ITO-free metallization for interdigitated back contact silicon heterojunction solar cells

We report on two different approaches to fabricate interdigitated back contact silicon heterojunction solar cells without using indium tin oxide (ITO). The standard ITO/Ag backend is either modified by replacing ITO with aluminum-doped zinc oxide (AZO) or completely replaced by a sole aluminum (Al) layer. The very transparent AZO enhances the optical properties at the rear side resulting in an increase in short-circuit current density. The efficiency of the AZO cells remains on the level of the ITO ones, as the fill factor drops slightly. On the contrary, the contact resistivity of annealed Al, in comparison to ITO and AZO, to the emitter and BSF layers is much lower, thus the fill factor is increased. Despite lower open circuit voltages, cells with Al achieve efficiencies of up 22 %, a gain of 0.5 %abs compared to the ITO reference.