I intend to make flexible OSC using CNT electrodes, so it is possible to use CNT as both the contacts? ( Given that we have electron and hole transfer layer between active layer and contacts)
Dear Prithu
Do you refer OSC as an organic solar cell? If so the answer to your question is NO!
Firstly when you design an OPV or OSC to consider electrode layers either transparent electrode or reflective electrode, you need to consider the energy alignment to the layer contact with. In another word, how to inject electrons or holes via electrodes. The answer to this, it is very difficult to use the same electrode material to inject holes and electrons at the same time in one cell.
Secondly to use CNT thin films as electrodes, the conductivity has to be high enough comparing with the conventional materials used as electrodes. The answer to it is most of CNTs that only one third of CNTs are conductors and two third of CNTs are semiconductors. Again it is difficult. There are some work published using SWCNTs as a transparent electrode. One of our work was published in
https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.200902369
What is more, there are other requirements to an electrode material used for OPVs on flexible substrates too.
There is no doubt that CNT materials have excellent mechanical and thermal properties. To apply such materials for flexible OPVs, they are limited and also costly.
I hope I answer your question.
Best wishes
Xuhua
Xuhua Wang thanks for your reply, but I am already using electron and hole transport layer along with the electrodes.
About quality of CNTs , I have 90% transparent CNT with 50 ohm/cm^2 Sheet resistance and a thick, opaque SWCNT film with 10-20 ohm/cm^2 sheet resistance.
what concern me is the energy band.
Please add your comment
thanks
Prithu Roy
You did a great job to have very good conductivity. You could use CNT transparent electrode as the hole injection electrode. You could try to use an interlayer to assist the electron injection such as Cs2CO3. You may need to dope your opaque CNT electrode to tune the energy level close to the work function of aluminium which a normal cell usually does. Hope it helps.
Dear Xuhua Wang , can i use CNT as hole-transporting material and carbon (graphite 5 micron mixed with carbon black N330) as counter electrode? (transparency is not needed)
Dear Soo Yew Hang
You could use semiconducting CNT as a hole injection and transport layer as long as the energy level aligning with the layer i.e. an active layer of organic semiconductor. Normally It does. However, It may be difficult to use cabon black as an electron injection electrode if you use it alone due to the energy misalignment with most of electron transport materials. Again doping electron pulling materials into carbon black may work well to tune the energy level.
Hope it helps.
I forget to mention that the tube diamrter of average CNTs is crucial to use either conductors or semiconductors. It is very often to have rough films from CNTs, which could lead to failure of the devices due to the shorts generated through the devices. Therefore, some post special treatments after film formed may be needed to make smooth films such as heat and pressure treatments. Hope it helps.
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