N-Type Bi-Facial Solar Cells With Boron Emitters From Doped Pecvd Layers

Abstract

This work is mainly focused on an alternative method for emitter formation by means of boron diffusion from a boron-doped plasma-enhanced chemical vapor deposition (PECVD) doping source. With this approach only one high temperature process is necessary for emitter and BSF/FSF formation (co-diffusion), without depletion of surface doping concentration. This enables time and cost-efficient fabrication of solar cells with high conversion efficiencies, as shown in this work, on large area (156.25 cm2) bi-facial devices with conversion efficiencies up to 19.7% measured with white back sheet. Furthermore, the contact formation with screen-printing of silver/aluminum (Ag/Al) pastes and its emitter shunting behavior due to Ag/Al spikes, varying with the firing conditions in a belt furnace, are of major interest. Low contact resistance values below 4 mΩcm2 can be realized with screen-printed Ag/Al contacts on 55-70 Ω/sq PECVD boron emitters. In addition, Ag/Al spikes with a depth of around 1-3 μm could be detected with SEM measurements.