To give a few starting points to this complex field:

The EDNA calculation tool from Keith R. McIntosh and Pietro P. Altermatt is perfectly suited to investigate this topic. It calculates saturation and collection currents for the dopant profile of interest. You find the tool here:

http://www.pvlighthouse.com.au/simulation/Hosted/EDNA/EDNA.aspx

EDNA Reference:

K.R. McIntosh and P.P. Altermatt, “A freeware 1D emitter model for silicon solar cells,” Proc. 35th Photovoltiac Specialists Conference, Honolulu, pp. 2188–2193, 2010.

Further I recommend the following papers:

A. Cuevas et al. The effect of emitter recombination on the effective lifetime of silicon wafers (http://dx.doi.org/10.1016/S0927-0248(98)00179-2)

Cuevas, A. et al. Surface recombination velocity of highly doped n-type silicon, J. Appl. Phys., 80 (6), 3370-5, (1996).

King, R.R., R.A. Sinton, and R.M. Swanson, Studies of diffused phosphorus emitters: saturation current, surface recombination velocity, and quantum efficiency, IEEE Trans. Electron Devices, 37 (2), 365-71, (1990).

P.P. Altermatt, J.O. Schumacher, A. Cuevas

Numerical modeling of highly doped si:P emitters based on fermi-dirac statistics and self-consistent material parameters; Journal of Applied Physics, 92 (6) (2002), pp. 3187–3197

We also did some work on this topic, you might want to look into this paper from A. Kimmerle: http://dx.doi.org/10.1016/j.egypro.2011.06.136

Best, Daniel

Thank you Daniel for listing some useful literature covering the effect of the emitter layer on the solar cell efficiency. But i intend to present the results of the research work on this topic and make them available to the researcher of the researchgate.

Zekry

Dear colleagues, It seems that i see that certain subject may be of some general importance and so i put a question on it to establish a discussion around it and make it more clear.In spite of the importance of this question:How does the n+ emitter layer affect the performance of the n+p Si solar cells? i obtained only one answer from Daniel Biro. Such situation happened with me in previous questions. The question is if i answered this question would it be useful to researchgate researchers?

I will answer this question in several comments.

I will start with junction depth. As the junction depth increases, the reverse saturation current of the cell decreases and the opencircuit voltage increases. On the other side, the dead region part of the n+emitter near the cell surface increases. The dead region is a region with very small minority carrier lifetime leading to killing the photogenerated eh pairs. Therefore the cell response to the photons with short wave lengths becomes weaker and the the photocurrent Iph will be smaller by increasing the the junction depth. Therefore, there is an optimum junction depth which maximizes the solar cell efficiency with the solar cell. This thickness is about 0.2 um.

Concerning the effect of the doping concentration, as the doping concentration increases, the reverse saturation current decreases and the opencircuit voltage of the cell increases. Increasing the doping concentration beyond certain optimum value leads to band gap narrowing which results in the increase of the reverse saturation current and the reduction of the open circuit voltage. Bandgap narrowing is a consequence of heavy doping effects. Therefore, there is an optimum doping concentration of the n+ emitter.Quantitative analysis and measurements showed that the optimum doping concentration is about 10^19/ cm^3.

In the next comment i will outline the effect of the minority carrier lifetime and surface recombination.

As the minority carrier lifetime in the emitter decreases the reverse saturation current of the solar cell increases leading to a reduction in the opencircuit voltage and the conversion efficiency. So, the minority carrier lifetime is made sufficiently high such that the the minority carrier diffusion length is greater than the junction depth.

As the surface recombination increases the reverse saturation current is raised and consequently the opencircuit voltage decreases leading to reduction in the conversion efficiency. Moreover, the high recombination at the surface leads to killing the photogenerated e-h pairs and consequently reducing the the photocurrent , which causes an additional decrease in the conversion efficiency.

In order to mitigate the effect of high surface recombination velocity, the surface is passivated using silicondioxide. On this way the silicon solar cells will be more sensetive to ultraviolet radiation and the cell is termed UV cells.

UV cells are SI solar cells with optimum emitter profile and surface passivation.

Thank you

Thnk u prof. Can u please tell me why there is a n++ layer under top surface contact of a si solar cell?

Dear Jayakumar,

welcome!

Hope you are well!

The heavy doping concentration has the followings benefits:

- It reduces the reverse saturation current of the solar cell n-p junction and thereby leads to an increase in the opencircuit voltage Voc. This improves the photo conversion efficiency.

- It decreases the resistance of this layer and thereby contribute to the reduction of the series resistance. It leads then to an increase in the fill factor and the PCE.

- The metal silicon contact will be ohmic and its resistance will be smaller leading to higher PCE.

Best wishes

Thank you so much for your immediate response.

Prof, can u tell me the importance of majority vs minority charge carriers in a pn junction solar cell?