Progress in Low-temperature Surface Passivation of Silicon Solar Cells using Remote-plasma Silicon Nitride

Abstract

Using a remote‐plasma technique as opposed to the conventional direct‐plasma technique, significant progress has been obtained at ISFH in the area of low‐temperature surface passivation of p‐type crystalline silicon solar cells by means of silicon nitride (SiN) films fabricated at 350–400°C in a plasma‐enhanced chemical vapour deposition system. If applied to the rear surface of the low‐resistivity p‐type substrates, the remote‐plasma SiN films provide outstanding surface recombination velocities (SRVs) as low as 4 cm s−1, which is by a clear margin the lowest value ever obtained on a low‐resistivity p‐Si wafer passivated by a solid film, including highest quality thermal oxides. Compared to direct‐plasma SiN films or thermally grown oxides, the remote‐plasma films not only provide significantly better SRVs on low‐resistivity p‐silicon wafers, but also an enormously improved stability against ultraviolet (UV) light. The potential of these remote‐plasma silicon nitride films for silicon solar cell applications is further increased by the fact that they provide a surface passivation on phosphorus‐diffused emitters which is comparable to high‐quality thermal oxides. Furthermore, if combined with a thermal oxide and a caesium treatment, the films induce a UV‐stable inversion‐layer emitter of outstanding electronic quality. Due to the low deposition temperature and the high refraction index, these remote‐plasma SiN films act as highly efficient surface‐passivating antireflection coatings. Application of these films to cost‐effective silicon solar cell designs presently under development at ISFH turned out to be most successful, as demonstrated by diffused p‐n junction cells with efficiencies above 19%, by bifacial p‐n junction cells with front and rear efficiencies above 18%, by mask‐free evaporated p‐n junction cells with efficiencies above 18% and by MIS inversion‐layer cells with a new record efficiency of above 17%. All cells are found to be stable during a UV test corresponding to more than 4 years of glass‐encapsulated outdoor operation. © 1997 John Wiley & Sons, Ltd.

High-efficiency Silicon Heterojunction Solar Cells: A Review

“…Wet-thermal oxides are grown at lower temperatures [10], and have proven their use in solar cells [11,12]. Other PV-suitable dielectrics include amorphous siliconnitride (a-SiN x :H) [13,14], SiO 2 /a-SiN x :H stacks [9,15], or aluminum-oxide (Al 2 O 3 / films [16][17][18]. As the frontside passivation layer is insulating, contacts to the emitter are made by "spiking" the metal (usually silver) to the emitter, making direct contact with the electronically active absorber [19][20][21].…”

Bulk and surface passivation of silicon solar cells accomplished by silicon nitride deposited on industrial scale by microwave PECVD

“…4,5 In the meantime tremendous progress has been achieved, both in the quality of the surface passivation that can be obtained and in understanding the physical mechanisms behind the phenomenon of surface passivation. [6][7][8][9][10][11][12][13][14][15][16] Now that surface passivation using silicon nitride can be made as good as that using a thermal oxide, the material is increasingly used for the fabrication of high-efficiency silicon solar cells. [17][18][19] Big advantages of silicon nitride grown by PECVD with respect to thermal oxide are the low process temperature (typically in the range 300-400 C) and the short process time (typically a few minutes).…”

Hydrogénation effect on low temperature internal gettering in multicrystalline silicon

“…Silicon nitride dielectric layers deposited by plasma-enhanced chemical vapour deposition (PECVD) are commonly used to passivate wafer surfaces in silicon solar cell production [25,26]. These films have a high hydrogen concentration [27,28].…”