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

Abstract

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 Voc of 653 mV, short-circuit current density Jsc 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 J0e of 101 fA/cm2, and base saturation current density J0b of 259 fA/cm2 respectively. This demonstrates the potential of this novel technology for production of low-cost high-efficiency cells.