Surface Recombination Velocity

I am trying to add surface recombination velocity (interface effect) in my simulation and I simulated the following file with different surface recombination velocities. However, SRV has no effect when Ei=0(even in 1e7) , if I increased Ei (both in positive and negative values) then eta increases as well as short circuit current and open circuit voltage. As I know surface recombination velocity decreases the solar cell efficiency due to surface recombination, will you please point out my mistake in simulation? and please explain what Ei signifies physically ?
Happy valentines day and Thank you :slight_smile:

Hi @1105058.mmah, you can find detailed information about the surface recombination model in this KB page: Material interface. By default the trap level is assumed to be at the middle of the bandgap (Ei). The “Ei offset” value can be used to move the energy of the trap level closer to the valence or conduction band.

Regarding your value of surface recombination velocity not affecting the current (or rather affecting it in an unexpected way), I will take a look at your file and get back to you.

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Hi @1105058.mmah, Sorry for the wait again. The reason you do not see any effect of the surface recombination velocity of the photo-current is because in the case of metals (electrical contacts), surface recombination velocity only gets applied to minority carriers. This is mentioned in this KB page (Material interface) as well [under the “Semiconductor-Conductor” sub-section]. Since the photo-current is primarily due to majority carriers, the value of the surface recombination velocity do not affect it.

One thing to remember is that for metal-semicondcutor interface, an electron or hole approaching the interface due to surface recombination velocity eventually gets collected by the metal contact and contributes to the contact current. However, if both an electron and a hole gets collected then the corresponding current has different polarity and they cancel each other (and so you get a smaller current).

Now, since for a metal-semicondctor interface only the minority carrier get affected by the surface recombination velocty and a small value of the velocity means less minority carrier get collected at that contact, the total current at that contact will increase (since total_current = majority_carrier_current - minority_carrier_current). So, when you see a rise in the photo-current while playing with the surface recombination velocity or the trap energy, it means that you have reduced the number of minority carrier getting collected by the contact and thus increased the total current at that contact.

I hope this helped. If you still have questions do not hesitate to post them.

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Hi @aalam sir. Thanks for your long awaited reply :slight_smile:

  1. In solar cell,incident photon generates ehp pair in semiconductor, the minority carrier in between the depletion region and diffusion length gets collected on each side becomes the majority carrier on their respective side arises the photo current. If we disable the SRH carrier life time, then diffusion length of minority carrier becomes infinity and minority carrier generated on each side must be collected according to theory. As surface recombination velocity applies to minority carrier (which is in the case of metal semiconductor interface), the concentration of minority carrier at surface decreases and so the collection efficiency. Thus bulk photo current must be decrease.
  2. As bulk photo current = contact photo current, then contact current must be decreased. This phenomenon can be understood by your given equation.
    contact current=majority_carrier_current - minority_carrier_current, as minority carrier gets collected by the contact, minority_carrier_current at the contact increases, and the contact current decreases(as surface recombination velocity only affects the minority carrier, majority carrier concentration remains almost constant). The overall current then decreases with surface recombination velocity increases which is described in your example file(planar silicon solar cell).
    This is the two points that I understood from my logic. Please correct me if I am wrong.

Now according to your explanation…
in insulator/semiconductor interface (SiO2/nAl-ZnO in my simulation file) surface recombination velocity also applies to majority carrier. but it has also no effect.

One request is that,can you please tell me the way to model surface effects like conventional solar cell, (where current decreases with the increment of surface recombination velocity). I am actually looking for it for a long time (before posting that issue). I am hoping that you will solve my problem very soon.

Thanks :slight_smile:

Hi @1105058.mmah, You are right in your points 1 and 2. As you increase the surface recombination velocity in a metal contact, the collection of minority carrier goes up (no effect on majority carrier current). This means the minority carrier current goes up which reduces the overall contact current (photo-current).

For an insulator-semiconductor interface the surface recombination velocity applies to both majority and monitory carriers. Since the electron-hole pairs disappear from the system, the photo current will go down. However, note that the effect of surface recombination on the insulator-semiconductor surface will become noticeable only when you have a large interface (e.g. when you have a grated top surface). This is demonstrated in this example: 2D silicon square grating. Please take a look at this example as this one shows results that you are probably asking for.

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