Passivation of Boron-Doped Industrial Silicon Emitters by Thermal Atomic Layer Deposited Titanium Oxide

Abstract

Passivation of p + -doped silicon is demonstrated by using water (H 2 O)-based thermal atomic layer-deposited titanium oxide (TiO x ) films. Emitter saturation current density (J 0 e ) values below 30 fA/cm 2 are obtained on textured p + -doped samples with a sheet resistance in the 80-120 Ω/sq range. This low emitter saturation current density would allow open-circuit voltages up to 720 mV when this TiO x film is used in n-type silicon wafer solar cells with a front boron emitter. In addition, the optical properties of TiO x make it an excellent option for use as antireflection coating on the silicon wafer solar cell after encapsulation. Thus, the results demonstrated in this paper could enable interesting new routes for future high-efficiency n-type silicon wafer solar cells.

Local Structure of High Performance TiOx Electron‐Selective Contact Revealed by Electron Energy Loss Spectroscopy

“…Among them, ALD‐TiO x thin layers have been intensely investigated since it functions as a good passivation layer for c‐Si surface due to the low deposition damage to c‐Si surface and the ability to fabricate sub 5 nm thick films. Indeed, it is well known that the good passivation performance is provided by the ALD‐TiO x /c‐Si heterocontact after postannealing at about 300 °C . We reported that the origin of improved passivation by postannealing is effusion of hydrogen and hydrogenated molecules from H‐terminated c‐Si and subsequent formation of a silicon oxide (SiO x ) layer at the TiO x /c‐Si interface .…”

“…This implies that chemical passivation is responsible for the increased τ eff , since the almost identical maximum τ eff value of 1521 µs is observed regardless of the polarity of minority charge carrier. Therefore, the passivation scheme of the TiO x /SiO x stacks on c‐Si is not attributed to field‐effect passivation originating from the presence of fixed charge but chemical passivation originating from the termination of interfacial dangling bonds …”

Evidence for Chemicals Intermingling at Silicon/Titanium Oxide (TiOx) Interface and Existence of Multiple Bonding States in Monolithic TiOx

“…In recent years, the search continued to find novel dielectrics with multifunctional capabilities in order to further alleviate the surface recombination, enhance the efficiency, and reduce the cost of c‐Si solar cells. Titanium oxide (TiO x ) is one such emerging dielectric for c‐Si solar cells due to its excellent optical properties, remarkable carrier selectivity, and excellent surface passivation features . Liao et al and Gad et al have previously demonstrated that atomic layer deposited (ALD) TiO x is able to provide excellent surface passivation on c‐Si surfaces, in addition to its ideal optical properties (refractive index of ≈2.4 at a wavelength of 632.8 nm and a relatively low absorption in the visible wavelength range) to be used as an antireflection coating (ARC) for encapsulated silicon wafer solar cells.…”

“…Titanium oxide (TiO x ) is one such emerging dielectric for c‐Si solar cells due to its excellent optical properties, remarkable carrier selectivity, and excellent surface passivation features . Liao et al and Gad et al have previously demonstrated that atomic layer deposited (ALD) TiO x is able to provide excellent surface passivation on c‐Si surfaces, in addition to its ideal optical properties (refractive index of ≈2.4 at a wavelength of 632.8 nm and a relatively low absorption in the visible wavelength range) to be used as an antireflection coating (ARC) for encapsulated silicon wafer solar cells. Yang et al have suggested that smart carrier selective contacts not only provide excellent surface passivation but also allow the efficient transport of one type of carrier (electrons or holes).…”

Smooth anti-reflective three-dimensional textures for liquid phase crystallized silicon thin-film solar cells on glass

“…section 3.4), which we estimate from a one-diode model to about Δ , ≈ 3 . Therefore, the increased Voc of silicon thin-film solar cells on SMART superstrates might be attributed to passivation properties of the TiOx layer, which are already known from literature [27][28][29][30]. However, further investigations are needed in order to elucidate this hypothesis, e.g.…”