Process Development for a High-throughput Fine Line Metallization Approach Based on Dispensing Technology

AbstractIn order to enhance prosperous dispensing technology towards an industrial application, besides a continuous process development, especially throughput rate has to be increased. In this study, paste rheology of two different dispensing pastes was transferred to CFD-simulation (CFD: Computational Fluid Dynamics) to investigate different nozzle geometries and print head designs. In the following, a single nozzle dispensing setup was used to verify simulative values by comparing them with those obtained from experimental investigations. Consequently, the single nozzle process was scaled to a parallel application, where a homogeneous pressure and flow distribution within the print head turned out to be crucial to achieve a homogeneous mass flow at all nozzles. In various iteration steps, the influence of fabrication tolerances especially concerning the nozzle geometry was isolated and print head designs were optimized based on CFD towards maximum process stability. Based on these results, a novel 10 nozzle fine line dispensing unit was designed and fabricated. Finally, successful cell production with resulting finger widths of less than 35μm could be demonstrated using the novel prototype

Aluminum alloying in local contact areas on dielectrically passivated rear surfaces of silicon solar cells

We present a detailed study on the rear contact formation of rear-surface-passivated silicon solar cells by full-area screen printing and alloying of aluminum pastes on the locally opened passivation layer. We demonstrate that applying conventional Al pastes exhibits two main problems: 1) high contact depths leading to an enlargement of the contact area and 2) low thicknesses of the Al-doped p+ Si regions in the contact points resulting in poor electron shielding. We show that this inadequate contact formation can be directly linked to the deficiently low percentage of silicon that dissolves into the Al-Si melt during alloying. Thus, by intentionally adding silicon to the Al paste, we could significantly improve the contact geometry by reducing the contact depth and enlarging the Al-p+ thickness in the contact points, enabling a simple industrially feasible way for the rear contact formation of silicon solar cells

Druckkopf, Aerosol-Drucker und Aerosol-Druckverfahren

Die Erfindung betrifft einen Druckkopf (1) mit zumindest einer Aerosolkammer (10), zumindest einem Aerosolröhrchen (11) mit einem ersten Ende (111) und einem zweiten Ende (112) und zumindest einer Druckdüse (12), wobei im Betrieb des Druckkopfes (1) der Druckdüse (12) ein Aerosol aus der Aerosolkammer (10) über das Aerosolröhrchen (11) zuführbar ist und das Aerosol von der Aerosolkammer (10) zur Druckdüse (12) mittels einer laminaren Strömung transportierbar ist. Weiterhin betrifft die Erfindung ein Aerosol-Druckverfahren, enthaltend die folgenden Schritte: Erzeugen eines Aerosols, Einbringen des Aerosols in zumindest eine Aerosolkammer (10), Einbringen einer laminaren Strömung eines Hüllgases in die Aerosolkammer (10) und Transportieren des Aerosols von der Aerosolkammer (10) zur Druckdüse (12) durch ein Aerosolröhrchen (11) mittels der laminaren Strömung

Fine line printed and plated contacts on high ohmic emitters enabling 20% cell efficiency

The contact performance of seed-layer printed, fired and plated (SFP) contacts were studied on solar cells with different emitter sheet resistivities. For the seed layer of the SFP-contacts a special metal ink called SISC (seed layer ink for the metallization of solar cells), developed and fabricated at Fraunhofer ISE to contact lowly doped emitters was used. The doping profile and the surface concentration of active phosphorus are determined by secondary ion mass spectroscopy (SIMS) and by electrochemical capacitance voltage (ECV) measurements. Large-area Cz-silicon solar cells 12.5 � 12.5 cm2 were fabricated with sheet resistivities between 40 ¿/sq. and 130 ¿/sq. The cells are metalized with SFP-contacts and conventional screen print contacts for comparison. High fill factors above 79% on solar cells with lowly doped emitters (sheet resistance of 130 ¿/sq.) could be achieved with SFP-contacts. In contrast, for screen-printed contacts using standard Ag paste the FFs for such lowly doped emitters are reduced to values around 55%. The difference in contact formation is explained by contact resistance measurements together with images from the metal semiconductor junction. Using the SISC ink solar cells with 45 ¿m wide contact structures were processed on a high efficiency cell structure with a passivated rear surface and a 110 ¿/sq. emitter a FF of 81% was achieved resulting in a cell efficiency of ¿=20.6%

Combining laser chemical processing and aerosol jet printing: A laboratory scale feasibility study

First results showing the viability of combining laser chemical processing (LCP) and aerosol jet printing (AJP) technologies to produce a high-efficiency front side for silicon solar cells are presented. LCP simultaneously opens the anti-reflection coating (ARC) and highly dopes the underlying silicon to create a selective emitter, while AJP is the first in a two-step fine-line contact formation procedure. The electrical properties as well as the morphology of the resulting structures are presented. Performance similar to that achieved with evaporated TiPdAg metallization is demonstrated