High Lifetime Ga‐Doped Cz‐Si for Carrier‐Selective Junction Solar Cells

Abstract

Industrial mass production of solar cells is at a transition toward carrier‐selective junction solar cells with passivating contacts such as TOPCon, POLO, or heterojunction technology (HJT). At the same time, many manufacturers consider switching from p‐type Cz‐Si to n‐type Cz‐Si wafers. This contribution indicates that Ga‐doped p‐type Cz‐Si material is still a viable option for the new type of devices while giving an opportunity to benefit from lower wafer cost. The minority carrier diffusion lengths that are an order of magnitude larger than the thickness of the studied HJT and TOPCoRE devices are reported. Stability aspects for operation in the field are discussed. Best TOPCoRE solar cells on Ga‐doped Cz‐Si show a 0.2% higher efficiency than their co‐processed n‐type counterparts.

Investigating Wafer Quality in Industrial Czochralski‐Grown Gallium‐Doped p‐Type Silicon Ingots with Melt Recharging

“…This again suggests that some impurities may be accumulating in the residual melt after each ingot growth, and are then partly incorporated in subsequent ingots. We note that the effective lifetimes reported here are significantly lower than those reported by Horzel et al, [ 7 ] for example. This is due to the significantly lower resistivity of the wafers used in this study, which is representative of typical industrial Ga‐doped p‐type PERC cells.…”

“…Based on the known diffusivity of Fe i in silicon, we would expect a FeGa pair association time constant τ assoc of 799 s, from the expression, τ assoc ¼ 5.0 Â 10 5 T N A exp 0.66 kT À Á , where T is temperature and N A is dopant concentration. [18] The very good agreement between this value and the measured time constant is strong evidence that the changes in the effective lifetimes after light soaking are indeed caused by the formation of FeGa pairs, as opposed to other possible light-induced degradation (LID) such as light and elevated temperature-induced degradation (LeTID) [3,4,6,7] or copper-related LID [20] Figure 4b shows the estimated [Fe i ] as a function of solidified fraction in the three RCz-Si ingots. Note, we used a range of injection levels (6 Â 10 14 -6 Â 10 15 cm À3 ) instead of a single injection level to help estimate the uncertainties in [Fe i ].…”

“…\frac{0.66}{k T} \left.\right)$ , where T is temperature and is dopant concentration. [ 18 ] The very good agreement between this value and the measured time constant is strong evidence that the changes in the effective lifetimes after light soaking are indeed caused by the formation of FeGa pairs, as opposed to other possible light‐induced degradation (LID) such as light and elevated temperature‐induced degradation (LeTID) [ 3,4,6,7 ] or copper‐related LID [ 20 ]…”

“…The silicon photovoltaic (PV) industry has recently moved away from boron (B) and transitioned to gallium (Ga) as the main dopant element for p-type Czochralski-grown silicon (Cz-Si) wafers, primarily to avoid the well-known boron-oxygen defect. [1,2] Although several articles have reported higher effective minority carrier lifetimes in Ga-doped wafers than in B-doped wafers, [3][4][5][6][7] detailed studies of the material quality of industrial Ga-doped ingots are still rather limited. Recently, Horzel et al [7] reported effective lifetimes in the range of 3-17 ms along a customgrown Ga-doped Cz ingot with a resistivity range of 5-12 Ω cm.…”

“…[1,2] Although several articles have reported higher effective minority carrier lifetimes in Ga-doped wafers than in B-doped wafers, [3][4][5][6][7] detailed studies of the material quality of industrial Ga-doped ingots are still rather limited. Recently, Horzel et al [7] reported effective lifetimes in the range of 3-17 ms along a customgrown Ga-doped Cz ingot with a resistivity range of 5-12 Ω cm. However, studies of effective lifetimes along standard ingots with resistivities below 1 Ω cm, as is typical for industrial Ga-doped passivated emitter and rear cells (PERC) are necessary to assess the quality of ingots used in mass production.…”