Hydrogen passivation of laser-induced defects for silicon solar cells

Abstract

Hydrogen passivation of laser-induced defects is shown to be essential for the fabrication of laser doped solar cells. On first generation laser doped selective emitter solar cells where open circuit voltages are predominately limited by the full area back surface field, a 10 mV increase and 0.4 % increase in pseudo fill factor is observed through hydrogen passivation of defects generated during the laser doping process resulting in an efficiency gain of 0.35 % absolute. The passivation of such defects becomes of increasing importance when developing higher voltage devices, and can result in improvements on test structures up to 25 mV. On n-type PERT solar cells, an efficiency gain of 0.7 % absolute is demonstrated with increases in open circuit voltage and pseudo fill factor by applying a short low temperature hydrogenation process incorporating minority carrier injection using only hydrogen within the device. This process is also shown to improve the rear surface passivation increasing the short circuit current density from long wavelengths 0.2 mA/cm2 compared to that achieved using an Alneal process. Subsequently an average efficiency of 20.54 % is achieved.