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 S-eff, UL of 1.6 cm/s on 0.85-Omega.cm p-type and immeasurably low Seff, UL on 0.47-Omega.cm n-type silicon passivated by the SiNx deposited at 290 degrees C. Capacitance-voltage (C - V) measurements reveal that this SiNx has a density of interface states of 3.0 x 10(11) eV(-1) cm(-2) at midgap and an insulator charge of 5.6 x 10(11) 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 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 with Si-rich SiNx of an equivalent passivation, the optimized SiNx would enhance the photogenerated current density by more than 0.66 mA/cm(2) or 1.40 mA/cm(2) 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.