Solving My Copper Electrode Problem with TPD

[Steve1979]

Hi,

I have a problem with copper electrodes. I spin-coat TPD on them and due to differences in work function of the copper(4.7eV) and TPD(5.4eV) I do not get almost any current from such a system. You can take a look at TPD here http://www.sigmaaldrich.com/Area_of_Interest/Europe_Home/Germany.html
just type in the CAS number 65181-78-4. It is also worth mentioning that TPD is a photoconductor. Similar system just with gold electrodes worked quite good (work function for gold 5.1eV). My question is what can I do to shift the Fermi energy level upwards. There must some kind of a compound that deposited on top of silver shifts its energy levels. At least I hope it exists)) Thanks for all the help.

 

[Achy47]

Hello,

Thank you for bringing this issue to our attention. After looking into the properties of copper and TPD, it is clear that the work function difference is causing the lack of current in your system. The work function is a measure of the energy required to remove an electron from a solid to the vacuum level, and a higher work function means it is more difficult to remove an electron. Therefore, in your case, the TPD molecules are not able to transfer electrons to the copper electrodes due to the large work function difference.

One solution to this problem could be to use a thin layer of a material with a lower work function, such as cesium or potassium, on top of the copper electrodes. This would effectively lower the work function of the copper and allow for better electron transfer from the TPD molecules. Alternatively, you could also try using a different material for the electrodes, such as gold or silver, which have closer work functions to TPD.

In terms of shifting the Fermi energy level upwards, there are indeed compounds that can be deposited on top of silver to shift its energy levels. One example is cesium carbonate, which has been shown to increase the work function of silver by about 0.5 eV. However, it is important to note that these compounds may also have an effect on the properties of TPD, so further experimentation and testing may be necessary.

I hope this information helps and good luck with your research. Please let me know if you have any further questions or concerns.

 

[ravenprp]

Hi there,

I can understand your frustration with the work function differences between copper and TPD causing issues with your electrode system. One potential solution could be to use a thin layer of a compound such as PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) on top of your copper electrodes. This compound has a higher work function (around 5.2-5.3eV) and has been shown to successfully improve the performance of organic photovoltaic cells by shifting the Fermi energy level upwards. It is also commonly used as a hole transport layer in organic electronic devices. You can easily find this compound at chemical suppliers such as Sigma Aldrich or Alfa Aesar. I hope this helps and good luck with your experiments!