SPLTRAK Abstract Submission
High Throughput Boron Emitter Formation from Pre-deposited APCVD BSG Layers for TOPCon Solar Cells
Marius Me▀mer1, Sattar Bashardoust1, Udo Belledin1, Sven Seren2, Heiko Zunft2, Sebastian Mack1, Andreas Wolf1
1Fraunhofer Institute for Solar Energy Systems ISE, Freiburg, Germany
/2Gebr. SCHMID GmbH, Freudenstadt, Germany

The photovoltaic (PV) industry is currently looking for a cost-effective way to transfer the tunnel oxide passivated contact (TOPCon) solar cells into mass production. The TOPCon process still faces high costs, as, apart from higher metallization cost, also boron-diffusion requires much higher temperatures and longer process times compared to the POCl3-diffusion for PERC solar cells, the current working horse in the PV industry. This work presents an alternative boron diffusion approach for TOPCon solar cells enabling a highly increased throughput compared to the typically used BBr3 diffusion. We use atmospheric pressure chemical vapor deposited (APCVD) borosilicate glass (BSG) layers as the boron dopant source and combine them with a subsequent thermal anneal for dopant drive-in. Here, stacking of the wafers enables a 4 to 5 times higher throughput for the thermal process. For evaluation of this approach, we process samples with APCVD BSG layers either in a conventional single slot quartz boat configuration, or in a vertical wafer stack configuration with the wafer surfaces in direct contact to each other. In addition, a BBr3-diffusion serves as a reference process. We observe that for pre-deposited APCVD BSG layers, stacking the wafers reduces the sheet resistance compared to single slot configuration, which we attribute to the reduced interaction of the stacked wafer surface with the oxygen process atmosphere. The first implementation of this approach in industrial TOPCon solar cells already yields up to η = 22.5% peak energy conversion efficiency for the stacked wafers with APCVD BSG layers, compared to η = 22.7% for the APCVD BSG single slot configuration and η = 22.9% for the BBr3-diffused reference solar cells.