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We evaluate a procedure that is meant to ensure a highly accurate alignment between laser-doped lines and either screen-printed metal contacts or laser contact openings (LCO) for subsequent galvanic plating of the metal contacts. For both process routes, we prove that the application of the procedure significantly increases the alignment accuracy, discusses potential error sources, and identifies the major challenges for avoiding misalignment. As shown by the presented experiments, the use of screen-printed contacts is challenging for the alignment, since the laser doping process ""needs to foresee"" the screen print. For plated contacts, however, a much more accurate alignment can be achieved, since the LCO process ""can react"" on the previously applied laser-doped pattern. As we demonstrate, we are able to combine 10-mm-wide LCO lines with 36-mm-wide laser-doped lines (while ensuring that the passivation layer is only opened within the laser-doped area).

Investigating modifications of the silicon/metal interface during the manufacturing process and the influence on properties of laser-structured Ni-Cu-plated contacts enabled optimizing the metallization process. The micro pattern induced by ultrashort pulsed lasers ensures adhesion even without nickel silicide formation. Minimizing growth of laser-induced and native oxide at the surface of the laser patterned contact openings before plating enables high fill-factors without HF -treatment before metal deposition. Skipping the wet-chemical treatment eliminates parasitic plating on precursors with defective ARC. Compared to the state-of-the-art plating sequence, the approach presented features less process steps and enables improved solar cell aesthetics.

Laser ablation processes provide a potentially low cost and fast technology for microstructuring semiconductors, metals, or dielectrics. This paper deals with picosecond laser ablation ( $\lambda = 532\,{\text{nm}}$ , $\tau \approx 9\,{\rm{ps}}$ ) of III–V semiconductors. In particular, the external threshold fluence of thermal ablation is determined for InP, GaAs, and GaP. Furthermore, the applicability of laser ablation to the electrical separation of III–V solar cells is discussed. In this context, current–voltage characteristics are presented comparing GaInP single-junction solar cells separated by picosecond laser ablation and wet-chemical mesa etching. The laser process leads to a significant drop in open-circuit voltage and fill factor which is explained by a more than three times larger (unpassivated) surface area.

Plated silicon solar cells with nonoptimized antireflective coatings (ARCs) may feature parasitic plating (PP), i.e., unwanted metal depositions in ARC defects/pinholes. The present work introduces the easy plating sequence that takes advantage of native oxide growth to avoid plating in unwanted ARC pinholes or defects due to the electrical insulation of these defects. This prevents PP for plated solar cells. Independent of the ARC pinhole density, an aesthetic immaculate appearance can be achieved using easy plating. It is shown that it is possible to gain up to 0.5 mA/cm2 in short-circuit current density and 6 mV in open-circuit voltage compared to the reference plating sequence at Fraunhofer ISE. The importance to avoid drawbacks in terms of contact resistance and contact adhesion due to laser-induced or native oxide at the Si–Ni interface in the easy plating sequence is discussed in detail and important influencing factors in the process chain are lined out. At this stage of development, low contact resistances are possible in some cases but further research is necessary to fully understand the impact of solar cell design and process-related influencing factors. Easy plating can be an option to avoid PP independent of prior ARC pinhole density.

The state-of-the-art low-ohmic electrical contacting of highly boron-doped silicon surfaces is based on the use of screen-printed and fired silver-aluminum (Ag-Al) contacts. For these contacts, metal crystallites with depths of up to a few microns are observed at the interface. For screen-printed and fired Ag contacts on phosphorus-doped surfaces, the observed crystallite depths are much smaller. In this work, low-ohmic electrical contacting of local laser-doped p-type silicon surfaces with commercial pure Ag screen-printing paste are demonstrated. The doping layer is based on the "pPassDop" approach, which serves as a passivation layer on the rear side of p-type silicon solar cells. The specific contact resistances are measured down to 1 mu ohmb cm2 for p-type doping densities of about 3Ã1019cm-3 at the silicon surface and finger widths of around 55 mu m. Microstructure analysis reveals the formation of numerous small Ag crystallites at the interface with penetration depths o f less than 80nm. A first implementation of the "pPassDop" approach on 6-inch p-type Cz-Si bifacial solar cells using solely Ag contacts on both sides results in a peak front side energy conversion efficiency of 19.1%, measured on a black chuck with contact bars on both sides.

In this study we assess the reproducibility of the honeycomb texturing process, and we compare experimental values to a simulation. Our results show that the honeycomb-texture can be simulated with the OPAL program. It calculates the losses of any angle of incidence, where the short computation time is achieved by decoupling the ray tracing from the Fresnel equation. We investigate various surface morphologies and their impact on reflection values. The samples were etched at different etching times, whereby the honeycomb geometries were changed. Using our optimal acid etching solution ratio, we are able to fabricate a HC-texture with a reflectivity of R = 19.4 % (ω = 85°). Between the simulation values and those of the measurement, we see a difference of R = 0.3 % abs . This small deviation causes the relatively inaccuracies of the simulation and the measured samples. The focus is to simulate the different honeycomb structures and compare the values with the experimental values.

In emitter wrap through (EWT) solar cells, laser drilling is used to increase the light sensitive area by removing emitter contacts from the front side of the cell. For a cell area of 156 x 156 mm 2 , about 24000 via-holes with a diameter of 60 μm have to be drilled into silicon wafers with a thickness of 200 μm. The processing time of 10 to 20 s is determined by the number of laser pulses required for safely opening every hole on the bottom side. Therefore, the largest wafer thickness occurring in a production line defines the processing time. However, wafer thickness varies by roughly ±20 %. To reduce the processing time, a coaxial camera control system was integrated into the laser scanner. It observes the bottom breakthrough from the front side of the wafer by measuring the process emissions of every single laser pulse. To achieve the frame rates and latency times required by the repetition rate of the laser (10 kHz), a camera based on cellular neural networks (CNN) was used where the images are processed directly on the camera chip by 176 x 144 sensor–processor–elements. One image per laser pulse is processed within 36 μs corresponding to a maximum pulse rate of 25 kHz. The laser is stopped when all of the holes are open on the bottom side. The result is a quality control system in which the processing time of a production line is defined by average instead of maximum wafer thickness.

27th European Photovoltaic Solar Energy Conference and Exhibition; 828-831, The HIP-MWT (High Performance Metal Wrap Through) cell is a simplified variant of the metal wrap through passivated emitter and rear cell (MWT-PERC). In this paper, the transferability of this concept from lab scale to pilot line processing is presented. The suitability of the cell concept for integration in newly developed back contact modules is tested and demonstrated. Based on results from lab-scale production, the HIP-MWT fabrication process is improved. Moreover, options for further process accelerations and cost reduction are identified. Finally the solar cell to module compatibility is investigated and simple portable solutions for back contact cell interconnection and adaptions of the cell’s anti-reflective coating are presented.