Analysis of the Emitter Saturation Current Density of Industrial Type Silver Screen-Printed Front Contacts

Abstract

Selective emitters for industrial-type silicon solar cells have gained increasing attention in the past years. However, the assessment of the improvement potential of a selective emitter so far mainly relies on the obtained conversion efficiency of the resulting solar cells. In this paper we employ using the dynILM method to measure the emitter saturation current densities on SiNx passivated (J0e,pass) as well as Ag screen-printed (J0e,met) phosphorus emitters on test wafers which are similar to industrial-type silicon solar cells. The J0e,met of the Ag screenprinted emitter increases from 210 fA/cm2 up to 570 fA/cm2 with increasing sheet resistance. In contrast, the J0e,pass decreases from 147 fA/cm2 to 95 fA/cm2 with increasing sheet resistance. Compared to previous work on laboratory type cell structures, our results show lower J0e,met values and higher J0e,pass values which might be explained by the different emitter profiles. The measured J0e,pass and J0e,met values allow to calculate the total emitter saturation current density J0e,total. For a homogeneously doped 60 Ω/sq emitter we predict a J0e,total of 140 fA/cm2. A selective Emitter with 30 Ω/sq below the metal contacts and 100 Ω/sq below the SiNx passivation results in a J0e,total of 106 fA/cm2. The reduction in J0e,total corresponds to an approx 3 to 5 mV higher Voc compared to the homogeneously doped emitter.