Status and perspectives on n-type silicon solar cells with aluminium-alloyed rear emitter

This study summarises a detailed characterisation of structural and electrical properties of full-area and local aluminium-doped p+ Si (Al-p+) regions alloyed from screen-printed pastes for the application as rear emitters in n-type silicon solar cells. We discuss the impact of the Al doping profile depth on the saturation current density for non-passivated and surface-passivated full-area Al-p+ emitters and show the prerequisites for an effective passivation. The influence of a modified Al paste composition on the alloying process of local Al-p+ structures is demonstrated. The results of these investigations have enabled us to further improve the performance of our n+np+ Al rear emitter solar cells featuring a homogeneous phosphorus-diffused n+ front surface field and aerosol-printed and silver-plated front contacts. For large-area n-type Si solar cells (143.5 cm2) with a full-area surface-passivated Al-p+ rear emitter, we have achieved a record-high efficiency of 20.0 %. Solar cells with local Al-p+ emitters in the passivated rear Si surface have reached an efficiency of 19.7 %, fabricated by using a simplified processing sequence and, thus, turning out to be a very promising cell concept.