The dual-junction solar cell composed of two sub-cells would achieve a better conversion efficiencies, but how does the current flow in the tunnel junction P++/n++ withou current loss?
Dear Idris,
Ideally one has to the contact between cells behaves as an oh-mic with much smaller resistance than the other layer resistances of the device.
The ohmic contact that has a linear I-V curve can be accomplished by very high recombining interface where the interface can sink both types of the charges.
The tunnel junction can also behave ohmic around the the origin point where it conducts equally in the forward and reverse direction thanking to the tunnling of the electrons from both sides of the interface based on its energy band diagram.
Best wishes
Dear Dr. Idris
In two junction solar cells, we can connect them in 4-terminal [ the two cells are electrically isolated], or 2-terminal [the two cells are connected by the tunnel junction]. Theses tunnel junction has a lot of criteria to achieve its function properly like: transparent at long wavelengths where the bottom junction absorbs. The material and shape selection for this layer based on reducing their current and optical losses as much as possible, but in general, there will be some losses for them.
Kind regards.
M.Elshorbagy
Dear Idris,
many researchers covered the dual junction solar cells and recent research about multi junctions solar cells. please read papers below:
1- "Modelling of Dual-Junction Solar Cells including Tunnel Junction" . Hindawi Publishing Corporation Advances in Condensed Matter Physics Volume 2013, Article ID 546362, 5 pages http://dx.doi.org/10.1155/2013/546362 .
2- "Modeling of Tunnel Junction of Multi-junction Solar Cell" . Recent Researches in Energy, Environment and Sustainable Development .
3- "Tunnel Junctions for III-V Multijunction Solar Cells Review". Crystals 2018, 8, 445; doi:10.3390/cryst8120445 .
In a true tunnel junction the carriers tunnel from the valence band of p++ to the conduction band of n++, through the band gap. The junction has to be extremely thin for this to work.
In practice, all a tunnel junction needs to do in a tandem cell is provide an optically transparent Ohmic contact between the two cells. Often these junctions aren't strictly tunnel junctions but they do the job. You can google for example tunnel recombination junction (TRJ), or look at what is used in a-Si/µc-Si tandems and perovskite/silicon tandems.
Dear Idris,
Ideally one has to the contact between cells behaves as an oh-mic with much smaller resistance than the other layer resistances of the device.
The ohmic contact that has a linear I-V curve can be accomplished by very high recombining interface where the interface can sink both types of the charges.
The tunnel junction can also behave ohmic around the the origin point where it conducts equally in the forward and reverse direction thanking to the tunnling of the electrons from both sides of the interface based on its energy band diagram.
Best wishes
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