SiNx and AlOx Nanolayers in Hole Selective Passivating Contacts for High Efficiency Silicon Solar Cells

The recombination of photogenerated charge carriers at metal-semiconductor interfaces remains a major source of efficiency loss in photovoltaic cells. Here, we present SiNx and AlOx nanolayers as promising interface dielectrics to enable high efficiency hole selective passivating contacts. It is demonstrated that SiNx deposited via direct plasma enhanced chemical vapour deposition can be grown controllably at thicknesses of 2 nm. The valence band offsets between crystalline silicon and ultrathin AlOx and SiNx nanolayers are measured as 3.5 and 1.4 eV, respectively. This predicts a larger tunnelling current for holes, compared to SiOx used typically. Resistivity measurements show that SiNx and AlOx nanolayers have lower contact resistivities compared to SiOx, with values as low as 100 m omega center dot cm(2). Analysis of the current transport mechanisms confirmed that tunnelling dominates the conduction through SiNx, while a mixture of tunnelling and pinholes are present in the AlOx structure. Lifetime measurements gave initial indications of the passivation quality of the films, with just 10 cycles of AlOx achieving 260 mu s after annealing and 1.9 ms with extrinsic field effect passivation added. Finally, the intrinsic built-in charge in the dielectrics was determined using surface photovoltage measurements and simulations are used to estimate the influence of nanolayer built-in charge in both poly-Si and dopant-free passivating contacts to enable future high efficiency solar cells.