Industrial tunnel oxide and passivated contact (i-TOPCon) solar cells were metallized at Fraunhofer ISE using ultrashort pulse laser ablation of the passivation layers for the subsequent Ni/Cu/Ag plating process. The solar cells feature a tunnel SiOx and n-type doped polysilicon layer covered by a SiNx at the rear side, whereas the front side is made of a boron emitter passivated with a AlOx/SiNx stack. The reference i-TOPCon solar cells screen-printed at the supplier reach an efficiency of 23.46% measured by Fraunhofer ISE CalLab. The impact of the laser process on the implied open circuit voltage (iV(oc)) is characterized showing minor impact on the TOPCon side, while the emitter side reveals an increased iV(oc) loss due to laser damage. Loss analysis by simulating the plated solar cells points out the benefit of reducing the laser contact opening (LCO) area in terms of shading and contact recombination. Optimization of laser ablation and hydrofluoric acid (HF) pretreatment process result in V-oc > 700 mV and FF > 82% leading to a mean efficiency 23.6% measured in-house and a champion efficiency of 23.84% measured at Fraunhofer ISE CalLab thus outperforming the references by 0.4%(abs).

Plated Ni/Cu/Ag contacts offer the possibility to significantly reduce silver consumption for tunnel oxide passivated contact (TOPCon) solar cells. This work demonstrates industrial bifacial TOPCon solar cells with plated Ni/Cu/Ag metallization achieving champion solar cell efficiencies of up to 24.0%. The influence of reduced poly-Si thickness down to 60 nm of the TOPCon rear side on the open circuit voltage (V-oc) is analysed and the impact of laser-induced damage during laser contact opening (LCO) is characterized. Furthermore, mitigation strategies to systematic fill factor losses are developed including laser-induced nano-roughness within the LCO to increase contact adhesion and current-annealing to improve contact resistance.

This work investigates in detail plating of Ni/Cu/Ag contacts as an alternative metallization approach for industrial bifacial tunneling oxide and passivating contacts (i-TOPCon) silicon solar cells. We have achieved a 23.3 % champion cell efficiency on a front and rear plated bifacial TOPCon silicon solar cell on industrial precursors on a 9 busbar design reaching the same mean efficiency level (eta = 23.0 %) as industrially processed identical screen printed references. Further, plating metallization demonstrates the potential to contact poly-Si layer thicknesses below 100 inn with reasonable J(0,met). The substitution of printed silver by plated copper leads to a significant reduction in the cost of ownership of the metallization backend for i-TOPCon solar cells of about 7.38 $ct/wafer. The integration of plated Ni/Cu/Ag contacts enables a reduction in Ag consumption of about 19.7 t/Gigawatt production capacity compared to screen printing metallization.

Three approaches to close the efficiency gap between screen-printed Ag-paste and Ni/Cu/Ag-plated front contact metallization on industrial passivated emitter and rear cells (PERC) solar cells are presented in this paper. In the first approach, the POCl3 diffusion is adjusted to an emitter profile (reduced peak doping) for plated contacts. The second approach is to adapt the laser over doping (LOD) process of the phosphor silicate glass (PSG) to create the selective emitter to the properties of laser patterning and plating. In the third approach, we vary the process step order of front laser patterning and back side aluminum firing. The three approaches show very promising results. Efficiencies higher than 22% and open-circuit voltage V-OC values of close to 680 mV are reached on a cell area of 251,99cm(2). Overall the values excel the reference values obtained with screen printing and firing of Ag-paste. For future developments, V-OC values between 685 mV and 690 mV and efficiencies around 22.5% seem very likely.

In this work, we highlight the benefits of alternative plating routes compared to the standard plating route primarily discussed in literature and currently introduced in pilot production [1, 2]. The common plating route starts with the laser ablation of the front side grid after rear side Al-printing and firing. Then, an HF dip removes the native oxide for the subsequent light induced nickel-, copper plating (LIP) with a silver capping as a finishing. Afterwards, an annealing step improves the adhesion of the plated grid and its contact resistance. Here, we want to show the advantage of three alternative process routes. In the first alternative route, the laser opening of the front side grid is performed before the firing step. During firing, the laser damage is partly cured and can lead to an increase in open circuit voltage (Voc) of 7 mV on state of the art industrial PERC solar cells. For the second process route, the removal of the native oxide is eliminated. To achieve this, special laser and plating conditions are needed. Finally, for the third alternative process route, the annealing of the plated stack can be combined with a stabilization process suppressing the light induced degradation (LID). The presented alternative routes give new degrees of freedom for process optimizations regarding precursor-induced features such as high laser damage on shallow emitters, parasitic plating (PP) for passivation layers with high pinhole density or LID.

To help photovoltaic energy gain a larger share in the world’s total energy mix it is essential to further reduce the cost of solar generated energy and in parallel to enable mass production at a scale 100-1000 times higher than today. Plated metal contacts may play an essential role to produce industrial c-Si solar cells and modules with higher output power at reduced cost per Wattpeak. The technology enables manufacturing reliable metal contacts with excellent adhesion when pull-testing on conventionally soldered interconnection ribbons and is also adequate for thin wafers. An average efficiency of 19.6% is reported for industrial p-type Al-BSF CZ-Si solar cells with light induced plated Ni/Cu contacts formed after laser ablation. IEC61215 testing on modules fabricated from these solar cells is in progress. For PERC/PERL-type Si solar cells a peak efficiency of 20.83% has been independently confirmed by FhG-ISE CalLab. Cu plating technology allows for significantly reduced consumable cost while paving the way towards higher c-Si solar cell and module performance in industrial mass production. A key technology for sustainable PV growth is introduced and positively evaluated in an economic assessment.

Replacing Ag paste contacts in silicon solar cells by plated Ni/Cu contacts seems a logical next step in the evolution of industrial Si solar cell manufacturing. Ag paste contacts cause a significant share of the solar cell cost today and limit the efficiency of advanced Si solar cells. However, replacing a proven technology by another requires reliability of this technology. Cost and efficiency advantages alone are a high motivation for adopting a new metallization technology in mass production. Reliability of the contacts is a must. In this contribution we show that laser ablation followed by light induced plating of Ni and Cu and plating of a thin capping layer results in good and reliable contacts on industrial solar cell precursors. After plating of the complete metal stack a thermal annealing step is used to increase mechanical adhesion and to reduce resistive losses of the plated contacts (contact resistance and grid resistance). Excellent solar cell efficiencies can be combined with reliable contacts. Adhesion data and data after 60 cell module testing (as part of IEC61215) are reported next to the most influencing factors.

This paper describes a viable path for the mass production of Si solar cells that lead to lower cost for PV electrical energy. Systems and modules having solar cells with plated metal contacts benefit from both, a higher solar cell performance as well as significantly reduced consumable cost. As most advances in industrial solar cell production over the past decades the introduction of plating technology benefits from significant equipment and material improvements. In parallel this road offers to shift the limits with respect to achievable solar cell efficiency by inherent advantages such as the possibility to form narrower metal contacts of excellent conductivity at low cost and the possibility to contact moderately doped Si areas. Efficiency improvements depend on the degree that other processing steps are adapted to the new degree of freedom in optimization offered by plated contact formation. Efficiency improvement is experimentally demonstrated. Equipment solutions and cost aspects are addressed. Besides good reliability and adhesion of the plated contacts we show efficiency potential exceeding 21% for PERC-type Si solar cells.