Interdigitated back contact solar cells with polycrystalline silicon on oxide passivating contacts for both polarities

Abstract

We demonstrate an independently confirmed 25.0%-efficient interdigitated back contact silicon solar cell with passivating polycrystalline silicon (poly-Si) on oxide (POLO) contacts that enable a high open circuit voltage of 723 mV. We use n-type POLO contacts with a measured saturation current density of J0n = 4 fA cm−2 and p-type POLO contacts with J0p = 10 fA cm−2. The textured front side and the gaps between the POLO contacts on the rear are passivated by aluminum oxide (AlOx) with J0AlOx = 6 fA cm−2 as measured after deposition. We analyze the recombination characteristics of our solar cells at different process steps using spatially resolved injection-dependent carrier lifetimes measured by infrared lifetime mapping. The implied pseudo-efficiency of the unmasked cell, i.e., cell and perimeter region are illuminated during measurement, is 26.2% before contact opening, 26.0% after contact opening and 25.7% for the finished cell. This reduction is due to an increase in the saturation current density of the AlOx passivation during chemical etching of the contact openings and of the rear side metallization. The difference between the implied pseudo-efficiency and the actual efficiency of 25.0% as determined by designated-area light current–voltage (I–V) measurements is due to series resistance and diffusion of excess carriers into the non-illuminated perimeter region.