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Abstract: In this paper the tradeoff between process control and cost-effectiveness for PERL-type process flows is investigated. Three aspects are considered: (1) whether a surface pre-treatment (for example special cleans and/or oxidation) prior to the deposition of the Al2O3-based rear-side passivation stack has to be added to the flow; (2) the quantification of the impact on cell parameters of skipping the rear-side polishing and/or the Al2O3 deposition; and (3) the possibility of replacing Al paste with PVD Al for rear side metallization. It is found that: (1) SPM-like cleans or thermal oxidation prior to Al2O3 deposition are useful steps to guarantee a stable Al2O3-based passivation process. (2) The efficiency drops by more than 1% by skipping the polishing, but only ≈0.15% by removing the Al2O3 from the passivation stack. Therefore, while rear-side polishing appears to be a necessary step for PERC/PERL technologies, the insertion of Al2O3 in the passivation stack could be traded off for a reduced production cost, depending on the (company-specific) details of cost-calculations. (3) Replacing Al paste with PVD Al for rear side metallization results in a deteriorated reflectance. The effect is larger for thinner passivation stacks. Although less advantageous in term of material costs with respect to PVD Al, screen-printed Al would therefore be the preferred choice for PERL cells featuring thin passivation stacks. [Copyright &y& Elsevier]

Poly-Si/SiO x passivating contacts enable the manufacturing of highly-efficient Si solar cells, but their fabrication commonly relies on an extra high-temperature process such as dopant diffusion or thermal annealing for achieving excellent passivation and contacting properties. This extra process is eliminated in the fired passivating contact (FPC) approach used for simplified fabrication of poly-Si/SiO x passivating contacts. Instead, FPCs rely on the thermal budget of the fast/short and high-temperature firing process used for metallization of solar cells to achieve similar final properties. Despite this, compatibility of FPCs with industrially viable metallization techniques has not been demonstrated yet, which is studied in this work for fire-through Ag screen-printing and Ni/Ag plating. With screen-printing, low recombination current density (J 0) down to 4.9 fA/cm2, low contact resistivity between the Ag contacts and the FPC (ρ c,m) down to 7.2 mΩ⋅cm2, and Ohmic transport through the FPC including the SiO x film were achieved using wet-chemically grown SiO x. Nevertheless, J 0 of metallized regions (J 0,m) exceeded 1000 fA/cm2. Reducing J 0,m was attempted by mitigating the blistering observed in FPCs, but J 0,m remained high. With Ni/Ag plating, excellent surface passivation with J 0 down to 2.7 fA/cm2 and very low J 0,m < 50 fA/cm2 were achieved, but no Ohmic contacts could be obtained. Integration of screen-printed FPCs in large-area n-TOPCon solar cells was also demonstrated, yielding average efficiencies of 18.4%, limited mainly by the high J 0,m and series resistance of the FPCs. The results presented reveal the challenges for the industrialization of FPCs and provide valuable insights for tackling these. [Display omitted] • Fired passivating contacts (FPCs) developed relying only on the thermal budget of firing and not on conventional annealing. • Compatibility of FPCs with fire-through Ag screen-printing and Ni/Ag plating tested. • Screen-printing: J 0,pass ≈ 5 fA/cm2 & ρ c < 10 mΩ∙cm2 achieved, but J 0,metal was high. • Plating: J 0,pass < 3 fA/cm2 & J 0,metal < 50 fA/cm2 achieved, but contacts were non-Ohmic. • Integration of FPCs in screen-printed large-area n-TOPCon cells led to 18.4% efficiency. [ABSTRACT FROM AUTHOR]

This work evaluates the potential of selective epitaxy to mitigate the recombination losses at the p-type contact regions of plated bifacial n-type PERT cells. Following the growth of a 500 nm, 2.5 1019 cm−3 boron doped epitaxial layer at the emitter contact regions defined by laser ablation of the passivating dielectrics, both an increase in V oc (+6 mV) and FF (+1% absolute) are measured in the final cells compared to the reference with a homogeneous diffused emitter. These results come with an average efficiency gain of 0.3 and 0.5% absolute for front and rear side illumination, respectively. If the diffused, blanket emitter in the passivated regions is replaced by a thicker, lowly doped epitaxial profile (3 μm, 5 1018 cm−3) to further reduce recombination, an additional rise in implied V oc after metallization of 10 mV is estimated. This increase would be the result of a reduction in J 0,pass, emitter (down to 6 fA/cm2) and J 0,plated, emitter (down to 1967 fA/cm2). Image 1 • Selective growth of doped regions by epitaxy on laser ablated textured surfaces. • Metallization by simultaneous plating of n- and p-type contacts in bifacial cells. • Reduced J 0,plated for p-type contacts by doping profile engineering with epitaxy. • Thermal SiO 2 /PECVD SiN x passivation after epitaxy at the same level than ALD Al 2 O 3. • Gain in FF and V oc for bifacial cells with a selective epitaxial emitter approach. [ABSTRACT FROM AUTHOR]