Q-Cells (Germany)

Within this work, we provide a comprehensive overview about research activities and current status with respect to rotary printed metallization for silicon solar cells. We will present the major results of the research project »Rock-Star« and previous activities which focused on the metallization of Si solar cells using flexographic printing and rotary screen printing. We demonstrate that the rear side metallization of passivated emitter and rear cells (PERC) can be realized with rotary screen printing on the same quality level as state-of-the-art flatbed screen printing. Furthermore, it is shown that both rotary screen printing and flexographic printing are able to realize the fine line front side metallization. Fine line front side contacts down to approx. 40 µm for rotary screen printing and around 30 µm for flexographic printing are demonstrated. However, further optimization is required to reduce finger width, increase finger height and thus decrease the mean lateral finger resistance. A major result of project »Rock-Star« is the development of an innovative demonstrator platform to enable rotary printed solar cell metallization with high printing speed and low cycle time per wafer. Newly developed transport, alignment and printing concept enables a cycle time of down to 0.45 s/wafer. The concept and features of the demonstrator machine are presented within this paper.

Infrared reflectometry (IRR) is a method whereby physical characteristics of a sample are rapidly extracted from the spectrum of reflected IR radiation. In the case of solar cell characterization, this provides a useful technique for high-volume inline measurement of wafer dopant content, correlated to emitter sheet resistance. IRR measurements can be used for characterizing variations in volume production and for process verification, feedback and feed-forward control. We present recent developments and experience in making the IRR technique robust for applications in solar cell emitter dopant content measurement and quality control during volume manufacturing. The IRR technology has been embodied in a commercially available product, described herein.

The surface passivation of SiO2/Al 2O3 stacks prepared at low process temperatures was investigated on phosphorous diffused n+-type Si surfaces with a broad range of sheet resistances. Two kinds of SiO2 films were prepared, the first with plasma-enhanced chemical vapor deposition (PECVD) and the second in a wet chemical process. After atomic layer deposition of the Al2O3 capping layer, the resulting SiO2/Al2O3 stacks differ in the polarity of their fixed charge density, i.e., the PECVD SiO2 stacks had a positive and the wet chemically grown SiO2 stacks a negative fixed charge density. The PECVD SiO2/Al2O3 stacks resulted in a high surface passivation over a broad range of sheet resistances whereas the wet chemically grown SiO2 stacks were only feasible for diffused surfaces with low sheet resistances (

Abstract Multicrystalline standard p‐type silicon solar cells, which undergo a potential induced degradation, are investigated by different methods to reveal the cause of the degradation. Microscopic local ohmic shunts are detected by electron‐beam‐induced current measurements, which correlate with the sodium distribution in the nitride layer close to the Si surface imaged by time‐of‐flight secondary ion mass spectroscopy. The results are compatible with a model of the formation of a charge double layer on or in the nitride, which inverts the emitter. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)