To cope with the worldwide increasing demand for photovoltaics, it is inevitable for solar cell metallization to switch from scarce silver to abundantly available copper. To this end, this work offers a silver-free and industrially feasible ultra-low-temperature metallization approach called mask and plate. Using this metallization scheme, which is mainly based on inkjet printing of a resist and galvanic metal deposition, pure copper metal electrodes are applied to industrial M6-sized (edge length of 166 mm) silicon heterojunction (SHJ) solar cells' front sides. While the screen-printed reference cells use (6 f 1) mg W- 1 of silver, the mask and plate pendants use (4 f 2) mg W- 1 of copper instead on busbarless half cells' front sides. Due to a width reduction of the electrodes down to (14 f 2) mu m and the electrodes' low lateral resistivity of (2.0 f 0.6) mu Omega cm, mask and plate outperforms screen printing regarding photoconversion efficiency by 0.6 %abs on average, while silver is completely substituted by copper. This work further demonstrates the applicability of mask and plate copper metallization to 1.21 cm2-sized perovskite silicon tandem solar cells without significant damage. It can, thus, be an enabler for silver-free industrial metallization of next-generation solar cells.

The top cell of a perovskite silicon tandem solar cell requires several material layers on each side of the perovskite absorber to efficiently extract electrons and holes, respectively. These layers must meet multiple requirements simultaneously, namely, low interface recombination, good charge carrier selectivity, low contact resistivity, and high optical transparency. Due to the complex architecture, characterization techniques are required in material and process optimization to identify loss mechanisms. Spatial resolution of the characterization is gaining importance along with the upscaling of the perovskite technology. Herein, electro‐ and photoluminescence (EL and PL) imaging is combined with illuminated lock‐in thermography (ILIT) for a comprehensive electro‐optical characterization of both subcells in perovskite silicon tandem devices with state‐of‐the‐art cell architecture. Thereby, the combination of the presented characterization methods together with numerical simulation models enables to carry out holistic investigations of device limitations. The strength of this approach is showcased by one particularly remarkable feature that is observed in the investigated tandem device, showing a low PL but high EL signal at local spots. Together with multidimensional optoelectrical device simulations, the measurements are explained and the root cause of this feature to originate from the perovskite/C 60 interface is suggested.

Electroplated copper electrodes are manufactured for the first time on 22.5 cm(2) two-terminal perovskite/silicon tandem solar cells. This study demonstrates that a 10 nm thin atomic layer deposited (ALD) Al(2)O(3 )masking layer on ITO enables the tandem cells to withstand the chemistry of the wet chemical metallization process. Our approach uses a screen-printed Ag seed-layer on ITO for homogeneous electroplating current distribution and a photoconversion efficiency up to asymptotic to 15% is reached. To avoid the use of any metal seed-layer on ITO, we also demonstrate a light-induced Cu plating (LIP) process. This further validates the presence of an electrical contact between the Cu electrode and both perovskite and Si cells. Finally, progress with the transfer of the native oxide barrier layer for selective electroplating (NOBLE) metallization to bifacial perovskite/silicon tandem solar cells is presented.

The use of sol-gel materials can simplify the industrial fabrication of high-efficiency silicon solar cells if a suitable deposition method is established. In this work, we investigate the possibilities to adapt a borosilicate glass sol-gel to provide a stable screen printing process. This material has previously been used as a boron dopant source for silicon solar cells. We now use an adjusted synthesis process, with an increased gelling time and different additives. This changes the rheological properties (i.e., the elastic and viscous moduli G′ and G″) in a way that avoids the dripping of paste through the screen and that stabilizes the material transfer in subsequent printing steps. Using this synthesis process, we were able to show a printing process with long-term stability of more than 500 prints. When comparing the adjusted to the initial paste, we show that, after thermal treatment, the obtained thin films are very similar in terms of their constitution, with a refractive index between n = 1.47 (initial) and n = 1.55 (adjusted). We also show that they provide the same amount of doping under the tested conditions (950 °C, 30 min), resulting in sheet resistances of R□ = (42.5 ± 2.6) Ω/□ (initial) and R□ = (46.4 ± 3.6) Ω/□ (adjusted).

A proof of principle for electrochemical screen printing (ESP) as a patterning process for thin metal stacks that can be employed, eg, in interdigitated back contact (IBC) or silicon heterojunction (SHJ) solar cells, is demonstrated. By using the ESP process, a 125 x 125-mm(2) interdigitated back contact grid was successfully patterned into a 100-nm physical vapor deposited (PVD) aluminum layer. Optimizations of the ESP process were performed to improve the patterning resolution. Rectangular trenches with a mean width of 36 +/- 5 mu m could be demonstrated on a 100-nm-thick aluminum layer. Up to now, ESP can be applied to PVD aluminum, copper, or stacks of both materials. Finally, metal stacks of aluminum and copper were structured, which allow a more homogeneous current distribution for the ESP process and additionally for the subsequent copper electroplating because of the second metal layer underneath the layer to be structured. The successful transfer from wafer substrate to polymer foils increases the application options of ESP technology enormously, where the topography of the surface to be structured affects the printing results.

