this is regarding simulating solar cells using comsol semiconducting module. I have a slab of semiconductor sandwiched between two schotkky contacts. I define the generation profile as an interpolation function, and solve the drift diffusion eqn to calculate the extracted current at end terminals. when the bulk recombination term is set to zero, I expected the short circuit current density to be equal to the total number of absorbed photons ( or the generation profile), but the calculated Jsc is less than that, indicating some sort of recombination taking place. I'm trying to find where this is happening. Is it possible this loss occur due to recombination at the end contacts? is there a recombination term associated with schotkky contacts?
Thank you.
Dear Warantha,
Do you have steady state conditions or transient conditions? if you have steady state conditions and you have no recombination in the whole device, then, the photogenerated electron hole pairs will be separated and collected at the metallic electrodes. The metal semiconductor contacts have interfaces that contains defects and that can act as recombination centers and traps. I do not now how you model these metal semiconductor interfaces and what is the default model in your device simulator. If you observe the electron and hole profile you may explore whether a recombination process at the interfaces exists or not. If there is only one dominant type of charges then the recombination will be very less probable.
You have also to review your calculations to become sure of the effect.
wish you success
This is a polymer solar cell. But at this step, I'm using the drift diffusion formula with Recombination rate set to zero to verify charge conservation. So I guess it does not matter much about the specific type of solar cell.
Dear Warantha,
Do you have steady state conditions or transient conditions? if you have steady state conditions and you have no recombination in the whole device, then, the photogenerated electron hole pairs will be separated and collected at the metallic electrodes. The metal semiconductor contacts have interfaces that contains defects and that can act as recombination centers and traps. I do not now how you model these metal semiconductor interfaces and what is the default model in your device simulator. If you observe the electron and hole profile you may explore whether a recombination process at the interfaces exists or not. If there is only one dominant type of charges then the recombination will be very less probable.
You have also to review your calculations to become sure of the effect.
wish you success
Dear Prof.Zekry,
Thank you for your answer. I'm using steady state. I was trying to make the recombination zero to verify that all the generated charges are collected at the end electrodes. The answer does not match up with the generation term, and I'm trying to locate if there is an unintentional recombination term still present in my simulations, or this is due to some computational error. For the contacts there aren't any specified recombinations. I have noticed the extracted current depend on the temperature input, and extracted current is higher at lower temperatures. So I believe there must be a thermal process included in the basic semiconductor model of COMSOL. But still unable to isolate the process.
Dear Warantaha,
Is there any build up of the electrons and holes with time. If here is no computational error and the collected current is smaller than generation rate time the volume of he specimen subjected to the incident photon flux then there must be growth of the charge carriers inside the specimen.
The charge balance is such that the current I= q A L G where A the cross sectional area, L the length in the direction of current flow and G the generation rate which i assumed to be constant or uniform in the whole volume. So, the check is straight forward.
I would propose to change the length of the specimen to see it effects and see if any storage effect or not.
wish you success.
For polymer solar cell it will not be a matter I guess.
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