A world record conversion efficiency of 26.81% has been achieved recently by LONGi team on industry-grade silicon wafer (274 cm 2, M6 size). An unparalleled high fill factor ( FF) of up to 86.59% boosted the cell performance. The theoretical FF limit has been predicted to be 89.26%, while the practical FF is far below this limit for a prolonged interval due to the constraints of recombination ( i.e., SRH recombination) and series resistance. The ideality factor ( m) in the equivalent circuit of silicon solar cells is consistently ranging from 1 to 2 and rarely falls below 1, resulting in a relatively lower FF than 85%. Here, this work complements a systematic simulation study to demonstrate how to approach the FF limit in silicon solar cell fabrication. Firstly, a diode component with an ideality factor equal to 2/3 corresponding to Auger recombination is incorporated in the equivalent circuit for LONGi’ ultra-high FF solar cell; Secondly, an advanced equivalent circuit is put forward for comprehensive analysis of bulk recombination and surface recombination on the performance, in which specific ideality factors are directly correlated with various recombination mechanisms exhibiting explicit reverse saturation current density ( J 0); Finally, we evaluate precisely the route for approaching theoretical FF in practical solar cell fabrication based on electrical design parameters using the developed model.
With the improvement of surface passivation, bulk recombination is becoming an indispensable and decisive factor to assess the limiting efficiency ( η lim ) of crystalline silicon (c-Si) solar cells. In simultaneous consideration of surface and bulk recombination, a modified model of η lim evaluation is developed. Surface recombination is directly depicted with contact selectivity while bulk recombination is revised on the aspects of ideality factor and wafer thickness. The η lim of cutting-edge photovoltaic technologies, double-side tunneling-oxide passivating contact (TOPCon) and silicon heterojunction (SHJ) solar cells, are numerically simulated using the new model as 28.73% and 29.00%, respectively. Hybrid solar cells consisting of n-type TOPCon contact and p-type SHJ contact can approach an η lim as high as 29.18% at the optimal wafer thickness ( W opt ) of 103 μm . Our results are instructive in accurately assessing efficiency potential and accordingly optimizing design strategies of c-Si solar cells.