Large area back-contact back-junction solar cells with efficiency exceeding 21%

In this work high efficiency solar cells are fabricated with the use of low-cost industrially available technologies. The solar cell concept is called ZEBRA: a litho-free process in which standard 156×156 mm² monocrystalline n-type Cz-Si are processed into high efficiency Interdigitated Back Contact (IBC) solar cells. In our first trial we obtained conversion efficiencies of more than 20% on solar cells with 239 cm² area. With the help of a three-dimensional simulation of the device, a further improvement to more than 21.5% was demonstrated. We indentify the open-circuit voltage and the series resistance as the main losses to achieve the simulated efficiency. After an extensive optimization, targeting mainly the improvement of the fill factor, the cell results are presented in this work. The optimised solar cells show an improvement in the energy conversion efficiency of up to 21%. Furthermore, the simple metallization and the module interconnection designed for the ZEBRA cells allow for a bifacial application. Indoor and outdoor measurements on single-cell modules show an enhancement in the generated power of up to 12% at one sun front illumination conditions.