Status and perspective of industrial TOPCon solar cell development at Fraunhofer ISE

This work reports on the status of industrial TOPCon solar cell development at Fraunhofer ISE. The baseline process makes use of Cz-Si:P wafers of M2 size, a TOPCon stack consisting of a thermal silicon oxide layer in combination with an 80 nm thin in-situ phosphorous-doped low-pressure chemical vapor deposited polysilicon layer as well as screen printed metal contacts. A comparison between different technologies for deposition of aluminum oxide (AlOx) layers reveals advantages for atomic layer deposition, which considerably reduces minority carrier surface recombination, and as a result leads to an overall increase in solar cell efficiency. Potential challenges in contacting by screen-printed and fired silver contacts, which might arise due to the presence of an AlOx layer on the rear side, are overcome by implementation of a laser-enhanced contact formation step, which reduces the series resistance of such solar cells by more than 2 Ωcm2. These modifications of our baseline process in combination with a new generation of metallization pastes allows for the fabrication of solar cells with a champion efficiency of 23.8%. Our stable baseline process allows for evaluation of other TOPCon-related technologies or plated contacts, as well as identifying challenges for so-called TOPCoRE solar cells.