Influence of boron doping profile on emitter and metal contact recombination for n-PERT silicon solar cells

Abstract

Increasing interest in n-type silicon (Si) solar cells due to the high-quality material properties of the n-Si wafers, their relatively low sensitivity to donor-like impurities like iron and their resistance to light-induced degradation brings more recent attention to the studies on the p+ emitter and its metal contact. In this work, we investigate the effect of the Boron doping profile on the quality of p+ emitter and their contacts with screen-printed Ag/Al metal fingers. The emitters within the scope of this study are created with BBr3 diffusion in an atmospheric diffusion furnace on n-type Si wafers and also applied to n-PERT Si cells to analyze their effects on device performance. Our results highlight the significance of the doping profile for solar cell performance, as it considerably affects the contact resistivity at the emitter-metal interface and the saturation current densities for emitter (J0, emitter) and Ag/Al metal contacts (J0, AgAl). Reducing the Boron concentration within the emitter leads to a decrease in carrier recombination in the non-contacted region of the emitter, which in turn decreases J0, emitter. However, this reduction increases the recombination in the contacted areas of the emitter, consequently elevating the J0, AgAl, and increasing the contact resistance values. Besides, the power loss analysis and simulation results based on experimental values obtained for our best solar cells group show how much J0, emitter and J0, AgAl values contribute to and would improve solar cell efficiency. The manuscript presents a case study of experimental emitter doping profile optimization applicable to similar n-type PERT or TOPCon cells with varying design parameters.