Developing an advanced module for back-contact solar cells

This paper proposes a novel concept for integrating ultrathin solar cells into modules. It is conceived as a method for fabricating solar panels starting from back-contact crystalline silicon solar cells. However, compared to the current state of the art in module manufacturing for back-contact solar cells, this novel concept aims at improvements in performance, reliability, and cost through the use of an alternative encapsulant, namely silicones as opposed to ethylene vinyl acetate, an alternative deposition technology, being wet coating as opposed to dry lamination; and alternative module-level metallization techniques, as opposed to cell-level tabbing-stringing or conductive foil interconnects. The process flow is proposed, and the materials and fabrication technologies are discussed. As the durability of the module, translated into the module's lifetime, is very important in the targeted application, namely solar cell modules, modeling and reliability testing results and considerations are presented to illustrate how the experimental development process may be guided by experience and theoretical derivations. Finally, feasibility is demonstrated in some first proofs of the concept, and an outlook is given pointing out the direction for further research

Stress-induced lift-off method for kerf-loss-free wafering of ultra-thin (∼50 μm) crystalline Si wafers

International audienceWe present a new wafering method for the production of ultra-thin crystalline silicon. This new lift-off process, named SLIM-cut (for Stress-induced LIft-off Method), requires only the use of a screen-printer and a belt furnace; no ion-implanted, porous layer or additional thickening by epitaxy is needed to obtain high quality wafers in the thickness range of 50 μm without kerf loss. We deposit on a thick substrate a layer with mismatched coefficient of thermal expansion with respect to the substrate (for instance a metal layer). Upon cooling, the differential contraction induces a large stress field, which is released by the initiation and the propagation of a crack parallel to the surface. The concept has already been demonstrated successfully on both single and multi-crystalline silicon. Very clean self-standing crystalline films with an area of 25 cm2 have been obtained from a high quality wafer. Some Si layers were further processed into solar cells. The first unoptimized solar cell device with a very simple process (no back-surface field, no intentional texturing, heterojunction emitter) showed an energy conversion efficiency of 10.0% (1 cm2). This represents a silicon consumption already as low as 3.1 g/Wp (taking into account a polishing loss of 50 μm), and proves the conservation of the material quality during the process. The potential of the method is estimated by the development of a custom-made numerical model. The model uses a 2D finite element method and is able to propagate a crack in a multi-layered structure. The model proposes a concentric re-meshing in the region of the crack tip at every increment and a crack initiation and propagation based on maximum stress criteri

Gettering effects and FG annealing on thin RST ribbon silicon solar cells

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Studies of implanted boron emitters for solar cell applications

International audienceB implanted emitters are investigated in the back junction cell configuration and their material properties are tested in double side implanted Si wafers. B has been implanted at 5 keV at various dose conditions varying from 1 Â 10 14 up to 3 Â 10 15 at./cm 2 and activated at 10008C for 10 min. N-type 8 Â 8 cm 2 mono-crystalline cells are fabricated and measured. Both fill factor and efficiency increase for high-B doses. However, at 10 15 at./cm 2 B dose the V oc drops, which is in agreement with lifetime degradation in the wafer. Defect evolution simulations of B n I m clusters formation is correlated with lifetime degradation

Development of solar cells on RST-ribbons

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Performance of a new type of module based on back-contact solar cells

Imec has developed a new technology to integrate and interconnect back-contact solar cells into modules, based on embedding cells in silicone on top of a glass substrate. This technology aims at an improved optical performance and reliability (through the use of silicones and low-temperature metallization). One of the additional advantages is that the technology is suitable for integrating very thin cells into modules: whereas standalone interconnection of such fragile thin cells, e. g. tabbing and stringing, would significantly lower the throughput yield due to breakage, the cells are better protected if they are embedded inside silicone. The paper will first elaborate on the process flow, the background and motivation, advantages, drawbacks and limitations, and technical aspects of the developed technology. Then it will present the results of the measurements on the performance of functional solar cells processed into modules using this technology, discussing losses and loss mechanisms. Then, the approach towards determining the reliability of the module will be presented, indicating how imec aims at building up an ageing model, and elaborating the results on the failure mode and effect analysis, modeling, characterization and reliability testing