High efficiency n-type solar cells with screen-printed boron emitters and ion-implanted back surface field

Formation of low-cost boron-doped emitters for mass production of n-type silicon solar cells is a major challenge in the PV industry. In this paper, we report on commercially viable screen printing technology to create boron emitters. A screen-printed boron emitter and phosphorus implanted back surface field were formed simultaneously by a co-annealing process. Front and back surfaces were passivated by chemically-grown oxide/PECVD silicon nitride stack. Front and back contacts were formed by traditional screen printing and firing processes with silver/aluminum grid on front and local silver contacts on the rear. This resulted in 19.3 % high efficient large are (239cm²) n-type solar cells with an open-circuit voltage V_oc of 653 mV, short-circuit current density J_sc of 37.7 mA/cm², and fill factor FF of 78.3 %. Co-diffusion and co-firing reduced the number of processing steps compared to the traditional technologies like BBr₃ diffusion. Detailed cell analysis gave a bulk lifetime of over 1 ms, the emitter saturation current density J_0e of 101 fA/cm², and base saturation current density J_0b of 259 fA/cm² respectively. This demonstrates the potential of this novel technology for production of low-cost high-efficiency cells.