Silicon-based passivating contacts: The TOPCon route

Passivating contacts based on poly-Si/SiOx structures also known as TOPCon (tunnel oxide passivated contacts) have a great potential to improve the efficiency of crystalline silicon solar cells, resulting in more than 26% and 24% for laboratory and industrial cells, respectively. This publication gives an overview of the historical development of such contact structures which have started already in the 1980s and describes the current state-of-the-art in laboratory and industry. In order to demonstrate the great variety of scientific and technological research, four different research topics are addressed in more detail: (i) the superior passivation quality of TOPCon structures made it necessary to re-parametrize intrinsic recombination in silicon, (ii) the control of diffusion of dopants through the intermediate SiOx layer is essential to optimize passivation and transport properties, (iii) single-sided deposition of the poly-Si layer would reduce process complexity for industrial TOPCon cells, and (iv) silicon-based tunnel junctions for perovskite-silicon tandem cells can be fabricated using the TOPCon technology.