Link for the paper is given below.

Conference Paper Numerical Study of Based Perovskite Solar Cells by SCAPS-1D

Hi Dinesh Beniwal ,

The maximum value of short-circuit current density a certain absorber material can give depends on its band gap. Theoretically, if all loss processes by recombination could be ignored, i.e. your cell has a quantum efficiency of 100% for all photon energies above the absorber band gap (and 0% below), you can calculate the jsc value simply by counting photons in the AM1.5G spectrum above that energy. Thereby, lowering the band gap will give you an ever higher jsc. Counting all photons in the solar spectrum, i.e. band gap = 0eV, gives jsc = 68.9 mA/cm² according to a short calculation I just did.

On the other hand, lowering the band gap also decreases the output voltage of the cell. Since efficiency is a product of both, it will peak for some band gap value in between -- and it happens to do so at 1.1eV, for which the jsc you cite (~43mA/cm²) holds.

Now, looking at that paper, this is just a simulation. They specifically say that they haven't made such a cell. Based on what I said above, I would also doubt that someone can -- their absorber band gap is 1.55eV, which should give lower jsc than ~43mA/cm². My guess is that they have not used the AM1.5G spectrum for simulation (they don't specify in the paper, SCAPS has numerous possibilities to simulate illumination with various spectra).

Why not go ahead and ask them, if they're here on RG? :)

Regards,

Robert

Hello Dinesh,

you ask an interesting question.The fundamental limit for photo diodes is defined by the Shockley-Queisser limit ( see Wikipedia ). The efficiency which can be reached depends on the gap energy Eg of the semiconductor. The maximum theoretical efficiency at Eg = 1.5 eV is nearly 46%. For a reference power of P =100 mW/cm² (AM1.5 spectrum) follows a maximum current density of jmax = e*Pmax/Eg = 100 mW/cm²/1,5 V = 30.7 mA/cm². (e- elementary charge). You see, you have a relation between gap, efficiency and current density. Now I write the following table using the Queisser limit (ultimative limit) for different semiconductor:

Eg/eV Pmax/% j / mA/cm²

1,5 46 30.7

0.9 (Si) 40 44

0,5 30 60

From the table follows, the values, you know, are the characteristic values for silicon. If the gap is reduced (probably for PCE in the paper, you cited), you have a lower quantum efficiency but a higher current density.

I hope, I could help.

With Regard

Rüdiger Mitdank

Let me add a supplement to my last remark:

The gap energy of 0.9 eV is not valid for Si, but for an alloy of Ge and Si. I add the numbers for 1.1 eV:

Eg = 1.1 eV: Pmax = 45mW (45%); J = 41mA/cm²

Furthermore, I try to rewrite the upper table in a more readable form (The space sign doesn't work in this editor)

Eg/eV________Pmax/mW________j/(mA/cm²)

1,5____________46_______________30.7

1.1____________45_______________41

0.9____________40_______________44

0.5____________30_______________60

Two gaps must be attenuated

Direct and indirect

Kind regrad

Qusay Kh. Al_Dulamey

Dear all,

Thanks for your answers. Clearly they have not mentioned illumination intensity (concentrated or non-concentrated) and spectrum condition (AM-X) used. But now I have a better understanding of the theoretical limit for the calculation of Jsc value.

I will follow up with you guys if I receive any clarification from ther their side :).

Thanks and kind regard,

Dinesh

Dear Dinesh,

the values, I gave are valid for a nonconcentrated sun-spectrum (100 mW/cm² - AM1.5). For higher illumination intensities, the current is higher.

The situation changes too for other spectral conditions (monochromatic illumination or other. The Shockley-Queisser limit is calculated for a solar spectrum.

Furthermore, the solar cell must be a single junction. Tandem solar cells give a higher efficiency and higher current density.

The values you cited are all realized with single junction solar cells and solar illumination (spectrum and intensity).

With Regards

R. Mitdank