What are their functions and what would happen if they were not there? Any article or book will be apreciated.
Dear José María Cuevas Dávila ,
The transport layers are necessary for organic solar cells because the active donor acceptor blend can be considered an intrinsic layer with very low dark carrier concentration. So, the solar cell is constructed as PIN diode, where one side will be the HTL and the other will be the ETL. The hole transport layer must be p-type with high conductivity and the electron transport layer must be n-type with high conductivity. The energy levels of both the ETL and the HTL must be correctly aligned to those of the active layer. The HTL must have energy levels to attract holes from the active layer and repel electrons and the ETL must have levels to convey electrons away from the active material and repel holes.
If the perovskite material is intrinsic as in the case of the organic blend then to work properly as solar cells they need also ETL and HTL. to form a PIN structure.
Since the perovskites can be doped with impurities' to make them either p-type of n type, one can construct solar cells from them from homo pn junctions as in the case of silicon. One can also build solar cells based on pn heterojunctions where the solar cell is constructed from the perovskite as an absorbing layer and a wideband window layers.
I would like turn your attention to the papers:Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells
Article Investigating the performance of formamidinium tin-based per...
Best wishes
The ETLs in PSCs play important roles in collecting and transferring charge carriers after the injection of electrons from a perovskite active layer, more importantly, realizing effective charge separation and suppressing charge carrier recombination.
The presence etl and htl impacts the built in potential within the cell which enables proper separation of electron and holes generated under the illumination. Apart from carrier separation, it also enables transportation of electrons and holes via etl and htl respectively by avoiding Carrier recombination before being collected by the charge selective contacts.
Priyanka Roy , could you explain more about this built in potential?
Dear José María Cuevas Dávila ,
Hope you are well!
It is so that the HTL and the ETL build pin junction with the active perovskite layer.
The contact difference of potential across this junction is difference between the work function of the HTL and the that of the ETL . The contact difference of potential is such that the ETL is at higher potential than the HTL which build an internal electric field in the active region with the electric field directed from the ETL to the HTL.
An incident photon with proper energy will generate electron hole pairs in the active absorber layer, The built electric field separates them and moves the hole towards the ETL and the electrons towards the ETL where they will be collected.
I would like that you follow the paper: Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells
you will fine a complete analytical solution of the problem!
Best wsihes
Dear Jose Cuevas
Consider a perovskite solar cell without HTL and ETL. It there are no transport layers then there will be just metallic contacts and TCO's on either side. One of the disadvantage of that will be that there will be huge recombinations. Second there will be energy loss since pair dissociated will have to move from directly from perovskite conduction band towards the respective electrode. Third the device will also likely to suffer from the pinning effect of Fermi level. Also the device will show poor performance.
So in order to avoid all these problems along with few other, ETL and HTL are used. As mentioned above by the other fellows, both of these layers create a built in potential which help in the dissociation of the exciton along with the smooth transfer of charges with lower resistance and without the loss of useful energy by providing suitable energy levels. Also these layers will reduce or eliminate the chances of charge recombinations. Also since some of the materials have excellent stability in the ambient atmosphere so they will also add up to the stability, longer lifetime and enhance performance of the Perovskite device fabricated.
- Badges
- Science topic