Borosilicate glass films deposited by chemical vapor deposition are used as boron dopant sources in silicon solar‐cell manufacturing, to reduce the fabrication costs of, e.g., back‐contact back‐junction (BCBJ) solar cells. Herein, an alternative dopant source is investigated, which can replace such layers by a printing step. The necessary paste is synthesized by the sol–gel method and optimized for screen printing as demonstrated. The liquid paste can be converted to a glass by thermal annealing, as evaluated by spectroscopic investigations of the resulting thin films. The resulting layers are uniform and crack‐free with a thickness of around 150 nm on silicon surfaces. It is shown that such layers can act as boron dopant sources on silicon, sufficient for the fabrication of BCBJ solar cells, as demonstrated by prototype devices.

We report recent progress in the adoption of an optimized screen-printable boron dopant material, which enables the cost-competitive fabrication of novel n-type silicon solar cells such as "nPERT" and "IBC" cells. We manufactured first "IBC" devices with an early version of our dopant material, a co-diffusion approach and evaporated electrodes, achieving an efficiency of 20.9 % in 2016. Since then we optimized the dopant material and co-diffusion processes, as reported in this work. These optimizations now enable a long-term printing of the dopant material, suited for mass production, while maintaining crucial performance parameters. Moreover, we demonstrate a co-diffusion setup with POCl3, which does not require any additional dopant sources and can instead be adjusted with a wet chemical etch back. Combined with new commercially available electrode pastes, which have been evaluated with regard to simultaneous contacting of n- and p-type dopings, all screen printed n-type solar cells become a mass market possibility in the near future.

Screen printed boron doping paste can be used as a cost-effective and highly flexible dopant source in silicon photovoltaics. In combination with a co-diffusion approach, it can help mitigate some of the increased costs advanced solar cell concepts inherit. Aiming at the fabrication of high efficiency back-contact back-junction solar cells, we investigate the limitations of direct structured application regarding minimal feature sizes. We find minimal feature sizes of 75 and 120 μm for n ++ - and p ++ -doped regions, respectively. We also demonstrate a fully compatible and homogeneous (ΔR□/R□ = 3% rel ) co-diffusion process, creating all dopings at once.

Reduction in production costs is essential for newsolar cell concepts to be competitive. A large cost factor in interdigitated back-contact solar cell manufacturing is the metallization. Several process steps are needed to form an interdigitated metal pattern out of a full faced metal layer to realize n- and p-metal contacts. Generating electrically separated conductor tracks is not only a challenge in PV but also in the circuit board sector. To drive down the costs for metal structuring, an innovative approach called electrochemical screen printing (ESP), which combines screen printing and electrochemical etching is developed in this paper. It permits localized etching of aluminum layers with very short process durations. The process speed yields 100 mm/s and is comparable with the conventional screen printing speed in solar cell manufacturing. Hence, it is faster than conventional structuring processes using masks and chemical etchants. By using a self-made water-based NaNO3 paste, narrow etched grooves (<;80 μm) are formed in an aluminum layer by ESP, resulting in electrically separated aluminum regions. To increase the conductivity of the thin formed Al pattern, selective thickening is demonstrated by aluminum activation and plating nickel and copper. In this way, Al/Ni/Cu conductor tracks separated by a 70 μm trench are made out of a full faced aluminum layer using a short and simple process sequence. By electron microscopy and X-ray spectroscopy, the quality of etched regions and the structure of the formed metal stack are characterized in detail in order to assess the process sustainability.

The development and improvement of silicon solar cells is often based on a top-down approach, achieving highest conversion efficiencies and then translating it to industrial equipment and fabrication routes. This work presents an alternative option to derive research and fabrication strategies focused on cost of ownership calculations. Given the necessary tools and insight into feasible production routes, this attempt can be very helpful and rewarding for (small) research facilities, existing solar cell fabrication plants or interested investors in the solar industry. A research strategy is exemplarily derived for the goal of industrially feasible back-contact back-junction solar cells, but many aspects can be generalized for different purposes. Several different fabrication routes are shown and compared to a PERC fabrication route. We find that a co-diffusion approach can offer significant cost reduction potential on cell level, from +21 %rel down to -2%rel.

