Laser-Doped Selective Emitter - Process Development and Speed-Up

This study pursues the development of a laser-doped selective emitter (LDSE) for p-type silicon passivated emitter and rear solar cells with screen-printed and fired silver contacts on the front. The LDSE is formed via local laser doping from the two-layer stack system of phosphosilicate glass and silicon dioxide that is located on the wafer surface after tube furnace diffusion using phosphorus oxychloride (POCl3) as liquid dopant precursor. We aim for minimum emitter dark saturation current density at the LDSE-metal interface j0e,met and minimum specific contact resistance c. We use both an atmospheric pressure POCl3 diffusion process and a high throughput low pressure POCl3 diffusion process. Both POCl3 processes are combined with a green nanosecond laser process at wavelength = 532 nm and pulse repetition rates 60 kHz < frep < 100 kHz. Furthermore, we investigate high-speed infrared laser processes at = 1064 nm and frep = 2 MHz for which heat accumulation is expected to become relevant during LDSE formation. For some of the tested laser processes within this work, c ≈ 1 mOcm2 is achieved. At the same time, simulations with the Quokka3 skin solver that are based on the LDSE doping profiles show that the LDSEs have the potential to lead to a j0e,met reduction by more than 50% compared to the not laser-doped emitter.