Abstract
Silicon n-type n+np+ solar cells offer many advantages over conventional n+pp+ cells, including better resistance to light-induced degradation and higher conversion efficiency potential. However, the formation of the p+ emitter in n+np+ cells requires high diffusion temperatures and the use of alternative boron dopants is necessary to overcome the limitations of conventional processes. This study explored aluminium, gallium and gallium/boron co-doping as p-type dopants for the fabrication of thin (140 µm) n+np+ solar cells. The results showed that aluminium is not suitable for the formation of the p+ emitter due to its low solid solubility in silicon and its high segregation towards silicon oxide. Gallium required high diffusion temperatures and suffered from a degradation of the concentration profile in later stages of the manufacturing process, leading to poor performing solar cells. Gallium/boron co-doping has proved to be a promising alternative to boron. Thin n+np+ solar cells doped with GaB achieved a maximum conversion efficiency of 13.7%, slightly lower than that of boron-doped cells (14.9%). Optimisation of the GaB diffusion process and surface passivation could further improve the performance of these cells. This study demonstrates the potential of gallium/boron co-doping for the manufacture of new-generation thin n+np+ solar cells. Further research is needed to fully exploit the advantages of this technology and contribute to improving the efficiency and cost of silicon solar cells.

Key words: n np silicon solar cells, gallium doping, boron doping, co-doping, surface passivation.