Influence of laser power on POCl3 diffused back surface field on n-type PERT silicon solar cells with local back contact

We report n-type passivated emitter rear totally diffused (PERT) silicon solar cells with local back contacts (LBC) formed by laser process. With passivated back surface field (BSF), the PERT cell design shows an improved open circuit voltage (Voc) with reduced recombination at the rear due to improved optical confinement. The rear side was diffused by POCl3 diffusion with low sheet resistance (Rs) BSF and passivated using SiNx. Laser ablation was used to open the SiNx on the rear for LBC. The Nd:YAG laser power (mW) parameters and POCl3 doping temperature were varied to obtain the BSF with lower sheet resistance. Laser power of 44 mW with 10 kHz resulted in 30 Ω/sq BSF layer with effective lifetime (τeff) of 90 μs and a higher Voc of 646 mV. With the optimized laser parameters the best electrical results yielded a short circuit current density (Jsc) of 36 mA/cm2 and efficiency of 18.54%.