N-type silicon solar cell with rear tunnel oxide combined with rear screen-printed electrodes

In this article, we describe an n-type silicon solar cell with a conversion efficiency of 21.9% on a 156 mm pseudosquare Czochralski (Cz) wafer with a rear tunnel oxide-passivated structure and rear screen-printed electrodes. The thermal degradation of the rear structure during electrode firing was solved by adding a SiNx film on the rear surface. Not only the SiNx film but also the tunnel oxide structure was chemically etched using firethrough screen-printed electrodes, so that the electrodes contacted directly to the bulk silicon. A phosphorus-diffused layer appeared at the bulk silicon immediately below the tunnel oxide, and this shallowly and densely diffused layer reduced the contact resistivity between the electrodes and the bulk silicon layer. Degradation of rear passivation caused by etching on the tunnel oxide structure was improved by adding a diffused layer using POCl3 before chemical oxidation. The diffused layer using POCl3 was deep and had a low phosphorus concentration, thus the field effect worked successfully while Auger recombination was not enhanced. (C) 2018 The Japan Society of Applied Physics