon (∼6.5 nm), magnesium fluoride (∼1 nm), and aluminum (∼300 nm). X-ray photoelectron spectroscopy reveals a work function of 3.5 eV at the MgF₂/Al interface, significantly lower than that of aluminum itself (∼4.2 eV), enabling an Ohmic contact between the aluminum electrode and <i>n</i>-type c-Si. The optimized contact structure exhibits a contact resistivity of ∼76 mΩ·cm², sufficiently low for a full-area contact to solar cells, together with a very low contact recombination current density of ∼10 fA/cm². We demonstrate that electrodes functionalized with thin magnesium fluoride films significantly improve the performance of silicon solar cells. The novel contacts can potentially be implemented also in organic optoelectronic devices, including photovoltaics, thin film transistors, or light emitting diodes

Hydrogen-Assisted Defect Engineering of Doped Poly-Si Films for Passivating Contact Solar Cells

Hydrogen-assisted defect engineering, via a hydrogenated silicon nitride (SiNx:H) capping layer, on doped polycrystalline silicon (poly-Si) passivating-contact structures, is explored using complementary techniques. The hydrogen treatment universally improves the passivation quality of poly-Si/SiOx stacks on all samples investigated. Meanwhile, their contact resistivity remains very low at ∼6 mΩ·cm2. Moreover, the nature of charge carrier recombination within the poly-Si films is also investigated by means of photoluminescence. On planar c-Si substrates, the poly-Si films emit two broad photoluminescence peaks at ∼850–1050 and ∼1300–1500 nm. The former is the characteristic peak of the hydrogenated amorphous Si (a-Si:H) phase and only appears after the treatment, demonstrating that (i) a significant amount of hydrogen has been driven into the poly-Si film and (ii) an amorphous phase is present within it. The second peak originates from sub-band-gap radiative defects inside the poly-Si films and increases after the treatment, suggesting a suppression of their nonradiative recombination channels. For films deposited on textured c-Si substrates, there is a disrupted oxide boundary, preventing a buildup of excess carriers inside the films and leading to quenching of the film luminescence