One approach to overcome the limitations of a conventional front-contacted solar cell is to move both the p-n junction and the back surface field (BSF) to the rear side of the solar cell. This architecture is referred to as the interdigitated back contact (IBC) solar cell. The concept of the IBC solar cell was first proposed by Lammert and Schwartz [M. D. Lammert and R. J. Schwartz, “The interdigitated back contact solar cell: a silicon solar cell for use in concentration,” IEEE Translations on Electron Devices, vol. 24, no. 4, pp. 337-342, 1977].
By moving both the p-n junction and BSF to the rear, all metallization required to extract generated carriers is also moved to the rear side. The front, sunward side is therefore free from shading losses, enabling higher short circuit current and thus efficiency. The front surface no longer needs a heavily diffused layer optimized for metal contact, but instead can be optimized to create a front surface field (FSF) which minimizes recombination losses at the front surface thereby increasing the open circuit voltage and thus efficiency. Another advantage of having metal contacts on the rear side is that the metal geometry is no longer constrained to minimize shading losses, allowing for wider metal which reduces resistive losses. Having all metal contacts on the back side also has the added benefit of simplifying integration of solar cells into a module.
Various methods have been suggested with regard to the manufacturing process of the IBC cell. Such methods are described in P. J. Verlinden, R. M. Swanson and R. A. Crane, Prog. Photovolt: Res. Appl. 2, 143-152 (1994); F. Granek, “High-Efficiency Back-Contact Back-Junction Silicon Solar Cells,” PhD Thesis, Fraunhofer Institute (ISE), Freiburg, Germany (2009); D-H. Neuhaus and A. Munzer, “Review Article: Industrial Silicon Wafer Solar Cells,” Advances in OptoElectronics, Volume 2007, Article ID 24521, doi: 10.1155/2007/2451; US 2011/0003424; and US2010/0081264.
Fabricating an IBC solar cell requires creating three doped regions. Typically these three regions are (i) a phosphorus doped front surface field (FSF), (ii) a phosphorus doped back surface field (BSF), and (iii) a boron emitter. These three regions are usually created using three separate diffusion steps making the fabrication of IBC cells complex and cost prohibitive.
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