Electrically conductive adhesives as cell interconnection material in shingled module technology

Abstract

Modules, in which pre-cut crystalline silicon solar cells-or shingles-are assembled into solar modules by placing the pre-cut cells in a shingle-like way on top of each other, have gained a lot of market attention in the last years. Such cell lay-up in the module has as main advantage an increased module output, due to more efficient packing without inactive space between cells. An additional benefit is that no important modifications to the cell production process are needed. The first commercial market-available modules use electrically conductive adhesives (ECAs) to connect the precut cells into strings. This paper will demonstrate that using ECAs with optimized properties will result in reliable solar modules. Adhesive properties such as adhesion strength, Young's modulus, volume resistivity and contact resistance are shown in combination with the thermocycle reliability data of ECA-assembled modules. Application techniques suitable for high-volume manufacturing are demonstrated. PURPOSE Most solar modules currently on the market are built up from ribbon-attached crystalline H-pattern cells in which the cells are side by side to each other and ribbons are interconnecting to these cells via soldering. The advantage of this approach is the low-cost interconnection and the robustness of the technology. However, there are some disadvantages to this module design such as high resistive losses and the incompatibility with very thin wafers. One of the new, promising advances for module assembly is a shingled cell technique whereby pre-cut crystalline cells are placed like roof tiles on top of each other (Fig. 1). Interconnection of the different pre-cut crystalline cells is achieved via electrically conductive adhesives (ECAs), which have an advantage over soldering in that they can absorb stresses due to CTE mismatches in the module. FIGURE 1. Assembly scheme of pre-cut cells with electrically conductive adhesives

Design considerations for multi-terawatt scale manufacturing of existing and future photovoltaic technologies: challenges and opportunities related to silver, indium and bismuth consumption

“…For shingled modules, each full-area solar cell is cleaved into 5 or 6 strips (also known as shingles), and those strips are 'shingled' together like roof tiles on the long edge and bonded with an electrically conductive adhesive (ECA). 88,89 This approach eliminates the need of a conventional soldering process as well as the gap between each cell that is normally required in most ribbon-connected modules. As such, the packing density can be improved, and optical shading losses from busbars, soldering tabs and ribbons can be avoided.…”

“…Alternative abundant low-temperature solder alloys must also be investigated. The use of electrically conductive adhesives should also be considered, which have been used for the interconnection of shingled solar cells, 88,91 provided that such adhesives do not contain silver or other scarce elements.…”

“…For example, investigating the use of tin-bismuth coatings with substantially lower bismuth contents, or alternatively the use of electrically conductive adhesives, which have been used for the interconnection of shingled solar cells. 88,91 Collectively, while the current implementations of industrial TOPCon and SHJ solar cells do not create an opportunity for substantially increased sustainable manufacturing capacity over PERC, two-terminal tandem devices are exciting highefficiency solar cell structures, which feature a unique opportunity to provide improved sustainability over the current dominant PERC solar cell technology. Firstly, there are natural benefits of significantly higher solar cell efficiencies in the vicinity of 30%.…”

Debondable adhesives and their use in recycling

“…251 Functional electrically conductive adhesives (ECAs) have been proposed. 252 These pose a quandary as whilst they impose a challenge at end-of-life from a materials separation perspective, they also impart useful functional properties, and can contribute to efficient photovoltaic module design. Using ECA's can reduce the need for lead solders, 250 which reduces the handling of toxins in manufacturing and at the end of life and aid compliance with Restriction of Hazardous Substances (RoHS) legislation.…”

Freestanding and supported processing of sub-70 μm kerfless epitaxial Si and thinned Cz/FZ Si foils into solar cells: An overview of recent progress and challenges

“…These pastes are commonly used for solar cell interconnection, e.g. in shingling applications [63]. The important difference between ECAs and regular metallisation pastes used for solar cell metal grid printing lies in the composition of the paste.…”