Four terminal solar cells need at least three transparent electrical contacts and have shown better efficiency than that of two terminal solar cells. This is probably due to more charge carrier generation/separation/recombination. Now question arises what is the detailed working mechanism of four terminal (4-T devices) solar devices/PSCs and in which way they differ from two terminal solar devices (2-T devices)?
Hope you are well all!
In the two terminal tandem cells the top cell and bottom cell must be designed to have the same short circuit current. This imposes a condition on the spectrum sharing that must not necessarily globally optimum.
In addition there must be a tunneling contact between the two tandem cells.
The basic idea behind the four terminal solar cells is overcome the constraint of the same current and producing the stunning contact by stacking to cells one on the top of the other each cell has its optimum operating conditions. Then they can connected in parallel instead of the series connection.
Even if the one made the currents eqaul then it remains that one can construct each cell for the highest harvesting.
I think there will be a problem for wiring. Two terminal is much better amenable for building modules.
The colleagues brought good papers in this topic.
Best wishes
In both two and four-terminal solar cells each sub-cell absorbs a specific part of the solar spectrum, short wavelengths absorbed on the top cell and long wavelengths absorbed in the bottom cell. The bandgap of the two cells has to be selected to make both cells efficiently work in their corresponding band. Then the main difference between both designs is that four-terminal devices are electrically isolated and mechanically stacked on top of each other having a dielectric spacer in-between usually glass. In two-terminal devices, both cells are electrically connected through the tunnel junction [ which needs to be transparent at least for long wavelengths]. Any way each design has some advantages and disadvantages some of them are summarized in this article.
Article Efficient Light Management in a Monolithic Tandem Perovskite...
Dear Hasan Abbas,
kindly read the paper below it describes the different types of solar devices.
1- Todorov, T., Gunawan, O., & Guha, S. (2016). A road towards 25% efficiency and beyond: perovskite tandem solar cells. Molecular Systems Design & Engineering, 1(4), 370–376. doi:10.1039/c6me00041j .
Fig. 1 Types of tandem solar cell device based on the number of TCEs and terminal connections: (a) type A: single TCE, two-terminal monolithic; and type B with multiple TCEs: (b) two-terminal mechanically stacked, (d) 4-terminal mechanically stacked, (c) 3-terminal monolithic stack and (e) 4-terminal spectrum-split.
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Fig. 2 Performance comparison of various tandem configurations (2, 3 and 4 terminals) based on idealized SQ-limit calculation vs. bandgap of the top cell. The bottom cell is Si (1.1 eV) which is filtered by the top cell: (a) J-V curves under AM1.5G 1 sun light for the top cell with E g2 = 2.0 eV. (b) Efficiencies of the constituent cells and the tandem cells.
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Hope you are well all!
In the two terminal tandem cells the top cell and bottom cell must be designed to have the same short circuit current. This imposes a condition on the spectrum sharing that must not necessarily globally optimum.
In addition there must be a tunneling contact between the two tandem cells.
The basic idea behind the four terminal solar cells is overcome the constraint of the same current and producing the stunning contact by stacking to cells one on the top of the other each cell has its optimum operating conditions. Then they can connected in parallel instead of the series connection.
Even if the one made the currents eqaul then it remains that one can construct each cell for the highest harvesting.
I think there will be a problem for wiring. Two terminal is much better amenable for building modules.
The colleagues brought good papers in this topic.
Best wishes
Abdelhalim abdelnaby Zekry (Sir), Abd El-Aziz M. Mansour (Sir), and M.H. Elshorbagy (Sir), thank you so much.
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