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 design of silicon solar cells.
A world record conversion efficiency of 26.81% has been achieved recently by LONGi team on a solar cell with industry-grade silicon wafer (274 cm 2, M6 size). An unparalleled high fill factor ( FF) of up to 86.59% has also been certified in a separated device.
The "fill factor", more commonly known by its abbreviation "FF", is a parameter which, in conjunction with V oc and I sc, determines the maximum power from a solar cell. The FF is defined as the ratio of the maximum power from the solar cell to the product of V oc and I sc so that:
Therefore, the FF is most commonly determined from measurement of the IV curve and is defined as the maximum power divided by the product of I sc *V oc, i.e.: The equation for a solar cell is: I = I L − I 0 [exp (V n V t) − 1]
The maximum theoretical FF from a solar cell can be determined by differentiating the power from a solar cell with respect to voltage and finding where this is equal to zero. Hence: giving: V M P = V O C − n k T q l n (q V M P n k T + 1) It is an implicit equation, but it converges rapidly with iteration.
The data points of different high-performance silicon solar cell are located between the two blue dashed lines marked by RS = 0.2 Ω·cm 2 and RS = 0.4 Ω·cm 2, indicating they obeys the trend of “intrinsic recombination + surface recombination” curve but with RS of 0.2–0.4 Ω·cm 2. Realization of ultra-high FF in c-Si solar cell.