Comparative Analyses Between Two Techniques To Understand Metal-Induced Recombination Losses In Industrial N-Type Bifacial PERT Solar Cells

Abstract

Due to the high cell efficiency, low Light-Induced Degradation (LID) and high bifaciality, n-type bifacial passivated emitter and rear totally diffused (PERT) solar cells are being widely researched and currently being implemented in mass production. With the improvement of dopant profiles and passivation quality, J0,emitter and J0,bsf under passivation area could reduce to lower values. However, the Voc of cell is still not high enough which may be caused by the high recombination loss under metal area. In this paper, two different methods which are suitable for low cell efficiency diagnoses are investigated and compared to evaluate the J0,metal on both boron and phosphorus doping side of solar cells. For the first method, high resistivity n-type mono wafers are prepared with double front side or rear side structure of solar cell. Four different types of metallization ratio areas are designed on the one wafer of single side. By testing the J0,total of these four area, we can fit a line of J0,total with different contact fraction, so the J0,metal can be calculated by the expression of J0,total, J0,passivation and contact fraction. For the second method, Suns-Voc and Suns-PL are used for calculation. Four types of cell structures with metal, without metal, only with front metal and only with rear metal are fabricated to measure the probed Voc and PL derived Voc either use (i) different carrier injection levels or (ii) different light illuminations. A line can be fitted under different Suns, and by contrasting the line of cell structure and other structures, J0,metal of front metal and rear metal can be calculated by the bias of these lines. By comparing this two methods, we get the boron side Ag/Al paste J0,metal and the phosphorus side Ag paste J0,metal are around 2801 fA/cm2 and 964.9 fA/cm2, respectively. By comparing this two methods, the value of second method is lower than the first method and more appropriate for IV simulation using Quokka.