Finite- vs. infinite-source emitters in silicon photovoltaics: Effect on transition metal gettering

Abstract

Control of detrimental metal impurities is crucial to silicon solar cell performance. Traditional silicon solar cell emitters are diffused in an infinite-source regime and are known to cause strong point defect segregation towards the emitter and thus enhance bulk minority carrier diffusion length. With the advent of ion-implantation and chemical vapor deposition (CVD) glasses, finite-source diffused emitters are attracting interest. This contribution aims to increase their adoption by elucidating the dominant gettering mechanisms present in finite-source diffused emitters. Our findings indicate that infinite-source diffusion is critical for effective segregation gettering, but that high enough surface phosphorus concentration can activate segregation gettering via finite-source diffusion as well. In the case of ionimplanted emitters, the traditional segregation gettering may be considerably enhanced by impurity precipitation in the implanted layer.

Dissociation and Formation Kinetics of Iron–Boron Pairs in Silicon after Phosphorus Implantation Gettering

“…the active phosphorus concentration in the emitter surface [P + ]surf and its sheet resistance Rsh, were found to be affected by the anneal temperature. Note that a similar effect is previously reported by Laine et al [10]. The investigation of FeB dissociation kinetics was carried out according to two standard illumination intensities: 1 sun and 0.5 sun by using of a solar simulator setup.…”

“…The oxygen concentration in these wafers is around 10.50 ppma. The Fe-contamination of the wafers was carried out by immersing them in an iron-spiked RCA solution [10]. The iron was diffused into the bulk at 850 °C during an extended period of 50 minutes, in order to ensure a uniform Fe contamination of the bulk with an interstitial iron concentration [Fei]0 = 1.8 × 10 13 cm -3 .…”

Cu gettering by phosphorus-doped emitters in p-type silicon: Effect on light-induced degradation

“…Electrochemical Capacitance-Voltage (ECV) measurements performed on similarly processed wafers also indicated a peak electrically active phosphorus concentration of ∼2 × 10 20 cm 3 and a junction depth of ∼0.4 µm. 20 Next, the processing of all wafers continued with the intentional Cu contamination. This step was executed by thinning the backside oxide layer down to 45±10 nm in buffered HF and subsequently depositing droplets of a 15 ppb% (w/v) Cu sulfate solution on a small area (∼10-11 cm 2 ) of the oxidized backside.…”

The gettering effect of dielectric films for silicon solar cells

“…Phosphorus diffusion gettering is commonly applied to remove unwanted impurities in silicon, and the gettering process is conveniently coupled with the formation of n+ regions near the silicon wafer surfaces. Effective gettering via phosphorus diffusion, however, relies on the full-area high-temperature heavy diffusion processes, with lighter diffusions or ion implanted phosphorus regions being much less effective at gettering [1][2][3][4]. Moreover, novel high efficiency cell architectures, for instance, heterojunction and passivating contact solar cells, no longer require heavy phosphorus or boron diffusion to form p-n junctions.…”