As the global demand for clean energy accelerates, solar cell manufacturers are under pressure to improve device efficiency, reduce fabrication costs, and make manufacturing processes more sustainable. Achieving these goals simultaneously presents complex challenges, especially as need intensifies and production volumes scale. The push to realize innovative solutions stems from the need to overcome bottlenecks in both design and fabrication. One major obstacle is that efficiency gains from conventional silicon photovoltaic cell architectures, such as passivated emitter and rear contact (PERC), are beginning to plateau. At the same time, the rising costs of materials plagues existing photovoltaic designs. Tunnel oxide passivated contact (TOPCon) technology is a promising solution that has rapidly gained a foothold among solar cell manufacturers. This technology offers performance improvements compared to alternative approaches through more effective passivation and carrier collection. To realize the full promise and poten-tial of TOPCon technology, however, industry must overcome several barriers. Fundamentally, TOPCon technology requires advanced processing techniques, especially in metallization. Notably, traditional screen printing of silver, which is the current mainstay of photovoltaic contact formation, is increasingly incompatible with the fine-feature structures, cost targets, and overall growth and sustainability potential of the TOPCon architecture. To chart a path forward, manufacturers are turning to the method of laser contact opening (LCO) combined with electrochemical metal plating of copper. Here, the use of ultrashort-pulse (USP) UV lasers to selectively ablate dielectric layers is a key enabler, delivering precise and efficient copper-based metallization. The use of USP UV lasers is a natural choice for a delicate material removal process such as that which takes place during LCO. USP lasers are highly effective for ablating material with high spatial precision and minimal thermal diffusion. The objective of LCO — to remove dielectric layers without significantly affecting the underlying silicon and silicon dioxide layers (which could impair performance) — is a suitable task for these sources. As this approach gains momentum, manufacturers and instrument developers are optimizing process parameters to achieve maximum levels of performance, efficiency, and cost effectiveness. Their aim is to streamline a methodology that offers a scalable solution that aligns with the solar industry’s evolving performance, sustainability, and economic goals. LCO and electrochemical plating solution Screen printing with silver paste is well established as the standard process for forming metal contacts in crystalline silicon solar cells. But the limitations of this process are becoming more pronounced, especially for advanced cell architectures such as TOPCon. One facet of the problem is purely economic. According to The Silver Institute’s World Silver Survey 2025, photovoltaic solar cell production consumes ~17% of the world’s annual silver supply. As the price of silver increases — it has doubled during the past decade — so does the cost to produce solar cells. The TOPCon architecture uses up to 50% more silver than other designs, including the PERC type that TOPCon is replacing1. There are also technical limitations. Silver paste metallization restricts solar cell design because it produces wider, taller conductive “fingers.” These cause optical shading and resistive losses, which ultimately serve to degrade cell efficiency. Even the screen-printing process itself, which involves physical contact and high-temperature firing, can cause problems: It can stress or damage sensitive thin films or the wafers themselves. The combination of LCO with electrochemical plating (LCO + plating) offers an attractive alternative, especially for the rear side of advanced cells, such as TOPCon. In this process, USP UV lasers are used to ablate micron-scale openings in the dielectric stack that protects, passivates, and adds function to the silicon photovoltaic wafer. These openings are subsequently metallized through electrochemical plating with nickel, copper, and a capping layer of tin or silver (Figure 1). This approach to metallization can yield finer lines, reduce shadowing, and improve current collection. Additionally, switching to copper reduces material costs and mitigates the reliance on a more limited and precious natural resource. Figure 1. The two-step laser contact opening (LCO) and plating process. Silicon nitride (SiNx) and polycrystalline silicon (n+ poly Si) layers are typically 100 nm or thinner, and the silicon dioxide (SiO2) tunnel oxide is ~2 nm or less. Additional layers of nickel (Ni), copper (Cu), and tin (Sn) are shown. Courtesy of MKS/Spectra-Physics. Although the LCO + plating method introduces greater manufacturing complexity, with the use of new processes and equipment it ultimately promises performance gains, scalability, and reduced operating costs over time. LCO process considerations In a series of tests, MKS/Spectra-Physics application engineers sought to more effectively characterize the process optimization necessary for the successful adoption of LCO + plating. The tests balanced essential process metrics, including quality, throughput, yields, and cost. The performance of the completed devices was also characterized to gauge the overall efficiency that can be expected of solar cells fabricated using LCO + plating. The results highlight the effect of various laser parameters on the process. As it relates to the use of USP UV, it is important to consider that the antireflection and passivation layers that comprise current solar cells typically consist of silicon nitride and silicon oxide. Because the silicon nitride layer is relatively transparent to UV light, the laser energy is mostly absorbed by the underlying silicon. This material is heated until it ejects the overlying dielectric through plasma formation and rapid localized heating. While this indirect mechanism allows the upper layer to be removed without excessive thermal loading, it also introduces its own challenges. Specifically, the interaction depth must be tuned very precisely. Insufficient energy produces incomplete ablation, while too much energy can breach the thin ( Experimental results One core question that the MKS/Spectra-Physics team attempted to answer was which class of USP laser — picosecond or femtosecond — delivered the best results (Figure 2). For most processes, picosecond lasers offer higher material removal rates while still balancing quality. But, in thin-film applications such as TOPCon LCO, femtosecond lasers can deliver both higher throughput and better quality. This is because of their lower ablation threshold and shallower confinement of the irradiating energy. Figure 2. Light microscope images showing three examples of LCOs processed with both types of ultrashort-pulse (USP) lasers, including picosecond quasi-flattop (left) and Gaussian (center) distributions, and femtosecond Gaussian intensity distributions (right). Courtesy of MKS/Spectra-Physics. The influence of beam profile was also