Fig. 4: The champion module results and related cell-to-module loss analysis.
a The certified result from Fraunhofer ISE. The module has 75 units of FBC cells in total with smart-wire zero-busbar interconnections as the stringing technology. b Cell-to-module loss analysis, especially for series resistance and FF. The top three loss terms are from majority carrier lateral spreading (TCO resistivity and carrier drift‒diffusion), front-side TCO‒Ag contact RC (~0.8 mΩ cm2) and front-finger line resistance. The front-finger line resistance loss at the cell side is estimated on the basis of an 18 BB assumption at the cell side, but a 28 BB configuration at the module side. The series resistance loss from the front-side ribbon is based on a round cross-section with a 220-µm-diameter inner core. There is other Rs loss from the backside ribbon, end connection and short cabling. c The specially defined CTM loss from the champion cell to the champion module. The FBC data are based on this work, but the BC data come from Martin A. Green’s “Table” (v 65). d Comparison of the certified cell results with the parametric modelling results: pseudo J–V with the assumption of τSRH = 15 ms, J01 = 1 fA/cm2, and J02 = 0 nA/cm2; a simulated J-V with an RS of 0.2 Ω cm2 added to the pseudo J–V curve; and a J–V curve with an additional J02 = 0.5 nA/cm2 recombination source. All the modelling is based on a wafer thickness of 130 µm and resistivity of 1.5 Ω cm. e pFF (or FF0) versus VOC curve. In the regime dominated by surface recombination J01 (Zone 1), the ideality factor n of the I‒V curve approaches 1, and VOC is typically less than 740 mV. In Zone 3, when both surface recombination terms diminish and τSRH approaches infinity, pFF quickly climbs up in this Auger-recombination-dominated regime. In this situation, the ideality factor is close to 2/3. In the interim, around the vicinity of VOC = 750 mV, the upper limit of pFF also ramps up quickly, with fast reductions in both J01 and J02.
