Researchers from the Institute for Solar Energy Research Hameln (ISFH) and Leibniz Universität Hannover in Monocrystalline silicon solar cell with POLO-contacts for both polarities on the solar cell rear side. In the foreground the rear side of seven solar cells processed on one wafer can be seen. Source: ISFHGermany have developed a crystalline silicon solar cell with an independently confirmed efficiency of 26.1 percent under one sun. This world record for p-type silicon material was achieved with a passivating electron-selective n+ type polysilicon on oxide (POLO) junction and a hole-selective p+ type POLO junction.

The high selectivity of POLO junctions is a key factor in generating such high efficiencies. These structures are applied in an interdigitated pattern on the rear side of cells in order to minimize parasitic absorption in the poly-Si and avoid shading by front side metallization.

The n+-type and p+-type poly-Si junctions are separated from each other by an intrinsic poly-Si region. Doped regions are structured using lab-type processes, but the opening of the dielectric rear-side reflector is realized by local laser ablation.

The final objective is to integrate POLO junctions into the current mainstream technology with a clear advantage in efficiency. “Replacing photolithography by laser contact opening is a first important step towards industrialization as it enables screen-printing-based metallization,” states ISFH researcher Prof. Robby Peibst.