Large-Area Back-Contact Back-Junction Solar Cell With Efficiency Exceeding 21%

In this study, high-efficiency solar cells are presented with the use of low-cost industrially available technologies. This results in the so-called ZEBRA concept: a litho-free process in which standard 156 × 156 mm2 monocrystalline n-type Cz-Si wafers are processed into high-efficiency interdigitated back-contact solar cells. In our first attempt, we obtained energy conversion efficiencies of more than 20% on 239 cm2 area. With the help of a 3-D simulation of the device, a further improvement to more than 21.5% was determined. We indentify the open-circuit voltage and the large serial resistance as the main losses impeding from reaching the simulated efficiency. The cell results after an extensive optimization are presented in this study, focusing on the improvement of the fill factor of the cells. The optimized solar cells show an improvement in the energy conversion efficiency up to 21%. Furthermore, the simple metallization and the module interconnection design of the ZEBRA cells allow for a bifacial application. Indoor and outdoor I - V measurements on a bifacial one-cell-module show an enhancement in the total generated power of more than 12% as compared with a monofacial module.