I have prepared the semiconducting material for solar cell applications, and I need to calculate the recombination rate and the lifetime of solar cells devices.
Dear Sadhanandam,
Your question is a basic one concerning the variation of the recombination rate U from the bulk to the electrodes.In principle the recombination rate depends on the excess minority carrier density, say delta n, and the minority carrier lifetime ,Tau and specifically it is expressed by U = delta n/ Tau. The lifetime Tau is a material parameter and can vary from point to point in the material depending on density of the recombination centers in that point. Deep laying impurities and crystallographic defects may act as effective recombination centers. A homogeneous semiconductor material has constant density of recombination centers in the bulk and therefore constant minority carrier lifetime. HOWEVER, at the surface and at interfaces with metallic electrodes, there are normally high density of recombination centers because the interruption of the malarial and the presence many unsaturated dangling bonds.e
You can measure the minority carrier lifetime of a semiconductor by the photconductive decay method.
Concerning the excess minority carrier profile, it is controlled by the injection, diffusion, and recombination of the minority carriers. It is determined by solving the semiconductor equations in the regions of interest in the device with the proper boundary conditions. It is always so that the minority carrier excess will be largest at the injection boundary and zero or very small at the metallic contact. The zero at the metallic contact is the consequence of the assumed infinite recombination rate at the metallic electrode as explained previously. When the recombination rate is infinite, the excess must tend to zero.
The surface recombination rate can be controlled by passivating the surface of the semiconductor. Also, the minority carrier in the bulk can be controlled by adding or removing deep lying impurities and or crystallographic defects.
Knowing delta n and Tau one can determine the recombination rate profile.
For more detail refer to the link
https://www.researchgate.net/publication/236003006_Electronic_Devices?ev=prf_pub and the link:
https://www.researchgate.net/publication/236002879_A_course_on_photo-voltaic_array_systems?ev=prf_pub
wish you success.
Book Electronic Devices
Book A course on photo-voltaic array systems
Mr.Abdelhalim Zekry. U = delta n/ Tau is the formula to calculate the Bandgap? i need good reference from you to calculate the Bandgap of the materials. thank you
Normally semiconductor materials characteristics are experimentally determined.
- The lifetime of minority carriers is measured by the photo conductive decay experiment.
- The band gap energy is determined by the absorption edge of photo spectrum.
- The mobility is measured by the time of flight mobile charge carriers across certain distance.
- The carrier concentration is measured by the Hall effect.
-The conductivity is measured by measuring the conductance of a rectangular bar material with known dimensions.
There are other measuring methods and other parameters.
You can consult the standard references in such topics.
I would like to advise you to take care of the principles of semiconductor materials and devices.
Lastly the formula above is not used to calculate the band gap.
Wish you success.
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