IEEE TRANSACTIONS ON COMPONENTS, PACKAGING AND MANUFACTURING TECHNOLOGY, VOL. 1, NO. 9, SEPTEMBER 2011 1319 Developing an Advanced Module for Back-Contact Solar Cells Jonathan Govaerts, Jo Robbelein, Mario Gonzalez, Ivan Gordon, Kris Baert, Ingrid De Wolf, Senior Member, IEEE, Frederick Bossuyt, Steven Van Put, and Jan Vanfleteren, Member, IEEE Abstract—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 lam- ination; 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. Index Terms— Embedding, solar modules, thin cells. I. I NTRODUCTION U P UNTIL now, and probably for still some time to come, crystalline silicon solar cells are and will be the most prevalent type of photovoltaic technologies around, accounting for over 90% of the electricity generated by solar energy worldwide. Motivated by the prospect of a clean, renewable, unlimited—or rather, nondepleting for the foreseeable future and beyond—and independent supply of energy, government and private incentives alike have a significant impact in bringing solar electricity within the reach of the general public in the developed world. However, to further lower the price Manuscript received March 19, 2010; revised June 2, 2011; accepted June 13, 2011. Date of publication September 6, 2011; date of current version September 21, 2011. Recommended for publication by Associate Editor T.-C. Chiu upon evaluation of reviewers’ comments. J. Govaerts, J. Robbelein, M. Gonzalez, I. Gordon, and K. Baert are with imec, Leuven 3001, Belgium (e-mail: jonathan.govaerts@gmail.com; jo.robbelein@imec.be; mario.gonzalez@imec.be; ivan.gordon@imec.be; kris. baert@imec.be). I. De Wolf is with imec, Leuven 3001, Belgium. He is also with the Department of Metallurgy and Materials Engineering, Katholieke Universiteit Leuven, Leuven 3001, Belgium (e-mail: ingrid.dewolf@imec.be). F. Bossuyt, S. Van Put, and J. Vanfleteren are with imec, Leuven 3001, Belgium. They are also with the Department of Electron- ics and Information Systems, Universiteit Ghent, Ghent 9000, Bel- gium (e-mail: frederick.bossuyt@elis.ugent.be.be; svanput@intec.ugent.be; jan.vanfleteren@elis.ugent.be). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TCPMT.2011.2161082 of solar electricity, and to make it available to an even wider public, e.g., in the developing nations as well, it is important that the production cost is still substantially lowered. In the long run, thin-film, and organic photovoltaics (PVs) seem very promising in this respect, but on a shorter term, and for higher- efficiency applications, lowering the price of crystalline silicon solar panels is very much desirable. There are of course a number of ways to tackle this issue, ranging from lower temperature processing and cheaper mate- rials to higher throughput systems and improved efficiencies. Here, the idea is to embark on the widely followed route of evolution toward ever thinner cells. This serves the purpose of cutting cost by reducing the amount of silicon needed, but it could also be beneficial in minimizing possible future issues with the supply of solar-grade silicon [1]. The conventional approach for manufacturing modules widely adopted for modules based on front- and back- contacted cells is, e.g., described in [2]. This technology is very mature but was developed for cells requiring out-of- plane interconnection between the front of one cell and back of the neighboring cell. When considering back-contact cells however, it is worth questioning whether such a technology is still optimal and preferable. For reference, a range of types of crystalline silicon back-contact solar cells and their link with conventional cells, as well as a comparison between conven- tional modules and adapted module manufacturing based on back-contact solar cells, are given in [3]. The current state of the art in back-contact module manu- facturing (up to now, conventions are still too much lacking in this field to speak of a “conventional” approach) is exemplified by the approaches put forward by, e.g., SunPower [4], Energy Research Centre of the Netherlands [5], the Schott–Solland collaboration [6], and Advent Solar-Applied Materials [7], also Photovoltech and Bosch have already shown demonstration modules with similar technology. Broadly, they can be clas- sified into two categories: conventional module technology and monolithic module assembly (MMA), shown in Fig. 1. Both approaches are based on assembly using dry lamination with ethylene vinyl acetate (EVA), whereas for interconnection the conventional approach uses a tabbing/stringing process, and monolithic module assembly encompasses a module- level interconnection technique based on conductive foils and adhesives. (The Schott–Solland approach could be considered a hybrid, as the module is first laminated, and then the ribbons are laser-soldered to the cells through the laminated layers, and therefore referred to as in-laminate laser soldering). 2156–3950/$26.00 © 2011 IEEE