Comparison of POCl3 diffusion and phosphorus ion-implantation induced gettering in crystalline Si solar cells

Abstract

Most p-type Si solar cells involves phosphorus-doped emitter by POCl 3 diffusion or phosphorus ionimplantation. Although the formation of the phosphorus emitter is known to getter impurities like Fe, the difference in the impact of these two gettering techniques on cell performance is not well quantified. Therefore, this paper compares the gettering efficiency of POCl 3 diffusion and phosphorus ionimplantation on Czochralski(Cz) and cast quasi-mono Si wafers. Cz-Si wafers were used to measure bulk lifetime and iron concentration before and after POCl 3 diffusion and phosphorus implantation with different doses. Increase in phosphorus implantation dose improved the gettering efficiency by increasing bulk lifetime and decreasing iron concentration but remained inferior to POCl 3 diffusion partly due to single side gettering as opposed to double side gettering with higher phosphorus surface concentration during POCl 3 diffusion. Moreover, large-area solar cells were fabricated on cast quasi-mono and Cz-Si wafers to quantify the impact of these emitters on cell parameters. POCl 3 diffused cast quasi-mono cells showed ~0.4% higher efficiency due to higher bulk lifetime compared to phosphorus implanted emitter. However, phosphorus implanted Cz cells gave ~0.3% higher efficiency due to lower emitter saturation current, resulting from the benefit of in-situ oxide surface passivation during the implant anneal.

Impact of Standard Cleaning on Electrical and Optical Properties of Phosphorus-Doped Black Silicon

“…Lastly, we note that unintended etching of highly phosphorusdoped planar and nanotextured silicon can significantly impact theoretical studies seeking to elucidate the impact of different emitter profiles on solar cell performance [36], [37], or, for example, impurity gettering [38]- [42]. Unnecessary cleaning between emitter realization and emitter characterization should therefore be minimized and any HF dips and SC1 cleanings should be carefully reported in such future studies.…”

Hole-selective molybdenum oxide as a full-area rear contact to crystalline p-type Si solar cells

“…Further details on front surface process can be found elsewhere. [21][22][23] The front grid contacts were formed by standard photolithography and e-beam evaporation of Ti=Pd=Ag (10=10=1000 nm), followed by lift-off, and then thickened by electroplating of Ag. The front contact sintering step was performed at 400 °C for 10 min in forming gas ambient.…”

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

“…The art of gettering, the mitigation of deleterious trace impurities, has garnered attention throughout the history of photovoltaics. While this topic is thoroughly researched for phosphorus emitters operating under infinite-source diffusion, the topic of gettering with finite-source emitters is still in its infancy [1][2][3]. Finite-source emitters offer benefits, such as, better blue response and no phosphosilicate glass formation [3][4][5].…”