An electrochemical etching process is developed to realize the contact pattern of back contact solar cells. It combines ECM technology (Electrochemical Machining) with screen printing to allow local removal of metallic layers for maskless formation of electrically isolated conductive paths. The present work focused on waterbased paste development for this application. A plain sodium nitrate solution is used as electrolyte which allows electrochemical etching. Thickener and rheological additives are added to form a screen-printable paste. Additionally different additives are varied to improve printing paste behavior and printing results. The homogeneity of the printing paste is a major factor in the quality of etched structures. The multi-level homogenizing process developed in the present work reduces the particle size by about 35%. Using the optimized NaNO3-based paste, etched lines are formed in 100 nm aluminum layers by the Electrochemical Screen Printing (ESP) process. The smallest lines show widths of 80 μm and the adjacent aluminum regions are electrically separated up to a resistance of 1.6 MΩ. The process time is less than 2 seconds for 156x156 mm samples. Further process modifications ensure another particle size reduction of 33%. First IBC test structures are etched with line widths of 160 μm by using the novel process.

This work presents an analysis of co-diffused back-contact back-junction silicon solar cells, fabricated by utilizing screen printed boron-doping paste. The feasibility of this paste has been shown in earlier work by the authors. Due to its promising performance, comparable to earlier used boron-doped silicate glass coatings, a proof-of-principle cell run was performed yielding, several small devices with various unit cell geometries and full-wafer size devices. The achieved mean conversion efficiency of nine small devices was η = 20.9 %, while the best full-wafer size device achieved η = 20.6 %. The cells are analyzed with a focus on the significant difference between small and large cells in short circuit density (ΔJSC = -4%) and the current limitations of the built cells assessed by numerical simulations. A set of improved parameters derived from earlier work at Fraunhofer ISE suggests an efficiency potential exceeding η = 23 %. The short- and long-term measures necessary to realize this potential are described in this paper.

In this study, a new dispensing print head is introduced covering an operational width of 16 cm and therefore allowing for solar cell processing at industrial throughput rates. Like in previous ten nozzle versions, the interior paste flow was designed by computational fluid dynamics (CFD) using rheological parameters of applied Ag-pastes (commercially available pastes), including yield stress, shear thinning and wall slip behaviour. The novel print head features a homogeneous distribution of Ag-paste from an inlet supply with a diameter of Din = 2mm to an outlet slot with a width of ws = 160 mm. A first printing test followed by geometrical characterization of the dispensed contacts revealed a distribution of the contact finger width of wf = 35±1 μm across the whole wafer (156x156mm2) which demonstrates highest precision of the approach. The print head is directly integrated in an inline feasible dispensing platform, developed by ASYS GmbH. Respective nozzle plates can be customized to any desired front side grid regarding nozzle diameter, nozzle pitch and the total number of nozzles. In the actual version, the print head uses two strokes to print 100 contact fingers. Each of the 50 nozzles prints two adjacent contact fingers while moving up and down at a speed of up to vy = 700mm/s. In a first solar cell test sequence with the new 6” print head, a maximum cell efficiency of η = 21.2% on industrially preprocessed Cz-PERC samples was reached which demonstrates a successful launching of the print head.

This study presents a new developed, inline applicable dispensing platform that is equipped with an advanced version of previously introduced parallel dispensing print heads and works as drop-in-replacement in existing manufacturing lines. At process speeds of up to 700 mm.s(-1) and a substantially improved process stability, the impact of the resulting contact geometries on optical and ohmic losses was analysed in detail. A reduced finger width as well as an effective width of just 48% after encapsulation of the finger width leads to nearly 50% reduction of shading losses compared to screen printed samples. A substantially improved finger homogeneity leads to similar grid resistances at 20% less silver consumption. Consequently, recent cell results on industrial emitters (R-sh = 90 Omega/sq.) showed an efficiency increase of up to +0.4% abs. in comparison to standard single screen printing reaching top values of eta = 20.5% on PERC structures. A key improvement of the technology is the new ability to process certain metal pastes originally designed for screen printing applications and thus keep in track with fast emerging paste development. Successfully evaluated screen printing pastes then can be rheologically adapted in order to reach ultrafine contact fingers at high aspect ratios and extract the whole advantage of this non-contacting printing technology. (C) 2015 Published by Elsevier Ltd.

This work deals with a possibility to simplify the processing of back-contact back-junction solar cells. A novel metallization process without using any additional mask is presented. The main focus is set on the contact separation resulting in the interdigitated metal pattern. In case of using evaporated aluminum as contacting material to silicon, aluminum anodizing is a convenient process to convert electrically conductive aluminum to electrically isolating aluminum oxide. In the established processes in which anodizing of aluminum is used for aluminum structuring, masks are used to achieve local anodized areas. In order to make the contact separation process by anodizing more economic, several in-situ anodizing processes either using structured processing units or printing techniques are developed and tested.