DopLaCell: a new c-Si solar cell based on laser processing of dielectric films

Abstract

In this paper we introduce a new crystalline silicon (c-Si) solar cell fabrication technology based on the laser processing of dielectric films to create all the highly-doped regions. We call it DopLaCell (Doped by Laser Cell) structure. The resulting fabrication process can be simplified to just four steps: wafer cleaning, film depositions, laser processing and metallization. We used phosphorus-doped silicon carbide stacks (SiCx(n)) and aluminium oxide/silicon carbide (Al2O3/SiCx) stacks for the creation of n+ and p+ regions respectively. As a proof of concept, 1x1 cm2 solar cells were fabricated on 0.45 Wcm p-type substrates with promising results. The main feature of DopLaCell structure is the location of the emitter at the rear surface consisting of a point-like laser processed n+ regions combined with an induced inversion layer in between based on the fixed charge density of the SiCx(n) stacks. Solar cells with distance between rear emitter regions or pitch ranging from 200 to 350 μm are characterized resulting in a strong decrease of Fill Factor (FF) from 75.4 to 59.7 %. Suns-Voc measurements show excellent pseudo-FF (p-FF) values beyond 81% in all devices demonstrating the high quality of laser doping process and the actual limitation of FF by ohmic losses. Device modelling through 3D simulations demonstrates that these ohmic losses are related to the high sheet resistance of the inversion layer induced in-between n+ regions. We conclude that there is room for improvement to fully develop the potential of this new structure, particularly for low resistivity n-type substrates where the high fixed charge densities of Al2O3 can help to improve FF.