A technique to make poly-Si (p(+))/SiOx contacts for crystalline silicon solar cells based on doping PECVD intrinsic amorphous silicon (a-Si) by means of a thermal BBr3 diffusion process is demonstrated. The thickness of the a-Si layer and the temperature of the boron diffusion are optimized in terms of suppressing carrier recombination and transport losses. Different interfacial layers are studied, including ultra-thin SiOx grown either chemically or thermally, and stacks of SiOx and SiNx. While the double SiOx/SiNx interlayers do not achieve the desired performance, both kinds of single SiOx layers produce satisfactory passivating contacts, with both a low recombination current and a low contact resistivity. By adjusting the boron diffusion temperature, recombination current parameter J(0) values of similar to 16 fA/cm(2) to similar to 30 fA/cm(2) have been obtained for structures with initial a-Si thicknesses of 36-46 nm, together with a contact resistivity of similar to 8 m Omega cm(2). (C) 2016 Elsevier B.V. All rights reserved.