explored. A quasi-flattop intensity distribution was compared to the traditional Gaussian distribution to determine whether one allowed better control over ablation depth and uniformity. Surprisingly, in many tests, less material was removed at the beam center than at its edges. This is contrary to typical results with Gaussian beam ablation, where the higher center intensity typically causes more material removal. A possible explanation is that the laser intensity at the beam edge is not sufficient to initiate nonlinear absorption in the overlying layer. As a result, more energy simply passes through that layer and penetrates the silicon, causing ablation. In the heat-affected zone region, absorption causes extremely rapid heating and subsequent cooling, causing amorphization of the p+ polycrystalline silicon (Figure 3). Converting this material back into a polycrystalline form requires an additional melting/recrystallization cycle, which is typically performed using a furnace firing process. Figure 3. The area ablated by three overlapping picosecond laser pulses is shown. It is classified into four distinct regions: an inner ablative zone, an outer ablative zone, a heat-affected zone, and an unaffected zone. Material removal does not occur in the heat-affected zone, but changes — such as melting and/or amorphization — are evident in this process step. Courtesy of MKS/Spectra-Physics. Discussion The results represent just a small sample of all the tests performed. But, the full set of results yielded some conclusions. First, a picosecond-pulse UV laser is likely to be the best choice for TOPCon LCO processing. It can be optimized to deliver cell efficiency results equivalent to standard screen-printed metallization — and it is more cost-effective than a femtosecond-pulse UV laser. Also, while the femtosecond laser can theoretically offer a slight throughput advantage, it may fail to do so in practice due to challenges in the beam delivery system. Both types of USP lasers offer sufficiently high pulse energies and average powers, and the beam delivery approach will largely define the overall system throughput. This approach is likely to include multiple high-speed scanning stations, beamsplitting optics, and, possibly, other components. However, cell architectures are rapidly evolving and becoming more complex; it is possible that future hybrid architectures may benefit from femtosecond pulses. Such an architecture could be, for example, TOPCon technology integrated with interdigitated back contacts. Simply, as structures become more complex, and layers grow thinner, the potential need for femtosecond pulses increases. Additionally, such structures also stand to benefit from the self-aligning nature of plating metallization. The engineering team also concluded from the tests that simple Gaussian beam focusing provides the required layer selectivity for successful LCO processing. While the quasi-flattop provides less unwanted ablation at the beam edge, the larger LCO features that result are detrimental to the overall performance of a finished TOPCon cell. Plating metallization Following LCO processing, additional steps and processes must be taken to realize effective plating. The next critical step is metallization, since it significantly influences the electrical performance, long-term stability, and overall cost of the device. In this context, plating-based metallization is attracting significant interest as a more sustainable and scalable alternative to screen printing with silver pastes. Plating typically involves depositing a sequence of metals. It begins most often with nickel, to form the ohmic contact and serve as a barrier to copper diffusion. Next, a thicker copper layer is placed, which functions to carry the bulk of the current. Finally, a capping layer, such as tin or silver, is added to enhance solderability and deter corrosion. The two main plating techniques in use today are electroless and electrochemical deposition. Electroless plating offers certain benefits for fragile wafers, such as the possibility of double-sided processing without the need for physical contact. Electrochemical deposition, on the other hand, provides faster deposition rates and higher material purity. While it typically requires more complex handling and equipment, electrochemical deposition is also the more established of the two techniques. Yet regardless of the method, success in plating hinges on the quality and consistency of the laser openings. Precise, well-defined laser openings ensure uniform metal coverage, low-contact resistance, and robust mechanical adhesion. These factors are essential for high-efficiency, commercially viable solar cells. Cell performance measurements The performance potential of the LCO + plating approach has been demonstrated in both laboratory and pilot-scale environments. One key study, performed in collaboration with the Fraunhofer Institute for Solar Energy Systems ISE (Fraunhofer ISE), was conducted on TOPCon devices using MKS/Spectra-Physics laser systems and plating chemistries from MKS/Atotech. The wafer precursors used in this study were optimized for screen-printed metallization, not LCO, but the plating was performed with high-quality, lab-grade tools. The Fraunhofer ISE group measured efficiencies of up to 23.3% for these cells. It also showed open-circuit voltages of ~693 mV and fill factors >82%. This is comparable to the results (24% efficiency) obtained using screen-printed metallization. Testing by other groups, which simultaneously optimized all elements of the process — including wafer structure, laser parameters, and plating chemistry — reported efficiencies as high as 26.7%. This value is near the upper bound and considered to be achievable for manufacturable TOPCon cells. Future insights As the solar industry shifts toward higher-efficiency architectures such as TOPCon, the limitations of traditional silver screen printing are becoming increasingly prominent. LCO combined with copper-based plating offers a compelling alternative: This approach supports fine-feature metallization, reduces material costs, and aligns with long-term industry sustainability goals (Figure 4). While successful implementation requires careful coordination between the laser processing and metallization steps, test results indicate that the approach can achieve high efficiency and scalability. Figure 4. A focused ion beam cross-section analysis of an electrochemical deposition (ECD) plated contact shows favorable contact among the metal layers and polycrystalline silicon (n+ poly Si) substrate film. USP UV lasers enable the transition from expensive, screen-printed silver contacts to electrochemically plated copper, reducing cost and improving solar cell performance. Courtesy of MKS/Spectra-Physics. As process integration continues to mature, LCO plating is poised to play a key role in enabling the next generation of cost-effective, high-performance photovoltaic technologies. Reference 1. Verband Deutscher Maschinen- und Anlagenbau (VDMA) 2025. International Technology Roadmap for Photovoltaics (ITRPV) report 2025, www.vdma.eu/en-gb/international-technology-roadmap-photovoltaic.