Co-Diffused Back-Contact Back-Junction Silicon Solar Cells with a Novel Screen-Printed Boron-Doping Paste

Abstract

Back-contact back-junction silicon solar cells feature high conversion efficiency and have since their introduction been of interest for the photovoltaic community. The interdigitated back-contact design reduces shading losses during illumination but is more complex compared to conventional cell concepts, hampering the industrial integration. This issue has been addressed in research conducted by Fraunhofer ISE and Merck KGaA with the introduction of a screen-printable boron-dopant paste. It allows for cost-reduction in established process routes and enables novel co-diffusion processes with a huge potential. The use of screen-printing avoids high investment costs and makes use of a widely adopted technology. The boron emitter formed during a POCl3:O2:N2 co-diffusion process has been characterized by secondary ion mass spectroscopy (SIMS) and quasi-steady state photo conductance (QSSPC). Besides that, a proof-of-principle cell batch has been fabricated based on reference work, with a mean efficiency of 20.9 % over 9 cells (aperture size 4 cm²).