Low surface recombination velocity by low-absorption silicon nitride on c-Si

We demonstrate that nearly stoichiometric amorphous silicon nitride (SiNx) can exhibit excellent surface passivation on both p- and n-type c-Si as well as low absorption at short wavelengths. The key process to obtain such a SiNx is the optimized deposition pressure. The effective carrier lifetimes of these samples exceed the commonly accepted intrinsic upper limit over a wide range of excess carrier densities. We achieve a low Seff,UL of 1.6 cm/s on 0.85-Ω·cm p-type and immeasurably low Seff,UL on 0.47-Ω·cm n-type silicon passivated by the SiNx deposited at 290 °C. Capacitance-voltage measurements reveal this SiNx has a density of interface states of 3.0 × 10¹¹ eV⁻¹cm⁻² at midgap and an insulator charge of 5.6 × 10¹¹ cm⁻². By comparing the measured injection-dependent Seff,UL to calculated Seff,UL by an extended Shockley-Read-Hall model, we conclude that either Defect A or B (or both) observed by Schmidt et al. is likely to dominate the surface recombination at our Si-SiNx interface. In addition to the outstanding surface passivation, this SiNx has a low absorption coefficient at short wavelengths. Compared to Si-rich SiNx of an equivalent passivation, the optimized SiNx would enhance the photo-generated current density by more than 0.66 mA/cm² or 1.40 mA/cm² for solar cells encapsulated in glass/EVA or operating in air, respectively. The SiNx described here is ideally suited for high-efficiency solar cells, which require good surface passivation and low absorption from their front surface coatings.