Low Surface Recombination Velocity by Low-Absorption Silicon Nitride on c-Si

We demonstrate that nearly stoichiometric amorphous silicon nitride (SiN x) 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 SiN x 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 S_eff,UL of 1.6 cm/s on 0.85-Ω·cm p -type and immeasurably low S_eff,UL on 0.47-Ω·cm n-type silicon passivated by the SiN x deposited at 290°C. Capacitance-voltage (C-V) measurements reveal that 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 S_eff,UL with calculated S_eff,UL by an extended Shockley-Read-Hall (SRH) model, we conclude that either Defect A or B (or both) observed by Schmidt is likely to dominate the surface recombination at our Si-SiNx interface. In addition to the outstanding surface passivation, this SiN x has a low absorption coefficient at short wavelengths. Compared with Si-rich SiNx of an equivalent passivation, the optimized SiN x would enhance the photogenerated current density by more than 0.66 mA/cm²or 1.40 mA/cm² for solar cells encapsulated in glass/ethylene-vinyl acetate 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.